This article is published as part of a themed issue of
Photochemical & Photobiological Sciences on
Topical and systemic photoprotection
Published in issue 4, 2010
Behaviour and measurement
Chronic sun damage and the perception of
age, health and attractiveness, P. J. Matts and
B. Fink, Photochem. Photobiol. Sci., 2010, 9, 421
Knowledge, motivation, and behavior patterns
of the general public towards sun protection,
J. M. Goulart and S. Q. Wang, Photochem.
Photobiol. Sci., 2010, 9, 432
Molecular modifications of dermal and
epidermal biomarkers following UVA
exposures on reconstructed full-thickness
human skin, M. Meloni et al., Photochem.
Photobiol. Sci., 2010, 9, 439
In vitro tools for photobiological testing:
molecular responses to simulated solar UV of
keratinocytes growing as monolayers or as
part of reconstructed skin, L. Marrot et al.,
Photochem. Photobiol. Sci., 2010, 9, 448
Comparison between UV index measurements
performed by research-grade and consumer-
products instruments, M. P. Corrêa et al.,
Photochem. Photobiol. Sci., 2010, 9, 459
Ultraviolet filters, N. A. Shaath, Photochem.
Photobiol. Sci., 2010, 9, 464
The long way towards the ideal sunscreen—
where we stand and what still needs to be
done, U. Osterwalder and B. Herzog, Photochem.
Photobiol. Sci., 2010, 9, 470
Percutaneous absorption with emphasis on
sunscreens, H. Gonzalez, Photochem. Photobiol.
Sci., 2010, 9, 482
In vitro measurements of sunscreen
protection, J. Stanfield et al., Photochem.
Photobiol. Sci., 2010, 9, 489
Human safety review of “nano” titanium
dioxide and zinc oxide, K. Schilling et al.,
Photochem. Photobiol. Sci., 2010, 9, 495
Sunscreens and occupation: the Austrian
experience, H. Maier and A. W. Schmalwieser,
Photochem. Photobiol. Sci., 2010, 9, 510
UVA protection labeling and in vitro testing
methods, D. Moyal, Photochem. Photobiol. Sci.,
2010, 9, 516
Sunscreens: the impervious path from theory
to practice, P. U. Giacomoni et al., Photochem.
Photobiol. Sci., 2010, 9, 524
Dose-dependent progressive sunscreens. A
new strategy for photoprotection?, A. Gallardo
et al., Photochem. Photobiol. Sci., 2010, 9, 530
The FDA proposed solar simulator versus
sunlight, R. M. Sayre and J. C. Dowdy,
Photochem. Photobiol. Sci., 2010, 9, 535
How a calculated model of sunscreen film
geometry can explain in vitro and in vivo SPF
variation, L. Ferrero et al., Photochem. Photobiol.
Sci., 2010, 9, 540
Filter–filter interactions. Photostabilization,
triplet quenching and reactivity with singlet
oxygen, V. Lhiaubet-Vallet et al., Photochem.
Photobiol. Sci., 2010, 9, 552
Mechanistic insights in the use of a
Polypodium leucotomos extract as an oral and
topical photoprotective agent, S. Gonzalez et
al., Photochem. Photobiol. Sci., 2010, 9, 559
Vitamin D-fence, K. M. Dixon et al., Photochem.
Photobiol. Sci., 2010, 9, 564
UV exposure and protection against allergic
airways disease, S. Gorman et al., Photochem.
Photobiol. Sci., 2010, 9, 571
Photoprotective effects of nicotinamide, D. L.
Damian, Photochem. Photobiol. Sci., 2010, 9, 578
The two faces of metallothionein in
carcinogenesis: photoprotection against UVR-
induced cancer and promotion of tumour
survival, H. M. McGee et al., Photochem.
Photobiol. Sci., 2010, 9, 586
Dietary glucoraphanin-rich broccoli sprout
extracts protect against UV radiation-induced
skin carcinogenesis in SKH-1 hairless mice, A.
T. Dinkova-Kostova et al., Photochem. Photobiol.
Sci., 2010, 9, 597
Mice drinking goji berry juice (Lycium
barbarum) are protected from UV radiation-
induced skin damage via antioxidant
pathways, V. E. Reeve et al., Photochem.
Photobiol. Sci., 2010, 9, 601
Oestrogen receptor-β signalling protects
against transplanted skin tumour growth in
the mouse, J.-L. Cho et al., Photochem.
