![Ultraviolet protection factor (UPF) is primarily a measure of UVB protection whereas critical wavelength (CW) is a measure of the degree of broad-spectrum protection. (A) UPF is a mathematical function designed to recapitulate sun protection factor (SPF) from a laboratory measurement of transmittance and is weighted toward the UVB portion of the spectrum. Left: Plots of the erythemal effectiveness function (Eλ) and the solar spectral irradiance (Sλ) over the UVR spectral range. Right: The product of Eλ and Sλ has a peak that lies predominantly (75%) within the UVB range (280–315 nm). Very little of the UPF function comes from wavelengths longer than 360 nm, where the UVR intensity is highest but the erythemal effectiveness is near zero [48]. (B) Visual representation of the CW as the wavelength below which 90% of the total absorbance (area under the curve) in the UVR region is contained. Left: Hypothetical sunscreen that primarily blocks UVB radiation has a critical wavelength below the 370 nm threshold required by the FDA to be labeled broad-spectrum. Right: Hypothetical sunscreen with improved UVA blocking performance meets the broad-spectrum criterion. A sunscreen could meet the CW criterion of 370 nm without comprehensively blocking UVA radiation.](https://www.researchgate.net/publication/358048960/figure/fig1/AS:11431281210550167@1702052767119/Ultraviolet-protection-factor-UPF-is-primarily-a-measure-of-UVB-protection-whereas_Q320.jpg)
![Transmittance of organic sunscreen filters (tested in this study) and inorganic sunscreen filters (ZnO and TiO2). Data were obtained from the BASF sunscreen simulator [59] where the maximum concentration allowable by the FDA [46] was used to generate each curve.](https://www.researchgate.net/publication/358048960/figure/fig4/AS:11431281210550171@1702052769003/Transmittance-of-organic-sunscreen-filters-tested-in-this-study-and-inorganic-sunscreen_Q320.jpg)
![Transmittance spectra of the four fabrics designed for UV protection tested in this study (orange and purple lines) compared to “normal” clothing items tested by Coyne, et al. (gray lines). The data from Coyne, et al. were digitized, converted to transmittance and represent the average of the 16 measurements as reported in the original study. White cotton and dark grey cotton were GAP, Inc. 100% cotton shirts. The denim was 69% cotton, 30% polyester, 1% spandex GAP jeans. Polyester refers to a 84% polyester, 16% spandex Coolibar rash guard [71].](https://www.researchgate.net/publication/358048960/figure/fig5/AS:11431281210550172@1702052769407/Transmittance-spectra-of-the-four-fabrics-designed-for-UV-protection-tested-in-this-study_Q320.jpg)
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Citation: Berry, E.G.; Bezecny, J.;
Acton, M.; Sulmonetti, T.P.;
Anderson, D.M.; Beckham, H.W.;
Durr, R.A.; Chiba, T.; Beem, J.; Brash,
D.E.; et al. Slip versus Slop: A
Head-to-Head Comparison of
UV-Protective Clothing to Sunscreen.
Cancers 2022,14, 542. https://
doi.org/10.3390/cancers14030542
Academic Editor: Chalid Assaf
Received: 27 November 2021
Accepted: 11 January 2022
Published: 21 January 2022
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cancers
Article
Slip versus Slop: A Head-to-Head Comparison of UV-Protective
Clothing to Sunscreen
Elizabeth G. Berry 1, * , Joshua Bezecny 2, Michael Acton 3, Taylor P. Sulmonetti 4, David M. Anderson 4,
Haskell W. Beckham 5, Rebecca A. Durr 5, Takahiro Chiba 5, Jennifer Beem 5, Douglas E. Brash 6,
Rajan Kulkarni 1,7, Pamela B. Cassidy 1and Sancy A. Leachman 1
1Department of Dermatology, Oregon Health & Science University, Portland, OR 97239, USA;
kulkarnr@ohsu.edu (R.K.); cassidyp@ohsu.edu (P.B.C.); leachmas@ohsu.edu (S.A.L.)
2College of Osteopathic Medicine of the Pacific, Western University of Health Sciences,
Lebanon, OR 97355, USA; joshua.bezecny@westernu.edu
3Exponent, Inc., Natick, MA 01760, USA; macton@exponent.com
4Exponent, Inc., Atlanta, GA 30326, USA; tsulmonetti@exponent.com (T.P.S.);
danderson@exponent.com (D.M.A.)
5Columbia Sportswear Company, Portland, OR 97229, USA; HBeckham@columbia.com (H.W.B.);
rdurr@mit.edu (R.A.D.); taka.chiba@columbia.com (T.C.); Jennifer.Beem@columbia.com (J.B.)
6Departments of Therapeutic Radiology and Dermatology, Yale University, New Haven, CT 06520, USA;
douglas.brash@yale.edu
7Portland Veterans Administration Medical Center, Portland, OR 97239, USA
*Correspondence: berryel@ohsu.edu; Tel.: +1-(503)-418-3376
Simple Summary:
Photoprotection reduces invasive melanoma incidence and mortality, but not
all sun protection modalities are created equal. Dermatologists have long debated the pros and
cons of photoprotective clothing and sunscreen, but few studies compare the effectiveness of these
two modalities head-to-head. This study uses both
in vitro
and
in vivo
techniques to compare
the ultraviolet radiation (UVR) protective capacity of four modern textiles and two commercially
available, broad-spectrum sunscreens.
Abstract:
Ultraviolet radiation (UVR) exposure is the most important modifiable risk factor for skin
cancer development. Although sunscreen and sun-protective clothing are essential tools to minimize
UVR exposure, few studies have compared the two modalities head-to-head. This study evaluates
the UV-protective capacity of four modern, sun-protective textiles and two broad-spectrum, organic
sunscreens (SPF 30 and 50). Sun Protection Factor (SPF), Ultraviolet Protection Factor (UPF), Critical
Wavelength (CW), and % UVA- and % UVB-blocking were measured for each fabric. UPF, CW, % UVA-
and % UVB-blocking were measured for each sunscreen at 2 mg/cm
2
(recommended areal density)
and 1 mg/cm
2
(simulating real-world consumer application). The four textiles provided superior
UVR protection when compared to the two sunscreens tested. All fabrics blocked erythemogenic
UVR better than the sunscreens, as measured by SPF,UPF, and % UVB-blocking. Each fabric was
superior to the sunscreens in blocking full-spectrum UVR, as measured by CW and % UVA-blocking.
Our data demonstrate the limitations of sunscreen and UV-protective clothing labeling and suggest
the combination of SPF or UPF with % UVA-blocking may provide more suitable measures for broad-
spectrum protection. While sunscreen remains an important photoprotective modality (especially
for sites where clothing is impractical), these data suggest that clothing should be considered the
cornerstone of UV protection.
Keywords:
photoprotective clothing; photoprotection; sun protection factor (SPF); ultraviolet
protection
factor (UPF); critical wavelength (CW); skin cancer; melanoma
Cancers 2022,14, 542. https://doi.org/10.3390/cancers14030542 https://www.mdpi.com/journal/cancers
Cancers 2022,14, 542 2 of 19
1. Introduction
1.1. UVB and UVA Cause Skin Cancer via Cyclobutane Pyrimidine Dimers (CPDs)
Exposure to ultraviolet radiation (UVR) remains the most important and most modi-
fiable risk factor for the development of skin cancer [
1
,
2
]. As skin cancer incidence rises
worldwide, minimization of exposure to UVR is critical for reducing the morbidity, mor-
tality, and cost associated with skin cancer [
3
]. To achieve this, the American Academy
of Dermatology recommends sun avoidance, application of broad-spectrum sunscreen
(SPF 30 or higher), and use of hats and protective clothing [
4
]. Since avoidance of UVR
is not always possible, sunscreen and sun-protective clothing are essential features of a
multi-pronged approach to skin cancer prevention. Recent data from Queensland, Australia
underscore the fact that photoprotection is effective. Aitken et al. showed a decline in inva-
sive melanoma incidence and mortality in individuals under age 40 years in Queensland [
5
].
The steepest decline was in those born after 1980, the decade in which photoprotection
education initiatives such as the “Slip” (on a shirt), “Slop” (on sunscreen), and “Slap” (on a
hat) campaign were implemented [5,6].