Photobiol. Sci., 2010, 9, 608
PERSPECTIVE www.rsc.org/pps | Photochemical & Photobiological Sciences
Chronic sun damage and the perception of age, health and attractiveness
Paul J. Matts*aand Bernhard Finkb
Received 14th November 2009, Accepted 28th December 2009
First published as an Advance Article on the web 11th February 2010
Young and healthy-looking skin is a feature that is universally admired and considered attractive
among humans. However, as we age, skin condition deteriorates due to a variety of intrinsic and
extrinsic factors determined not only by genetics and physiological health but also by behaviour and
lifestyle choice. As regards the latter, cumulative, repeated exposure to solar ultraviolet radiation (UVR)
is linked intrinsically to the induction of specific types of skin cancer and the expression of cutaneous
damage markers responsible for the majority of the visible signs of skin ageing. Here we review
empirical evidence for skin-specific effects of chronic UVR exposure and relate it to perception of
visible skin condition. In contrast to other dermatological accounts, we stress an evolutionary
psychology context in understanding the significance of age-related changes in visible skin condition in
human social cognition and interaction. We suggest that the “marriage” of the scientific fields of skin
biology and evolutionary psychology provides a modern, powerful framework for investigating the
causes, mechanisms and perception of chronic sun damage of skin, as it explains the human obsession
with a youthful and healthy appearance. Hence, it may be that these insights bring true emotional
impetus to the adoption of sun protection strategies, which could conceivably impact skin cancer rates
in coming years.
Skin “ageing” is defined by the normal process of chronological
ageing super-imposed by the process of so-called “extrinsic”
ageing, mediated by a variety of exogenous factors. While the
former is a universal human constant, the latter is determined
largely by behaviour and lifestyle choice. In this context, there
deleterious dermatological events. Acute exposure of unprotected
skin to solar UVR causes numerous physiological effects, the
most obvious of which is sunburn.1Chronic effects from repeated
exposure to solar UVR include specific types of skin cancer2,3and
a myriad of degenerative events responsible for the majority of
the visible signs of skin ageing (“photoageing”);4,5this article is
concerned with the latter.
Recent years have seen a very rapid increase in knowledge
concerning the etiology, epidemiology and prevention of chronic
solar UVR damage (for reviews see ref. 3, 6, and 7). According
to a recent survey of over 1000 women each in Germany, UK
and the USA (Fig. 1a; results on file at Procter & Gamble), self-
perceived facial skin ageing increases progressively over time and,
by the fifth decade, over half reported visible signs of photoageing
in their own skin (wrinkling and hyper-pigmented spots). In the
same survey, 80–90% of women also believed that both daily
and past sun exposure or sunburn were contributing factors to
older-looking skin (Fig. 1b). The message that exposure to solar
UVR damages the appearance of skin is, therefore, clear and
aThe Procter & Gamble Company, London Innovation Centre, Whitehall
1784 474508; Tel: +44 1784 474454
bDepartment of Sociobiology/Anthropology, University of Goettingen, D-
37077, Goettingen, Germany
apparently understood. Thus, it is interesting that, whereas 80–
90% of those women surveyed reported the use of sunscreens,
only 20–50% reported use of a sunscreen while sun-bathing, while
In other words, whilst acknowledging the undesirable, visible skin
effects of cumulative, chronic solar UVR exposure, the majority
of women do not take steps to moderate this phenomenon.
The “marriage” of skin biology and evolutionary
These survey data sit uncomfortably alongside the results of
recent and on-going research conducted in the rapidly growing
field of evolutionary psychology,8,9which provides empirical
evidence that human physical appearance (and “attractiveness”
in particular) has significant influence on social interaction and
as attractive11,13,14and that physical attractiveness is an important
criterion for human mate selection.15In fact, the perception of
facial attractiveness seems to be remarkably consistent, regardless
of race, nationality, or age.16It should not be surprising, therefore,
looking skin.17,18An improvement in facial skin appearance is
accomplished relatively easily by the use of make-up,19–21although
there is a modern trend toward the use of more invasive cosmetic
“procedures”, including chemical peels, the use of “fillers” and
the injection of Botulinum toxin.22Of course, while these treat-
ments are aimed at existing skin conditions, primary prevention
would seem to be the better option, which makes the attitudes
toward prophylaxis using sunscreens reported above all the more
This journal is © The Royal Society of Chemistry and Owner Societies 2010Photochem. Photobiol. Sci., 2010, 9, 421–431 | 421
different age groups recognising the appearance of wrinkles and hyper-pigmented spots in their own facial skin. (b) Percentage of women believing that
daily and past sun exposure were contributing factors to older-looking skin. (c) Percentage of women using sunscreen in different scenarios.