Both UVB (280–315 nm) and UVA (315–400 nm) radiation are carcinogenic. Of note,
UVC (100–280 nm) is the most damaging type of UVR but is completely attenuated by
ozone in the atmosphere before reaching the earth’s surface. The UV portion of solar
radiation that reaches the earth’s surface comprises 5% UVB and 95% UVA radiation. UVB
is a higher energy radiation but is less able to penetrate through the skin than the longer
wavelengths of UVA. UVB causes erythema of skin and has historically been implicated
as the main contributor to the development of skin cancer [
7
]. UVB is directly absorbed
by DNA bases resulting in the formation of cyclobutane pyrimidine dimers (CPDs) and
6-4 photoproducts that can result in mutations if not repaired [
7
]. UVA causes pigment
darkening or tanning of the skin and is associated with photoaging [
8
]. Recent work shows
that UVA has a much greater role than previously understood in skin cancer development
due to its ability to induce reactive oxygen and nitrogen species, and ultimately generate
CPDs hours after UVA exposure [9–12].
UV-induced CPDs are more mutagenic than 6-4 photoproducts, likely due to their
slower repair [
13
]. The most common UV-induced mutation in human skin cancer is the
C>T transition. This mutation can be caused by the rapid deamination of cytosine (C)
or 5-methylcytosine in CPDs, transforming them into uracil and thymidine, respectively.
Error-free replication of the deaminated CPDs by DNA polymerase
η
then passes on C>T
mutations to daughter cells [14]. The CPDs thereby cause skin cancer [15].
1.2. Sunscreens and Clothing Protect against UVR-Induced Mutagenesis
Active ingredients of sunscreens fall into two categories: inorganic (also known as
mineral or physical) and organic (also referred to as chemical). Inorganic ingredients include
zinc oxide (ZnO) and titanium dioxide (TiO
2
). New data suggest that these inorganic
compounds primarily absorb UV radiation within the UVB and short UVA wavelengths and
reflect radiation in the long UVA and visible wavelengths [
16
]. Organic UVR filters contain
aromatic hydrocarbons that absorb photons in the UV spectrum and emit lower-energy,
longer wavelength photons and/or heat that do not damage the skin [
17
]. Both inorganic
and organic sunscreens prevent actinic keratoses (premalignant keratinocytic neoplasms)
and squamous cell carcinoma [
18
–
20
]. Sunscreen is also effective in prevention of basal cell
carcinoma and melanoma [
18
,
21
,
22
]. Furthermore, routine sunscreen application prevents
photoaging [17].
Clothing provides protection by scattering and absorbing UVR. Mouse models have
shown that sun-protective clothing can prevent skin cancer, but little human data exist in
the literature [
23
]. However, since UVR is a causal agent in skin cancer, protection with
clothing is likely to be dependent on the degree of protection provided from UVR. The
degree of protection depends on the color, material, fiber, yarn and fabric structure [
24
].
Fabric structure is one of the most important factors, with the least porous material pro-
viding the greatest protection [
25
–
27
]. Synthetic fabrics have demonstrated the highest
Cancers 2022,14, 542 3 of 19
UV protection [
28
–
30
]. Dark colors absorb more UVR and thus provide higher protection
than light colors [
29
,
31
–
33
]. Other factors that impact penetration of UVR through the
clothing include: stretch, wetness, wear (from use or washing), color loss (bleaching),
UVR-absorbing additives, and yarn morphology [
34
–
37
]. Although all clothing blocks
some degree of UVR, some studies suggest many commonly worn fabrics may provide
insufficient UVR protection [29,38,39].
1.3. Measures of UVR Protection
The sun protection factor (SPF)
rating traditionally used in sunscreen labeling is
measured by exposing small areas of skin of human subjects (Fitzpatrick skin
types I–III
)
to simulated solar radiation for varying durations. The smallest dose of UVR that pro-
duces visible, well-circumscribed redness on tested skin is called the minimal erythemal
dose (MED). SPF is the ratio of the MED with sunscreen uniformly applied at 2 mg/cm
2
(MEDprotected) to that of skin without sunscreen (MEDunprotected):
SPF =MEDprotected
MEDunprotected
(1)
Simply stated, SPF reflects the factor by which one can spend more time in the sun
without getting burned. For example, SPF 30 would theoretically allow someone who
would normally burn in 10 min to be exposed for 300 min before burning, assuming
constant incident solar UVR energy.
The ultraviolet protection factor (UPF)
rating traditionally used for clothing labeling
requires a laboratory spectrophotometer to measure UVR transmittance (the fraction of
UVR that is transmitted through the clothing). Although related, SPF and UPF are not
equivalent [
40
]. In contrast to SPF measurements (that utilize UVB-induced erythema as
the readout), UPF objectively measures all wavelengths of solar simulated light transmitted
through the clothing and then applies weighting constants to mathematically recapitulate
SPF testing. These constants (known as the erythemal effectiveness function and solar
spectral irradiance) heavily weight UPF toward the UVB wavelengths (Figure 1A) because
these are the primary wavelengths that induce erythema in the skin. The UPF of a garment
represents how much erythemally-weighted UVR is transmitted through the clothing. UPF
values are the ratio of erythemally-weighted UVR detected with or without a specimen
(clothing) between the light source and detector:
UPF =∑400nm
280nm Eλ×Sλ×∆λ
∑400nm
280nm Eλ×Sλ×Tλ×∆λ(2)
E
λ
is the relative erythemal spectral effectiveness, a constant that adjusts for the
ability of each wavelength (
λ
) to generate cutaneous erythema [
41
]. S
λ
is the solar spectral
irradiance (Wm
−2
nm
−1
), a constant that represents sun intensity at each wavelength at
noon in Albuquerque, New Mexico [
42
]. T
λ
is the average measured spectral transmittance
of the specimen and ∆λis the measured wavelength interval (nm).
Both of these measures represent the combined effect of incident dose and a biological
response. This biological response, slight reddening, is related to discomfort but it is blister-
ing sunburn that is related to skin cancer [
43
,
44
]. Neither SPF or UPF rating systems take
into consideration the fact that non-erythema-inducing UVR wavelengths are carcinogenic.
Nor do they take into consideration the fact that erythema and skin cancer have different
dose-dependencies. One measure currently used to address this deficit in evaluating the
performance of sunscreen is the critical wavelength.
The critical wavelength (CW, λc)
is calculated from the measured absorbance of a
sunscreen across the entire UV spectrum and is intended to provide an objective quantifi-
Cancers 2022,14, 542 4 of 19
cation of how well a sunscreen reduces exposure to both UVB and UVA wavelengths [
45
].
Absorbance (A), is the negative of the (base ten) logarithm of transmittance (T):
A(λ)=−log10[T(λ)] (3)
For example, at a given wavelength, a sunscreen or garment that blocks 90% of incident
UV radiation has an absorbance of 1 [
−
log (0.1)], while one that blocks 99% of incident UV
has an absorbance of 2 [
−
log (0.01)]. The transmittance of a sunscreen or textile is measured
with a spectrophotometer equipped with an integrating sphere, which allows capture of all
radiation that is diffusely scattered and transmitted through the sample. It is important to
note that absorbance, as used in the quantitative expressions described here, represents
more than just absorbed light; it also includes alternate means of radiation attenuation
including the reflection and/or scattering of incident light.
The critical wavelength is the wavelength below which 90% of the total absorbance
(A) of a sunscreen in the atmosphere-penetrating UVR region is contained (Figure 1B):
Zλc
290nm A(λ)dλ=0.9 Z400nm
290nm A(λ)dλ(4)
In other words, the absorbance of a particular sunscreen is measured as a function
of wavelength between 290–400 nm (UVB from 290–315 and UVA from 315–400). UVB-
specific sunscreen ingredients are not effective at preventing transmission in the UVA range,
producing absorbance curves that peak at the shorter end of the wavelength spectrum. In
contrast, UVA filters shift the absorbance curves to the right at the longer UVA wavelengths.
Sunscreens that block both UVA and UVB radiation have absorbance curves that extend
across the majority of the spectral region (Figure 1B). The area under the curve is summed
(integrated) from 290 nm to 400 nm. The critical wavelength is the wavelength at which
90% of the total area under the absorbance curve is reached. Therefore, a higher critical
wavelength indicates that the absorbance of a material is proportionally greater at longer
wavelengths and offers more relative protection from UVA radiation. However, a UVA-
specific agent with little absorbance in the UVB range could have a very high critical
wavelength yet inadequate protection against UVB or sunburn. Therefore, the critical
wavelength should never be interpreted in isolation and is only meaningful when SPF is
also taken into consideration. The United States Food and Drug Administration (FDA)
requires sunscreen to have a CW greater than 370 nm to be labeled as broad-spectrum [
46
].
% UV-Blocking.
The critical-wavelength requirement does not exist for garments.
Instead, some countries require sun-protective garments to have less than 5% transmittance
in the UVA region (T(UVA), Equation (5)) [47].
T(UVA)=∑400nm
315nm Tλ×∆λ
∑400nm
315nm ∆λ(5)
These values are often reported as % UVA blocking = 100%
−
T(UVA), where T(UVA)
is expressed as a percentage. Similarly, transmittance in the UVB region, T(UVB), is
determined using an analogous equation but evaluating wavelengths from 280 to 315 nm,
and % UVB blocking = 100% −T(UVB) where T(UVB) is expressed as a percentage.
In this paper, we compare the SPF,UPF, CW, and % UV-Blocking of commercial
sunscreens to those of modern sun-protective clothing. We follow this with a discussion of
the consequences of exposure of human skin to UVA radiation and summarize new data
on the mutagenic properties of visible light. We highlight the potential of sun-protective
clothing to offer superior protection from the underappreciated risks posed by these
wavelengths of solar radiation.
Cancers 2022,14, 542 5 of 19
Cancers2022,14,x 5of20
(A)UPF
(B)CW
Figure1.Ultravioletprotectionfactor(UPF)isprimarilyameasureofUVBprotectionwhereascrit‐
icalwavelength(CW)isameasureofthedegreeofbroad‐spectrumprotection.(A)UPFisamathe‐
maticalfunctiondesignedtorecapitulatesunprotectionfactor(SPF)fromalaboratorymeasure‐
mentoftransmittanceandisweightedtowardtheUVBportionofthespectrum.Left:Plotsofthe
erythemaleffectivenessfunction(E
λ
)andthesolarspectralirradiance(S
λ
)overtheUVRspectral
range.Right:TheproductofE
λ
andS
λ
hasapeakthatliespredominantly(75%)withintheUVB
range(280–315nm).VerylittleoftheUPFfunctioncomesfromwavelengthslongerthan360nm,
wheretheUVRintensityishighestbuttheerythemaleffectivenessisnearzero[48].(B)Visualrep‐
resentationoftheCWasthewavelengthbelowwhich90%ofthetotalabsorbance(areaunderthe
curve)intheUVRregioniscontained.Left:HypotheticalsunscreenthatprimarilyblocksUVBra‐
diationhasacriticalwavelengthbelowthe370nmthresholdrequiredbytheFDAtobelabeled
broad‐spectrum.Right:HypotheticalsunscreenwithimprovedUVAblockingperformancemeets
thebroad‐spectrumcriterion.AsunscreencouldmeettheCWcriterionof370nmwithoutcompre‐
hensivelyblockingUVAradiation.
2.MaterialsandMethods
2.1.Fabrics
Fourfabricsamples(Table1,Figure2)usedincommercialsun‐protectiveapparel
(ColumbiaSportswear,Portland,OR,USA)werechosenforthestudybecausetheyare
representativeofmodernsun‐protectivematerials:onenylonwovenandthreepolyester
Figure 1.
Ultraviolet protection factor (UPF) is primarily a measure of UVB protection whereas
critical wavelength (CW) is a measure of the degree of broad-spectrum protection. (
A
)UPF is
a mathematical function designed to recapitulate sun protection factor (SPF) from a laboratory
measurement of transmittance and is weighted toward the UVB portion of the spectrum. Left:
Plots of the erythemal effectiveness function (E
λ
) and the solar spectral irradiance (S
λ
) over the
UVR spectral range. Right: The product of E
λ
and S
λ
has a peak that lies predominantly (75%)
within the UVB range (
280–315 nm
). Very little of the UPF function comes from wavelengths longer
than 360 nm, where the UVR intensity is highest but the erythemal effectiveness is near zero [
48
].
(
B
) Visual representation of the CW as the wavelength below which 90% of the total absorbance
(area under the curve) in the UVR region is contained. Left: Hypothetical sunscreen that primarily
blocks UVB radiation has a critical wavelength below the 370 nm threshold required by the FDA to be
labeled broad-spectrum. Right: Hypothetical sunscreen with improved UVA blocking performance
meets the broad-spectrum criterion. A sunscreen could meet the CW criterion of 370 nm without
comprehensively blocking UVA radiation.
2. Materials and Methods
2.1. Fabrics
Four fabric samples (Table 1, Figure 2) used in commercial sun-protective apparel
(Columbia Sportswear, Portland, OR, USA) were chosen for the study because they are
representative of modern sun-protective materials: one nylon woven and three polyester
knit fabrics. The three knit fabrics include two different common knit structures, a pique
and an interlock. Of the two interlock knit fabrics, one includes a TiO
2
dot print covering
Cancers 2022,14, 542 6 of 19
about 30% of its surface. These white dots are present for heat mitigation, and work by
reflecting more solar radiation and emitting more thermal radiation than the underlying
polyester fabric [49]. These four fabrics are generally thinner and lighter than the ones for
which UPF and SPF data have been previously reported in the literature [
24
]. All fabrics
were dyed to be off-white.
Table 1.
Specifications of tested fabrics (
A
) and commercial sunscreens (
B
). FD = fully drawn,
DTY = drawn textured yarn, D = denier *, f = filaments. All knit fabrics are 28 gauge.
(A) Fabrics
Fabric Yarn(s) Areal Density
(g/m2)Thickness(mm)
Nylon Woven 70D(48f) ×160D(144f) 107 0.36
Polyester Pique Knit 75D(72f) ×75D(36f) FD 180 0.74
Polyester Interlock Knit 50D/72f FD DTY 90 0.48
Polyester Interlock Knit
w/TiO2dot print at 30%
surface coverage
50D/72f FD DTY 95 0.46
(B) Commercial Sunscreens
Sunscreen Labeled SPF Active Ingredients
Sunscreen A 30
Broad-spectrum
avobenzone 3%, homosalate 8%, octisalate 4.5%,
octocrylene 6%
Sunscreen B 50
Broad-spectrum
avobenzone 3%, homosalate 10%,
octisalate 4.5%, octocrylene 8%
* Denier is a measure of linear density, an indicator of yarn or filament size. More specifically, denier is the weight
in grams of 9000 m of yarn or filament.
Cancers2022,14,x 7of20
Figure2.Fourcommercialfabricswereselectedforstudy:(A)107‐gsm(g/m2)nylonwoven,(B)180‐
gsmpolyesterpiqueknit,(C)90‐gsmpolyesterinterlockknit,and(D)95‐gsmpolyesterinterlock
knitwithTiO2dotprintat30%surfacecoverage.Thesefabricsarecurrentlyusedinsun‐protective
apparel.Eachfabricisconstructedofmultifilamentsyntheticyarnsfrom50to160denier.Fabric
imagesweretakenusingaKeyenceVHX‐7000DigitalMicroscope(Itasca,IL,USA).Scalebaris250
μm.
2.2.Sunscreens
Twoorganic,broad‐spectrumsunscreens(SPF30andSPF50,Table1)wereselected
forcomparisonwiththefourfabrics.Thesunscreenswerethesamebrandandcontained
identicalactiveingredients:avobenzone,homosalate,octisalate,andoctocrylene.TheSPF
50sunscreenhadahigherpercentageofhomosalate(10%vs.8%)andoctocrylene(8%vs.
6%).TheseactiveingredientsarefourofthesixteenUVfilterslistedintheFDACodeof
FederalRegulations[50]andareacommoncombinationusedinmultiplebrandsofU.S.
sunscreens.Testswereperformedwithnewlyopened,unexpiredproducts.