Results of a large-base survey conducted on women aged 18–65 years, 1000 each in the UK, Germany and the USA. (a) Percentage of women in
422 | Photochem. Photobiol. Sci., 2010, 9, 421–431This journal is © The Royal Society of Chemistry and Owner Societies 2010
Until recently, research into facial attractiveness focused pre-
dominantly upon the influence of symmetry, averageness and sex-
ually dimorphic traits on appearance (for reviews, see ref. 23–29).
All concluded that these physical characteristics probably reflect
an individual’s underlying genetic quality.30Facial symmetry, av-
erageness and sexually dimorphic features are, however, relatively
stable “macro” endpoints characterised by shape. Remarkably,
it is only recently that researchers in the field of evolutionary
psychology have started to consider facial skin itself as a visible
marker of an individual’s mate quality (in terms of health and
reproductive potential). In studies that presented isolated fields
of skin images to participants, it has been shown that people
are very sensitive to variation in apparent skin condition. For
example, when presenting small areas of skin cropped from the
completely independent of information relating to face shape.
Moreover, in an attempt to link the perceived attractiveness of
visible skin condition to the genetic quality of the viewer, Roberts
et al.32demonstrated that small areas of skin cropped from
facial images of men heterozygous at all three loci of the major
histocompatibility complex were judged by women to be both
healthier and more attractive than cropped skin images of men
who were homozygous at one or more of these loci.
Considered as a whole, it seems that there needs to be a far
greater understanding of the relationship between the known
skin-specific effects of chronic UVR exposure and the perception
of such effects, given the evidence which is now starting to
accumulate for the significance of skin in human social cognition
and interaction. To this end, in recent years we have been engaged
in a unique collaboration between the fields of skin biology,
its measurement and evolutionary psychology. Here we review
of age, health and attractiveness.
Photoageing and changes in visible skin condition
There is consensus among the scientific and medical communities
that chronic exposure to UVR in ordinary sunlight is a major
factor in the etiology of the progressive undesirable changes in
the appearance of skin.2,3,33–38Indeed, as simple within-subject
evidence of the phenomenon of photoageing, one need only
compare and contrast those areas of the body that receive a
relatively low lifetime dose of solar UVR (e.g., skin on the buttock
or volar forearm) to those receiving a corresponding higher dose
(e.g., skin on the face, neck or dorsal forearm). Fig. 2 provides an
example of this universal human observation.
The undesirable skin changes associated with chronic photo-
damage include: dryness, roughness, actinic keratoses, irregular
pigmentation (freckling/lentigines), wrinkling, elastosis, loss of
elasticity, dilated/tortuous blood vessels (telangiectasia), black-
heads (solar comedones) and sebaceous hyperplasia.4,37,39Various
dosimetry and modelling studies have demonstrated wide varia-
the obvious effects of geography and season, but also by the very
occupation, involvement in outdoor sports/recreation, choice of
holiday location, etc.).40–43That the skin changes mentioned above
skin (arms, upper chest/neck) and remarkably smooth, unblemished skin
within non-sun exposed areas within the same subject (image courtesy of
Professor Ronald Marks).
Juxtaposition of prominent chronic UVR damage on sun-exposed
are the result of such cumulative solar UVR dose is supported by
human survey and experimental data:
∑ Caucasian women with a high sun exposure history have a
higher incidence of chronic photodamage than women with a low
∑ Fair-skinned persons in areas of high insolation appear older
than age-matched cohorts in areas of lower insolation.46
∑ Fair-skinned individuals with high sun exposure appear
more aged than those with lower sun exposure within the same
∑ Areas of skin (face and neck) chronically exposed to low
levels of sunlight exhibit significant signs of photodamage in
dermal tissues compared to unexposed skin (inside upper arm
or abdomen) in the same individuals.38,48
Mechanisms of UVR-induced skin changes
Much insight into UVR-induced skin change has come from the
used for over 30 years as a model for human photoageing (see the
reviews in ref. 49–54). In this model, Bissett et al.55found that two
waveband regions were responsible for all histological, physical
and visible skin changes studied: 285–305 nm (predominantly
UVB) and 315–360 nm (predominantly UVA). With the exception
of skin sagging, shorter wavelengths of UVR were by far the
most efficient at inducing changes in the skin of hairless mice, i.e.
epidermal thickening, collagen damage, elastosis, and increases
in glycosaminoglycan levels. UVA can produce elastosis in the
radiation in chronic photodamage in man is not fully understood,
the potential of these wavelengths to cause skin change cannot be
ignored. The UVR in ordinary daylight is predominantly UVA,
which is forward-scattered into deeper skin layers compared to
Research in recent years has provided clearer insight into mech-
anisms for these effects at the molecular level. For example, Fisher
and co-workers,36,58–60conducted a series of experiments on the
In these studies, UVR up-regulated AP1-1 and NF-kB binding to
This journal is © The Royal Society of Chemistry and Owner Societies 2010 Photochem. Photobiol. Sci., 2010, 9, 421–431 | 423
DNA, known stimulators of matrix metalloproteinase (MMP) ex-
pression. Since metalloproteinases are known to degrade collagen
may be a primary mechanism mediating cutaneous photoageing.
These observations were supported further by Berneburg et al.61
While it appears that free radical damage is part of the normal
ageing process of the skin,6further free radical damage by
UVR-generated reactive oxygen species (ROS) probably plays
an important additional role in photoageing. Garmyn et al.62,63
proposed a damage model whereby UVR produces sufficient ROS
leading to oxidative damage of all skin components (proteins,
lipids and DNA), leading eventually to chronic visible change
in skin appearance. This hypothesis is supported by the work of
Scharffetter-Kochanek and colleagues, demonstrating apparent
ROS-involvement in the UVA-dependent induction of MMP-1,
MMP-2 and MMP-364–67and the involvement of hydroxyl radical
and lipid peroxidation intermediates in the UVB-induction of
MMP-1 and MMP-3.68,69
Relation of UVR-induced skin changes to appearance
How is this damage expressed in the skin components governing
appearance? First of all, it is well established that UVR can cause
changes in the relative composition and deposition pattern of the
dermal matrix proteins, collagen and elastin.70It is now known
that chronic exposure to sub-erythemal doses of UVR can cause
significant damage to collagen and elastin in hairless mice.49,50,71,72
These in vivo data are supported by the molecular mechanistic
studies of Fisher et al.36,58Wlaschek et al.38provide a compelling
case for a major role for ROS in the induction of changes in gene
expression pathways related to collagen degradation and elastin
accumulation. The most obvious and striking visible features of
this photodamage are skin wrinkling, roughness and sagging
(see Fig. 3), because the consequent loss of collagen density
reduces tensile strength while abnormal expression of elastin leads
to a significant reduction in the spring-like, elastic properties of
skin. The delicate surface structure of youth (“microrelief”, an
intricate isotropic arrangement of discrete primary and secondary
lines of 20–200mm in depth, intersecting at regular intervals to
form polygonal plateaus73), therefore, changes progressively such
that much of the finer secondary structure is lost and anisotropy
increases as the primary lines become the dominant feature.74–76
Superimposed upon these changes is the progressive development
of deeper invaginations of the skin surface, forming the structures
order of multiples of 100 mm in depth and develop particularly in
areas of both chronic sun exposure and repeated flexure (the peri-
orbital and naso-labial areas of the ageing face being classically
associated with these features). There is varying opinion over the
classification of wrinkles, although the four classes proposed and
reviewed by Pierard et al.76(type 1, atrophic; type 2, elastotic; type
3, expressional; type 4, gravitational) all have their ultimate root
in the compromised mechanics of atrophied dermal tissue, driven
primarily by chronic photodamage.
While this effect on skin mechanical properties is relatively well
characterised, it is not widely appreciated, however, that there
is also an impact on skin optics. As collagen is the primary
optical sub-surface scattering component within human skin, this
progressive reduction in collagen density drives an accompanying
reduction in intra-cutaneous bulk light transport and, therefore,
perceived youthful “glow” or “brightness”. Furthermore, chronic
UVR exposure also leads to abnormal distribution of the two
and haemoglobin. In young, healthy skin, both constitutive and
ing in a homogeneous distribution of the melanin chromophore in
both basal and sun-exposed sites.77–79Distribution is so homoge-
contrast. Despite the apparent age-related loss of melanogenic
activity in non-sun-exposed skin,80it is now well established that
accumulation of “mottled hyperpigmentation”, including “diffuse
hyperpigmentation” (the “whispy” dyspigmentation commonly
present on sun-exposed skin, not related to systemic disease),
and solar lentigines (Fig. 4).81–84The molecular mechanisms for
these phenomena are still not completely understood, although
Lentigos and diffuse hyper-pigmentation.