2.3.InVitroUPFTesting
2.3.1.FabricUPF
UPFmeasurementsofthetextilefabricswereconductedasdescribedintheAmeri‐
canAssociationofTextileChemistsandColorists(AATCC)TestMethod183[48].Briefly,
eachdry,unstretchedfabricwasplacedinaUV‐2000SUltravioletTransmittanceAnalyzer
(LabsphereInc.,NorthSutton,NH,USA)tocapturediffusetransmittancefrom280to400
nm.Fiveuniquemeasurementsweretakenatdifferentsampleorientationsrotatedby45°
betweeneachmeasurement.UPFwascalculatedforthetransmissionspectrumofeach
sampleusingtheformulainEquation(2),andthenanaverageUPFandstandarddevia‐
tionwerecalculatedfromtheindividualUPFvalues[48].
Figure 2.
Four commercial fabrics were selected for study: (
A
) 107-gsm (g/m
2
) nylon woven,
(
B
)
180-gsm
polyester pique knit, (
C
) 90-gsm polyester interlock knit, and (
D
) 95-gsm polyester
interlock knit with TiO
2
dot print at 30% surface coverage. These fabrics are currently used in sun-
protective apparel. Each fabric is constructed of multifilament synthetic yarns from 50 to 160 denier.
Fabric images were taken using a Keyence VHX-7000 Digital Microscope (Itasca, IL, USA). Scale bar
is 250 µm.
Cancers 2022,14, 542 7 of 19
2.2. Sunscreens
Two organic, broad-spectrum sunscreens (SPF 30 and SPF 50, Table 1) were selected
for comparison with the four fabrics. The sunscreens were the same brand and contained
identical active ingredients: avobenzone, homosalate, octisalate, and octocrylene. The SPF
50 sunscreen had a higher percentage of homosalate (10% vs. 8%) and octocrylene (8% vs.
6%). These active ingredients are four of the sixteen UV filters listed in the FDA Code of
Federal Regulations [
50
] and are a common combination used in multiple brands of U.S.
sunscreens. Tests were performed with newly opened, unexpired products.
2.3. In Vitro UPF Testing
2.3.1. Fabric UPF
UPF measurements of the textile fabrics were conducted as described in the American
Association of Textile Chemists and Colorists (AATCC) Test Method 183 [
48
]. Briefly,
each dry, unstretched fabric was placed in a UV-2000S Ultraviolet Transmittance Analyzer
(Labsphere Inc., North Sutton, NH, USA) to capture diffuse transmittance from 280 to
400 nm. Five unique measurements were taken at different sample orientations rotated by
45
◦
between each measurement. UPF was calculated for the transmission spectrum of each
sample using the formula in Equation (2), and then an average UPF and standard deviation
were calculated from the individual UPF values [48].
2.3.2. Sunscreen UPF
UPF measurements of two commercial broad-spectrum sunscreens were conducted
using AATCC Test Method 183 [
48
]. Of note, many studies refer to spectrophotometric
testing of sunscreens as “
in vitro
SPF” and to erythema measurements of textiles on human
skin as “
in vivo
UPF.” To eliminate confusion, we will use the terms “sunscreen UPF” and
“fabric SPF” throughout. The two sunscreens were applied in accordance with International
Organization for Standardization (ISO) 2444 to UVR-transparent quartz slides at a density
of 2 mg/cm
2
. Additional testing was performed at a density of 1 mg/cm
2
to simulate
real-world consumer application [
51
]. Transmittance was measured using a Thermo Fisher
Evolution Bio260 spectrophotometer (Thermo Fisher Scientific, Waltham, MA, USA). To
account for non-uniformity in coating thickness, three slides were prepared for each sun-
screen SPF level and coating density. Ten measurements were taken in random positions
on each slide. UPF was calculated for each measurement, and the UPF is reported as the
mean and standard deviation of these measurements.
2.4. In Vivo SPF Testing
2.4.1. SPF of Fabrics
The fabric SPF on human skin of the four textile samples were measured by a third
party (AMA Laboratories, New City, NY, USA) using the standard procedure described
by the International SPF Test Method of COLlPA, CTFA, JCIA and CTFA-SA [
52
]. The
study was approved by the AMA Laboratories Internal Review Board. Briefly, the dose of
UVR was supplied by either a 150 or 300 watt Xenon Arc Solar Simulator (Solar Light Co.,
Philadelphia, PA, USA), each with a continuous emission spectrum from 290 to 400 nm.
Both were equipped with dichroic mirrors and a 1-mm Schott WG-320 filter to produce a
simulated solar UVA-UVB emission spectrum. These were also equipped with a 1-mm UG
11 filter to remove reflected heat as well as visible and infrared radiation.
A total of five healthy adult volunteers (ages 36 to 64 years) were selected by AMA
laboratories. Three volunteers (one from each Fitzpatrick Skin Type I, II, and III to maximize
the human variation studied) underwent SPF testing for each fabric [
53
] (
Tables S1 and S2
).
All individuals provided written informed consent. The bilateral infrascapular area of
each subject’s back was used as the test site. Test sites were cleaned with a dry cotton pad,
and rectangular areas of at least 30 cm
2
were demarcated. A minimum of five progressive
UVR doses were administered within this site to determine a subject’s minimal erythemal
dose on unprotected skin (MED
unprotected
). Each subject’s MED
unprotected
was defined as
Cancers 2022,14, 542 8 of 19
the shortest time of exposure (or lowest UVR dose required) that produced minimally
perceptible erythema at 16 to 24 h post exposure. A control sunscreen with standard SPF
15 or 16 was used as a verification technical control.
Once the MED
unprotected
had been determined, subjects returned to the lab for SPF
testing of the fabrics. The test fabric was secured closely to each subject’s skin without
stretching and using a thin layer of adhesive tape on the sample periphery to cover a
minimum area of 30 cm
2
. Based upon each subject’s previously determine MED
unprotected
,
the test areas were irradiated with a series of progressively higher UVR doses (minimum
of five). The subjects returned to the testing facility 16–24 h after UVR exposure for
determination of the MED of protected skin (MED
protected
) by a blinded evaluator. Each
fabric was tested on three subjects and the mean SPF was determined for each individual
fabric as the ratio of MEDprotected/MEDunprotected (Equation (1)).
2.4.2. SPF of Sunscreens
For the purposes of this study, the package label SPFs of the commercial sunscreens
were used. SPFs of commercial sunscreens in the U.S. are determined in accordance with
FDA regulations as described in the Code of Federal Regulations 21 [46].
3. Results
3.1. In Vivo SPF Values Are Higher for Fabrics Than Sunscreens
In vivo
SPF measurements of the fabrics ranged from 60 to 80, with the nylon woven
fabric having the lowest SPF and the polyester interlock knit having the highest SPF
(Table 2). All fabrics had a higher SPF than the SPFs on the sunscreen package labels.
Table 2.
Measured UPF,SPF, Critical Wavelength, UVA and UVB blocking capabilities of studied
fabrics and sunscreens. ** Each fabric SPF is the average of measurements across three subjects of
Fitzpatrick skin types I, II, and III to maximize the human variation studied. Each UPF quantity is an
average of 5 unique measurements per textile and 10 unique measurements per sunscreen at each of
the two concentrations.
Photoprotective
Modality SPF UPF Critical
Wavelength (nm)
UVA-
Blocking UVB-Blocking
Polyester Pique Knit 77 ±6 214 ±21 383 98.49 ±0.25% 99.76 ±0.03%
Nylon Woven 60 ±5 356 ±41 370 96.14 ±0.08% 99.93 ±0.02%
Polyester Interlock Knit 80 492 ±45 371 97.03 ±0.27% 99.95%
Polyester Interlock Knit
w/TiO2dot print at 30%
surface coverage
73 ±6 649 ±107 379 98.48 ±0.28% 99.95%
Sunscreen A (2 mg/cm
2
)
30 #16 ±12 371 74.05 ±10.17% 89.35 ±8.28%
Sunscreen A (1 mg/cm
2
)
30 #5.3 ±3.2 365 54.00 ±11.33% 76.45 ±13.46%
Sunscreen B (2 mg/cm
2
)
50 #31 ±19 373 82.13 ±8.71% 94.23 ±7.16%
Sunscreen B (1 mg/cm
2
)
50 #14 ±17 368 65.03 ±14.64% 84.79 ±14.42%
** Error indicated as standard deviations; when not indicated, the standard deviation of the measurements is
0. For critical wavelength, the minimum value is reported.
#
Commercial sunscreen SPFs were taken from the
package label.
3.2. In Vitro UPF Values Are Higher for Fabrics Than Sunscreens
In vitro
UPF measurements for all four fabrics exceeded 200 (Table 2). UPF values of
sunscreens demonstrated dose- and SPF-dependence, as expected. Sunscreen B (
SPF 50
)
applied at an areal density of 2 mg/cm
2
showed the greatest UPF (31
±
19), while Sunscreen
A (SPF 30) applied at 1 mg/cm2had the lowest UPF (5.3 ±3.2).
Cancers 2022,14, 542 9 of 19
3.3. All Fabrics Have CWs That Meet the Criteria for Broad-Spectrum Labeling
All four fabrics had critical wavelengths (CWs) greater than or equal to 370 nm, the
minimum value that the FDA requires for a sunscreen to be considered broad-spectrum
(Table 2). Both sunscreens exhibited a broad-spectrum CW of at least 370 nm at an areal
density of 2 mg/cm2, but not at 1 mg/cm2.
3.4. % UVB-Blocking Is Greater in Fabrics Relative to Sunscreens
All four textiles blocked > 99% of UVB (which equates to a transmittance < 1% in
the UVB region) with little difference detected between the four fabric types (Table 2).
Both sunscreens blocked UVB in a dose- and SPF-dependent manner (range of sunscreen
protection = 76–94%), with neither providing as much protection as the fabrics. The
fabrics exhibited consistently higher and less variable UVB blocking compared to the
two commercial sunscreens at both areal densities. The UVR spectra of the textiles and
sunscreens (Figure 3) show that all textiles had lower transmittance than the sunscreens
over the UVB wavelengths.
Cancers2022,14,x 10of20
Figure3.Transmittancecurvesofthetwocommercialsunscreensappliedat2mg/cm
2
and1mg/cm
2
comparedtocurvesofthefourfabricstested.Eachcurveisanaverageofmultiplemeasurements.
3.5.%UVA‐BlockingIsGreaterinFabricsRelativetoSunscreens
UVAblockingbythefabricsrangedfrom96%to98%,withthepolyesterfabricshav‐
ingslightlybetterperformancethanthenylonfabric(transmittance<4%intheUVAre‐
gion,Table2).AswithUVB,sunscreenUVAblockingincreasedwitharealdensityand
SPF,rangingfrom54%fortheSPF30formulationappliedat1mg/cm
2
to82%fortheSPF
50sunscreenappliedat2mg/cm
2
.ThebestsunscreenUVAblocker,SPF50appliedat2
mg/cm
2
,didnotblockUVAaswellasthelowestperformingfabric(nylon,at96%).All
fourtextileshadmuchlowerUVAtransmittancethanthesunscreens.Thetransmittance
ofalltestedsunscreensincreasedrapidlyintheUVAregionfrom380to400nm(Figure
3).
4.Discussion
ThefourtextilesinourstudyprovidedsuperiorUVRprotectionwhencomparedto
thetwocommercialsunscreenstested(Table2,Figure3).Allfourfabricssuccessfully
blockederythemogenicUVRatalevelbetterthanthesunscreens,asmeasuredbyUVB
transmittance,SPF,andUPFmetrics.Allfourfabricsweresuperiortothesunscreenswith
respecttoblockingfullspectrumUVR,asmeasuredbyUVAtransmittanceandCWmet‐
rics.TherewassubstantialdisparitybetweentheSPFandUPFvaluesdeterminedforboth
fabricandsunscreen.Despitepreviousreportstothecontrary[40],thisisnotsurprising
giventhefactthattheyaremeasuredindifferentways,usingtransmittanceofUVRto
calculateUPFincontrasttoinductionofadownstreamcutaneousreaction(erythema)to
calculateSPF.UPFisindirectlycalculatedusingamathematicweightingtosimulatethe
erythemogenicpotentialoftheUVR,whereasSPFdirectlymeasuresdevelopmentofery‐
themainresponsetoUVR.Inadditiontotheabsoluteperformanceoffabricsandsun‐
screens,therewassubstantialvariabilityofprotectionbysunscreensinourstudy,despite
greateffortsmadetoassureconsistency(Table2).Thisvariabilityislikelyduetothedif‐
ficultyinuniformlyapplyingsunscreenandhighlightsaninherentweaknessinsun‐
screenswithrespecttoinconsistentapplicationandthepropensityofsunscreenstowear
Figure 3.
Transmittance curves of the two commercial sunscreens applied at 2 mg/cm
2
and 1 mg/cm
2
compared to curves of the four fabrics tested. Each curve is an average of multiple measurements.
3.5. % UVA-Blocking Is Greater in Fabrics Relative to Sunscreens
UVA blocking by the fabrics ranged from 96% to 98%, with the polyester fabrics having
slightly better performance than the nylon fabric (transmittance < 4% in the UVA region,
Table 2). As with UVB, sunscreen UVA blocking increased with areal density and SPF,
ranging from 54% for the SPF 30 formulation applied at 1 mg/cm
2
to 82% for the SPF
50 sunscreen applied at 2 mg/cm
2
. The best sunscreen UVA blocker, SPF 50 applied at
2 mg/cm2
, did not block UVA as well as the lowest performing fabric (nylon, at 96%). All
four textiles had much lower UVA transmittance than the sunscreens. The transmittance of
all tested sunscreens increased rapidly in the UVA region from 380 to 400 nm (Figure 3).
4. Discussion
The four textiles in our study provided superior UVR protection when compared
to the two commercial sunscreens tested (Table 2, Figure 3). All four fabrics successfully
blocked erythemogenic UVR at a level better than the sunscreens, as measured by UVB
transmittance, SPF, and UPF metrics. All four fabrics were superior to the sunscreens with
Cancers 2022,14, 542 10 of 19
respect to blocking full spectrum UVR, as measured by UVA transmittance and CW metrics.
There was substantial disparity between the SPF and UPF values determined for both fabric
and sunscreen. Despite previous reports to the contrary [
40
], this is not surprising given the
fact that they are measured in different ways, using transmittance of UVR to calculate UPF
in contrast to induction of a downstream cutaneous reaction (erythema) to calculate SPF.
UPF is indirectly calculated using a mathematic weighting to simulate the erythemogenic
potential of the UVR, whereas SPF directly measures development of erythema in response
to UVR. In addition to the absolute performance of fabrics and sunscreens, there was
substantial variability of protection by sunscreens in our study, despite great efforts made
to assure consistency (Table 2). This variability is likely due to the difficulty in uniformly
applying sunscreen and highlights an inherent weakness in sunscreens with respect to
inconsistent application and the propensity of sunscreens to wear or wash off. Despite
these challenges, sunscreens remain an important tool of our armamentarium against skin
cancer when protective clothing is not an option.
4.1. Tailored Use of Fabrics and Sunscreens
In general, utilization of both photoprotective clothing and sunscreen offers improved
UV protection. However, some activities and climates make wearing photoprotective
clothing difficult or undesirable, and it is impractical to cover the entire body with clothing.
Similarly, sunscreens can be messy and difficult to apply and re-apply in proper amounts,
especially after vigorous exercise or water-related activities. Ideally, these two photoprotec-
tive methods can be combined and tailored for each person and for the outdoor activities in
which they are engaged. However, there are additional factors that should be considered
with respect to the use of clothing and sunscreen.
4.2. Limitations in the Use of Sunscreen for Photoprotection
We now know that radiation across the entire UVR spectrum damages DNA. A review
of the published absorbance spectra of active organic and inorganic sunscreens shows that
nearly all U.S. sunscreen ingredients provide little or limited protection at wavelengths
longer than 380 nm [
54
–
59
] (Figure 4). The curves in Figure 4reflect the transmission of
sunscreen ingredients at the maximum concentration allowed by the FDA. When applied at
high concentrations (25%), the inorganic compounds (ZnO and TiO
2
) do provide superior
protection across the UV spectrum compared to organic filters, but still show up to 20%
transmittance beyond 380 nm. However, very few sunscreens contain inorganic filters at
these high concentrations as they can be difficult to apply and have a chalky, cosmetically
less acceptable appearance. Most inorganic sunscreens on the market contain 10–20% ZnO
and 2–14% TiO2 [60]. It is also worth noting that eight broad-spectrum, organic UV filters
commonly used in other countries but not yet approved by the FDA also show an increase
in transmittance beyond 380 nm [61,62].