424 | Photochem. Photobiol. Sci., 2010, 9, 421–431 This journal is © The Royal Society of Chemistry and Owner Societies 2010
it is thought that ROS mediate heterogeneity in melanocyte
proliferation and activity.85Due to variation in epidermal melanin
content and melanosome distribution, pigmentary alterations
vary in their severity and manifestation among different ethnic
groups (reviewed in ref. 86 and 87). The net result is that the
process of photoageing produces localised concentration and an
with increased visible contrast.
Haemoglobin is confined to red blood cells within the rich
network of vessels of the dermal plexus. Whereas it is generally
accepted that intrinsic ageing produces a reduction in the super-
ficial horizontal capillary plexus,83,88–90once again the vasculature
of sun-exposed skin is markedly different. Photo-ageing results in
capillaries that are tortuous and dilated, producing a spectrum
of severity of telangiectasia (Fig. 5).70,91Within areas of chronic
sun exposure, the vessel wall appears to thicken as a result of
the peripheral addition of a layer of basement membrane-like
a reduction in density of the supportive, perivascular connective
tissue produces fragile vessel walls that are less able to support
the internal turgor of blood volume and external mechanical
stress. As a result of this mechanical failure, chronic dilation,
the formation of sinuses and galleries and, to a limited extent,
low-grade purpura, drive the progressive and classic appearance
of telangiectasia and “blotchiness” associated with ageing skin.
Importantly, once again, photo-ageing produces a steady accu-
mulation of local concentrations of this chromophore in human
Contrast sensitivity and perception of skin
How do these biological changes of skin relate to its perception?
Quite simply, we view the world through sensitive visible-light
meters (i.e., the human eye) and, therefore, the phenomenon of
“contrast sensitivity” is of critical importance when considering
skin. “Contrast” can be defined simply as a ratio of adjacent
luminance values and “contrast sensitivity” is a measure of how
faded or washed-out an image can become before it is no longer
distinguishable from a uniform field. It has been determined
experimentally that the minimum discernible difference in grey-
scale level that the human eye can detect is about 2% of full
brightness.95,96This outstanding contrast sensitivity allows us to
perceive the world around us in great detail; indeed, without
contrast, we would effectively be rendered blind. The human
eye, therefore, is drawn automatically to areas with high ratios of
adjacent luminance—in simple terms, we view the world through
edges created by contrast. Contrast sensitivity is a function of the
size and spatial frequency of the features in the image. However,
this is not a direct relationship as larger objects are not always
easier to see than smaller objects, due to reduced contrast. Visible
contrast is greatest, therefore, when both the ratio of adjacent
luminance values is high and when features that contain these
values are large.
In young skin, reflection from the skin surface is largely diffuse,
up “microrelief”, and this has been found to be predictive for
age and cumulative photodamage, so too is this natural “soft-
focus” effect, driving low-contrast optics. In ageing human skin,
such as “lines”, “furrows” and “wrinkles”.
Colour, however, also plays an important role in the per-
ception of age, health and attractiveness. It has already been
established that the process of intrinsic and extrinsic ageing drives
a steady accumulation of enlarging, localised concentrations of
the two coloured chromophores, melanin and haemoglobin. In
other words, independent of contrast formed by shape and/or
topography, localised concentration of chromophores in ageing
skin causes a significant increase in visible contrast, particularly
in sun-exposed areas such as the face.
Chronic solar UVR skin damage and perception of
age, health and attractiveness
It is a widespread notion that flawless skin is one of the most
universally desired human features.98,99Males in particular are
attracted to female skin which is free of blemishes, lesions,
eruptions, warts, cysts, tumors, acne, and hirsutism,99as such skin
signals youth and health and is, therefore, perceived as attractive.
However, even a cursory inspection of the literature reveals that
although human beauty “standards” have often been proclaimed,
the scientific evidence supporting the significance of human skin
in an evolutionary psychology context is actually scarce. Most
studies of facial attractiveness have investigated characteristics
traits (for reviews, see ref. 10, 24 and 28). It is thought that these
characteristics all pertain to health, leading to the conclusion
that humans have evolved to view certain bodily features as
attractive because they are displayed by healthy individuals.