This gap in UVR protection is significant since long-wavelength UVA is capable of
producing reactive oxygen species and CPDs that can lead to skin cancer [
9
–
11
]. Although
the carcinogenic potential of UVB and UVC were first to be shown to produce mutagenic
CPDs and 6-4 photoproducts in DNA, a robust body of literature now exists supporting
the carcinogenic potential of UVA as well [
9
–
11
,
63
]. Recent studies also show that longer
UVA wavelengths (UVA1, 340–400 nm) induce more solar UV-signature mutations than
shorter UV wavelengths [
64
]. Lawrence and colleagues demonstrated that human skin
irradiated at 385 nm generated CPDs, which increased for 2 h and persisted for 24 h without
evidence of repair [
65
]. Additionally, irradiation of human skin with UVA1 and visible light
produces biomarkers of DNA damage in the form of increased TP53 and BCL-2 expression,
eliciting a DNA damage response without producing visible erythema [
63
]. Further, data
from Runger et al. suggest that UVA-induced CPDs may be more mutagenic than those
produced by UVB due to a lower and shorter-lived activation of protective cell cycle arrest
pathways [66].
Cancers 2022,14, 542 11 of 19
Cancers2022,14,x 11of20
orwashoff.Despitethesechallenges,sunscreensremainanimportanttoolofourarma‐
mentariumagainstskincancerwhenprotectiveclothingisnotanoption.
4.1.TailoredUseofFabricsandSunscreens
Ingeneral,utilizationofbothphotoprotectiveclothingandsunscreenoffersim‐
provedUVprotection.However,someactivitiesandclimatesmakewearingphotopro‐
tectiveclothingdifficultorundesirable,anditisimpracticaltocovertheentirebodywith
clothing.Similarly,sunscreenscanbemessyanddifficulttoapplyandre‐applyinproper
amounts,especiallyaftervigorousexerciseorwater‐relatedactivities.Ideally,thesetwo
photoprotectivemethodscanbecombinedandtailoredforeachpersonandfortheout‐
dooractivitiesinwhichtheyareengaged.However,thereareadditionalfactorsthat
shouldbeconsideredwithrespecttotheuseofclothingandsunscreen.
4.2.LimitationsintheUseofSunscreenforPhotoprotection
WenowknowthatradiationacrosstheentireUVRspectrumdamagesDNA.Are‐
viewofthepublishedabsorbancespectraofactiveorganicandinorganicsunscreens
showsthatnearlyallU.S.sunscreeningredientsprovidelittleorlimitedprotectionat
wavelengthslongerthan380nm[54–59](Figure4).ThecurvesinFigure4reflectthetrans‐
missionofsunscreeningredientsatthemaximumconcentrationallowedbytheFDA.
Whenappliedathighconcentrations(25%),theinorganiccompounds(ZnOandTiO
2
)do
providesuperiorprotectionacrosstheUVspectrumcomparedtoorganicfilters,butstill
showupto20%transmittancebeyond380nm.However,veryfewsunscreenscontain
inorganicfiltersatthesehighconcentrationsastheycanbedifficulttoapplyandhavea
chalky,cosmeticallylessacceptableappearance.Mostinorganicsunscreensonthemarket
contain10–20%ZnOand2–14%TiO2[60].Itisalsoworthnotingthateightbroad‐spec‐
trum,organicUVfilterscommonlyusedinothercountriesbutnotyetapprovedbythe
FDAalsoshowanincreaseintransmittancebeyond380nm[61,62].
Figure4.Transmittanceoforganicsunscreenfilters(testedinthisstudy)andinorganicsunscreen
filters(ZnOandTiO
2
).DatawereobtainedfromtheBASFsunscreensimulator[59]wherethemax‐
imumconcentrationallowablebytheFDA[46]wasusedtogenerateeachcurve.
Figure 4.
Transmittance of organic sunscreen filters (tested in this study) and inorganic sunscreen
filters (ZnO and TiO
2
). Data were obtained from the BASF sunscreen simulator [
59
] where the
maximum concentration allowable by the FDA [46] was used to generate each curve.
The high absorbance of textiles in the near UVA region raises the question of whether
there are biological effects of visible light against which textiles might also be protective.
UVR and visible light have been shown to generate reactive oxygen species (ROS) that
damage sensitive biomolecules in the skin. ROS produced by solar radiation in the UVB,
UVA, and visible wavelengths cause damage to DNA that is potentially mutagenic. Photons
in the UV region are the most efficient at producing ROS, but studies of the action spectrum
of sunlight indicate that more than 50% of free radicals, including ROS, arise from visible
light with wavelengths in the range of 400 to 700 nm [
67
]. The free radicals produced by
visible light have the same carcinogenic and ageing effects as their counterparts produced
by UV. The principal differences in the effects of various wavelengths of light on generation
of ROS in the skin are the chromophores that mediate radical production. Light-absorbing
chromophores in the skin include nucleic acids, aromatic amino acids, urocanic acid, NADH
and NADPH, cytochromes, riboflavins, porphyrins, melanin and its precursors, and
β
-
carotene [
68
]. These chromophores can act as photosensitizers that catalyze the generation
of ROS and reactive nitrogen species that, if not quenched by cellular antioxidant defenses,
can damage sensitive biomolecules such as DNA, RNA, proteins and lipids.
Blue light (400–500 nm) is known to generate pigmentary changes in human skin, par-
ticularly visible in persons with darker skin (Fitzpatrick phototypes III and IV). Irradiation
of the skin on the backs of healthy volunteers with 415 nm blue-violet light produced hyper-
pigmentation, independent of p53 activation, that persisted for months after exposure [
69
].
In subsequent mechanistic studies, the laboratory of Thierry Passeron showed evidence
that this effect is mediated by a dedicated sensor, opsin-3 (OPN3) which is expressed in
melanocytes [
70
]. Activation of melanogenesis downstream of OPN3 is calcium dependent,
activates the protein kinase CAMKII, and leads to the phosphorylation of the transcription
factor MITF and thus increased transcription of melanin synthesis enzymes tyrosinase
and dopachrome tautomerase (DCT). Blue light also facilitates the formation of a protein
complex that contains tyrosinase and DCT. This complex leads to sustained tyrosinase
activity that likely mediates the long-lasting hyperpigmentation that is observed in skin
type III and higher.
Cancers 2022,14, 542 12 of 19
Taken together, these data suggest that available sunscreens fail to protect against
wavelengths of radiation, both UVB and UVA, that produce CPD and 6-4 photoproducts,
which can result in mutations that drive carcinogenesis. In addition, there are hyperpigmen-
tation effects of visible light, also not blocked by current sunscreens, that are of significant
cosmetic concern to many individuals with darker skin. This makes protection from the
full spectrum of UV and visible radiation an important goal, but one that may be difficult to
achieve because of the strong cosmetic preference for transparent sunscreens. Sunscreens
that protect in the 380–700 nm region are opaque to the human eye, so most sunscreens lack
protection in the long UVA and visible spectrum. Importantly, photoprotective clothing
may represent a partial solution to this problem since opaque clothing effectively blocks
both UV and visible radiation.
4.3. Limitations in the Use of Clothing for Photoprotection
Few studies in the literature have directly compared the performance of UV-protective
clothing to sunscreen. In 2018, Coyne et al. reported the broad-spectrum protection afforded
by then-available commercial clothing [
71
]. Selected results from analysis of those data are
shown in Figure 5re-plotted as transmittance versus wavelength for comparison with the
four fabrics that we tested. Because this figure only includes fabrics, the upper limit of the
transmittance scale is 15%. In contrast, the transmittance scale in Figure 3, which includes
both fabrics and sunscreens, must extend to 100% to display the increasing transmittance,
and reduced protection, of the sunscreens beginning around 370 nm.
Cancers2022,14,x 13of20
sunscreenslackprotectioninthelongUVAandvisiblespectrum.Importantly,photopro‐
tectiveclothingmayrepresentapartialsolutiontothisproblemsinceopaqueclothing
effectivelyblocksbothUVandvisibleradiation.
4.3.LimitationsintheUseofClothingforPhotoprotection
FewstudiesintheliteraturehavedirectlycomparedtheperformanceofUV‐protec‐
tiveclothingtosunscreen.In2018,Coyneetal.reportedthebroad‐spectrumprotection
affordedbythen‐availablecommercialclothing[71].Selectedresultsfromanalysisof
thosedataareshowninFigure5re‐plottedastransmittanceversuswavelengthforcom‐
parisonwiththefourfabricsthatwetested.Becausethisfigureonlyincludesfabrics,the
upperlimitofthetransmittancescaleis15%.Incontrast,thetransmittancescaleinFigure
3,whichincludesbothfabricsandsunscreens,mustextendto100%todisplaytheincreas‐
ingtransmittance,andreducedprotection,ofthesunscreensbeginningaround370nm.
Figure5.TransmittancespectraofthefourfabricsdesignedforUVprotectiontestedinthisstudy
(orangeandpurplelines)comparedto“normal”clothingitemstestedbyCoyne,etal.(graylines).
ThedatafromCoyne,etal.weredigitized,convertedtotransmittanceandrepresenttheaverageof
the16measurementsasreportedintheoriginalstudy.Whitecottonanddarkgreycottonwere
GAP,Inc.100%cottonshirts.Thedenimwas69%cotton,30%polyester,1%spandexGAPjeans.
Polyesterreferstoa84%polyester,16%spandexCoolibarrashguard[71].
TheCoynedataplottedinFigure5aresummarizedinTable3.Thedenimjeans,dark
greycottonshirt,andpolyester/spandexphotoprotectiverashguardprovidedthemost
protection.Withtheexceptionofthewhitecottonshirt,allfabricsblocked>99%ofUVB,
blocked>96%ofUVA,andmettheminimumcriticalwavelength(370nm)tobeconsid‐
eredbroad‐spectrumprotection.Thefabricsinourstudyprovidecomparablebroad‐spec‐
trumprotection(Figure3,Table2)withoutrequiringdarkdyes.Sincelightercoloredfab‐
rics(suchasthosetestedinourstudy)generallyprovidetheleastprotectionforagiven
fabricstructure,dyesandpigmentsaddedfordeepercolorationwouldlendevenmore
UVRprotectionthanthatindicatedinTable2.AsshownintheCoynedata,acommon
whitecottonshirtdoesnottypicallyprovideasmuchUVRprotection(UPF=9,Table3)
asadarkgreyshirtmadeofthesamematerial(UPF=98,Table3).Ontheotherhand,the
denimtestedintheCoynestudyprovidedevenbetterUVRprotection(UPF=2000,Table
3).WhilefabricweightsandthicknesseswerenotprovidedintheCoynestudy,denimis
Figure 5.
Transmittance spectra of the four fabrics designed for UV protection tested in this study
(orange and purple lines) compared to “normal” clothing items tested by Coyne, et al. (gray lines).
The data from Coyne, et al. were digitized, converted to transmittance and represent the average of
the 16 measurements as reported in the original study. White cotton and dark grey cotton were GAP,
Inc. 100% cotton shirts. The denim was 69% cotton, 30% polyester, 1% spandex GAP jeans. Polyester
refers to a 84% polyester, 16% spandex Coolibar rash guard [71].
The Coyne data plotted in Figure 5are summarized in Table 3. The denim jeans, dark
grey cotton shirt, and polyester/spandex photoprotective rash guard provided the most
protection. With the exception of the white cotton shirt, all fabrics blocked > 99% of UVB,
blocked > 96% of UVA, and met the minimum critical wavelength (370 nm) to be considered
broad-spectrum protection. The fabrics in our study provide comparable broad-spectrum
protection (Figure 3, Table 2) without requiring dark dyes. Since lighter colored fabrics
Cancers 2022,14, 542 13 of 19
(such as those tested in our study) generally provide the least protection for a given fabric
structure, dyes and pigments added for deeper coloration would lend even more UVR
protection than that indicated in Table 2. As shown in the Coyne data, a common white
cotton shirt does not typically provide as much UVR protection (UPF = 9, Table 3) as a dark
grey shirt made of the same material (UPF = 98, Table 3). On the other hand, the denim
tested in the Coyne study provided even better UVR protection (UPF = 2000, Table 3).
While fabric weights and thicknesses were not provided in the Coyne study, denim is
typically heavier and darker than fabrics used for shirts. Thus, the Coyne data additionally
demonstrate that sufficiently heavy and dark fabrics, such as denim, will effectively block
UVR. The primary challenge for textile engineers is to provide outstanding UVR protection
in garments using fabrics that are lightweight and air permeable (attributes that are linked
to comfort in hot environments), thereby increasing the likelihood that a person would
choose clothing for photoprotection.
Table 3. UV-protective measurements of textiles from the literature [66] *.
Textile Fabrics UPF Critical Wavelength (nm) UVA Blocking UVB Blocking
White Cotton 9 389 91.7% 89.9%
Dark Grey Cotton 98 389 98.8% 99.1%
Denim 2000 389 100% 100%
Polyester 721 387 99.0% 100%
*UPF and critical wavelength shown are the values reported in Coyne et al., the UVA and UVB blocking is
calculated from the digitized average of the measurements.
4.4. Limitations of Current Photoprotection Metrics
Our data and that of Coyne, et al. also demonstrate that CW alone does not provide
a useful characterization of UVR protection. The white cotton fabric exhibits a critical
wavelength of 389 nm (Table 3), which technically meets the FDA definition of broad-
spectrum protection for a sunscreen. However, the same fabric has a UPF rating of 9 and
the actual protection provided across wavelengths is the lowest of all of the fabrics in this
comparison. The % UVA and UVB blocking values, 91.7% and 89.9%, respectively, are
better indicators of the minimal level of broad-spectrum protection provided by this white
cotton shirt.
Additionally, the specific shape of the UV transmittance curve can generate misleading
results for measurements of SPF,UPF and CW. In the case of materials that exhibit UV
transmission that increases rapidly through the UVA region, it is possible for a sunscreen
or a garment to provide poor UV protection despite having a seemingly adequate SPF,
UPF and CW. We illustrate this concept in Figure 6and Table 4. The solid curve represents
the measured transmittance of Sunscreen B applied at 2 mg/cm
2
, which has a labeled SPF
of 50 but a measured UPF of 31. The dashed curve is a hypothetical sunscreen with a
similar transmittance shape profile to Sunscreen B, but modified to achieve a UPF of 50.
One can conceptualize this shift as a person applying sunscreen at a higher areal density
than the recommended 2 mg/cm
2
(which is much higher than that typically applied by
consumers [
51
]). Although the hypothetical dashed curve now represents a UPF value of
50, and maintains a broad-spectrum CW of 374 nm, this “new” sunscreen still only blocks
87% of UVA, which is considered inadequate relative to the 95% UVA blocking criteria
used by some countries for sun-protective clothing. As this example demonstrates, the
combination of UPF and UVA blocking may provide more suitable measures for broad-
spectrum protection. Numerous jurisdictions, including the European Union, require this
combination as an indication of broad-spectrum protection for garments [47].
Cancers 2022,14, 542 14 of 19
Cancers2022,14,x 15of20
Figure6.Illustrationofthelimitationsofcurrentmeasuresofsunprotection.Thesolidcurveshows
themeasuredtransmittanceofSunscreenBappliedat2mg/cm
2
,whichhasaSPFratingof50but
hadameasuredUPFofonly31.Thedashedcurvewasgeneratedusingashiftingfunctiontosimu‐
lateatransmittancecurvewithanaverageUPFof50.Forboththemeasuredandsimulatedcurve,
therapidincreaseintransmittanceintheUVAregionrepresentsreducedprotectionfromUVAra‐
diation.
Table4.DatafromShiftingSunscreenBTransmittanceCurvetoSimulateUPF=50.
#
CommercialsunscreenSPFsweretakenfromthepackagelabel.
4.5.LimitationsofthisStudy
Oursmallsamplesizeanduseofonlyonebrandofcommercialorganicsunscreen
maylimitgeneralizability,althoughmostbrandsselectfromthesameingredientlist.Our
studydidnotdirectlytestinorganicUVfilters,butthetransmissioncurvesgeneratedus‐
ingtheBASFsunscreensimulator[59](Figure4)showthatZnOandTiO
2
demonstrateup
to20%transmittancebeyond380nm.ThehighconcentrationsofZnOandTiO2required
toachieveadequateUVAprotectionmayresultinasunscreenthatcanbedifficulttoapply
andhaveachalky,cosmeticallylessacceptableappearance.Themethodweusedtode‐
terminetheUPFofsunscreenshadlimitationsincludingvariabilityinsunscreenapplica‐
tionontheslideandtheslide’sdifferingpropertiesandstructurecomparedtohuman
skin.ChallengesposedbyinvitroUPFtestingofsunscreenshavebeendemonstratedin
priorstudies,andtodate,noinvitroUPFtestforsunscreenshasbeenapproveddueto
difficultyingeneratingreproducibleandreliableresultsfromlabtolab[72,73].
SunscreenUPFSPFCriticalWavelength
(nm)
UVA
BlockingUVBBlocking
SunscreenB(2mg/cm
2
)31±1950
#
37382.13±8.71%94.23±7.16%
ShiftedSunscreenB 50±30‐ 37486.70±5.66%96.75±4.03%
Figure 6.
Illustration of the limitations of current measures of sun protection. The solid curve shows
the measured transmittance of Sunscreen B applied at 2 mg/cm
2
, which has a SPF rating of 50 but
had a measured UPF of only 31. The dashed curve was generated using a shifting function to simulate
a transmittance curve with an average UPF of 50. For both the measured and simulated curve, the
rapid increase in transmittance in the UVA region represents reduced protection from UVA radiation.
Table 4. Data from Shifting Sunscreen B Transmittance Curve to Simulate UPF = 50.
Sunscreen UPF SPF Critical
Wavelength (nm)
UVA
Blocking UVB Blocking
Sunscreen B (2 mg/cm
2
)
31 ±19 50 #373 82.13 ±8.71% 94.23 ±7.16%
Shifted Sunscreen B 50 ±30 - 374 86.70 ±5.66% 96.75 ±4.03%
#Commercial sunscreen SPFs were taken from the package label.
4.5. Limitations of This Study
Our small sample size and use of only one brand of commercial organic sunscreen
may limit generalizability, although most brands select from the same ingredient list. Our
study did not directly test inorganic UV filters, but the transmission curves generated using
the BASF sunscreen simulator [
59
] (Figure 4) show that ZnO and TiO
2
demonstrate up to
20% transmittance beyond 380 nm. The high concentrations of ZnO and TiO
2
required to
achieve adequate UVA protection may result in a sunscreen that can be difficult to apply and
have a chalky, cosmetically less acceptable appearance. The method we used to determine
the UPF of sunscreens had limitations including variability in sunscreen application on the
slide and the slide’s differing properties and structure compared to human skin. Challenges
posed by
in vitro
UPF testing of sunscreens have been demonstrated in prior studies, and to
date, no
in vitro
UPF test for sunscreens has been approved due to difficulty in generating
reproducible and reliable results from lab to lab [72,73].
The SPF and UPF measurements were made under controlled laboratory conditions.
These do not account for the real-world photodegradation of sunscreen UV filters, or the
changes in performance due to the known decrease in areal density of the sunscreens as
Cancers 2022,14, 542 15 of 19
a consequence of friction, sweating, or water exposure [
74
,
75
]. In contrast, real-world
performance of textiles is likely superior in most situations. In our study, fabrics were
taped directly to the skin instead of suspended above the skin. On-skin testing has been
reported to drastically reduce SPF in fabrics due to the incident UVR passing directly
through the open parts of the fabric structure [
76
,
77
]. Although the SPF of the fabrics tested
may represent a “worst-case” scenario, all SPFs exceeded 60.
5. Conclusions
In our study, we demonstrate that the four tested fabrics provided superior UVB, UVA,
and overall broad-spectrum protection when compared to two commercial sunscreens.
These data, coupled with mounting concerns regarding sunscreen ingredients and excipi-
ents (including biological impacts [
78
], potential environmental harms [
79
], and difficulty
to apply correctly [
51
]), underscore that clothing should be considered the cornerstone of
UV protection. Nevertheless, sunscreen remains an important modality for UV protection,
especially on areas of the body such as the face and hands were where clothing may be
impractical. In the future, the most effective and widely adopted strategies will likely
incorporate both photoprotective clothing and sunscreens with absorbances extending into
the visible light range.
Photoprotection modalities, and their regulatory labeling, are imperfect and must
evolve with our understanding of the mutagenic potential of solar radiation beyond that
of UVB: erythema is not the only biologically relevant endpoint and may not be the
endpoint most closely associated with carcinogenesis. To provide comprehensive protection
from skin cancer, photo-ageing, and hyperpigmentation, strategies that impede the entire
spectrum of potentially damaging solar light are necessary. A better future metric of
photoprotection might simultaneously assess total transmittance across the entire spectrum
of radiation and then mathematically adjust for the known rate of mutations generated at
each wavelength.
Supplementary Materials:
The following supporting information can be downloaded at: https:
//www.mdpi.com/article/10.3390/cancers14030542/s1, Table S1: Inclusion and exclusion criteria
of subjects undergoing
in vivo
SPF testing of fabrics. Table S2: Characteristics of the individuals
undergoing in vivo SPF testing of fabrics.
Author Contributions:
Conceptualization, D.M.A. and H.W.B.; methodology, D.M.A. and H.W.B.;
software, M.A. and D.M.A.; validation, M.A. and D.M.A.; formal analysis, M.A., D.M.A. and H.W.B.;
investigation, D.M.A., H.W.B., R.A.D., T.C. and J.B. (Jennifer Beem); resources, H.W.B.; data curation,
M.A., T.P.S., D.M.A. and R.A.D.; writing—original draft preparation, E.G.B., J.B. (Joshua Bezecny),
D.M.A., H.W.B., J.B. (Jennifer Beem), D.E.B., P.B.C. and S.A.L.; writing—review and editing, E.G.B.,
J.B. (Joshua Bezecny), M.A., D.M.A., H.W.B., R.A.D., J.B. (Jennifer Beem), D.E.B., R.K., P.B.C. and
S.A.L.; visualization, M.A. and D.M.A.; supervision, H.W.B.; project administration, D.M.A. and
H.W.B.; funding acquisition, H.W.B. All authors have read and agreed to the published version of
the manuscript.
Funding:
The Columbia Sportswear Company provided funding for the data collection and portions
of the analysis. The OHSU Department of Dermatology and War on Melanoma
TM
provided salary
support for the OHSU investigators.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement:
Informed consent was obtained from all subjects involved in the study.
Data Availability Statement:
The original data presented in this study are available in the text and
supplementary figures. Figure 5was generated using data available from Coyne et al. [
71
]. Figure 6
was generated using the publicly available BASF sunscreen simulator: https://sunscreensimulator.
basf.com/Sunscreen_Simulator [59].
Cancers 2022,14, 542 16 of 19
Conflicts of Interest:
E.G.B. has no relevant conflicts to declare; J.B. (Joshua Bezecny) has no rele-
vant conflicts to declare; M.A. works at Exponent Inc., a consulting firm contracted by Columbia
Sportswear Company to assist with the measurements and data analysis; T.P.S. works at Exponent
Inc., a consulting firm contracted by Columbia Sportswear Company to assist with the measurements
and the data analysis; D.M.A. works at Exponent Inc., a consulting firm contracted by Columbia
Sportswear Company to assist with the measurements and the data analysis; H.W.B. is an employee
of Columbia Sportswear Company; R.A.D. was employed by Columbia Sportswear Company at the
time of this project; T.C. is an employee of Columbia Sportswear Company; J.B. (Jennifer Beem) is an
employee of Columbia Sportswear Company; D.B. has no relevant conflicts to declare; R.K. has no
relevant conflicts to declare; P.B.C. has no relevant conflicts to declare; S.A.L. has no relevant conflicts
to declare.
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