Evolutionary psychologists argue that preferences for these traits
are adaptive because mating with individuals who display them
This journal is © The Royal Society of Chemistry and Owner Societies 2010Photochem. Photobiol. Sci., 2010, 9, 421–431 | 425
skin? Can it be added to this list of features that signal aspects of
significance in human mate selection?
Comparative studies in the animal kingdom provide evidence
that body surface and colour signals are important in sexual
selection. For example, feather and skin colouration is known
to influence sexual attractiveness in a wide variety of non-human
animals101and studies on pigmentation in birds have shown that
colour signals are linked to immuno-competence and health.102,103
Carotenoid-based colouration in birds affects mate choice104and
there is similar evidence for an association between colour display
and mate choice in other organisms, including butterflies,105fish106
and lizards.107The general finding is that males prefer more
sexual signals resulting in male preferences for certain females.
The evidence for the role of colouration from studies using non-
human primates is, perhaps, a little more intuitive. Waitt et al.108
report that female rhesus macaques preferred males with red
facial colouration and suggest that male colouration is a quality
cue. More recently, Setchell et al.109report an increase in facial
colouration of female mandrills, proportional with age, and argue
that colour, therefore, signals reproductive quality. If we follow
the phylogenetic tree, it seems plausible to argue that there may
be a link between visible skin condition and perception of quality
derived from skin in humans also.
In this light, it is worth considering the fact that dermatoses in
humans often reflect systemic physiological imbalance and may
thus be associated with reduced reproductive ability. For example,
an increase in androgens is responsible for symptoms expressed
through both fertility-related problems and characteristic dark
skin patches (acanthosis nigricans; for example, see ref. 110).
Skin condition and face perception
Fink, Grammer and Thornhill111showed that, in a sample of
young Caucasian women, facial skin affected male judgement of
facial attractiveness. By using an objective image segmentation
method that quantified contrast in facial skin images, they
found that homogeneous skin was perceived as most attractive.
However, in contrast to previous reports,112this study did not
find a male preference for women with paler skin. This may be
explicable in terms of a preference for sun-tanned skin and seems
reasonable also when considering the general skin colouration of
the American population the sample faces were selected from.18
More recently, evolutionary psychologists have made some
progress with the empirical investigation of visible skin condition
Fink, Grammer and Matts113found that variation in the homo-
geneity of female skin colour distribution can alter perception
of facial age by up to 20 years. This study used digital images
of faces that were standardized with respect to their form and
in which information relating to skin surface topography was
removed. Thus, they differed only with respect to the skin colour
distribution of the original images (Fig. 6). As significant variance
was observed with visual perception of facial age and judgements
of attractiveness, health and youth, this signal can only have
been due to changes in the homogeneity of visible skin colour
distribution—driven predominantly by chronic UVR exposure.
The remarkably high correlations between estimated age and
facial attributes observed suggest that human skin condition has a
affects mate preference. In addition, by using the same stimuli in
an eye-tracking study, Fink et al.114found not only that judgement
of visible skin colour distribution varies in correspondence to
local homogeneity of pigmentation, but that this variation also
selectively attracts the viewer’s attention. In accord with Fink,
Grammer and Matts,113shape- and topography-standardized
stimulus faces with even skin colouration were judged to be
younger, received higher attractiveness ratings, and received a
higher number of gaze fixations and longer dwell-time.
From these recent studies, it may be concluded that facial skin
ageing, with the dyschromia and decrease in bulk light reflection
characteristic of chronic UVR damage,79can be readily perceived
by men and women and, in consequence, affects our perception
of others. However, as in many studies of human attractiveness,
Examples of shape and topography-standardised stimuli with skin colour distribution as the only variable (from the study of Fink et al.).113
426 | Photochem. Photobiol. Sci., 2010, 9, 421–431This journal is © The Royal Society of Chemistry and Owner Societies 2010
these findings were based on perception of apparent differences
in visible skin condition in the context of whole faces. Thus, in
order to investigate the hypothesis that variation in judgement of
facial skin is indeed a matter of contrast sensitivity (which can
be quantified objectively), Matts et al.77studied the relationship
between perception of skin condition and homogeneity of chro-
mophore distribution. As the authors note, one shortcoming of
available psychobiological studies on the effect of skin condition
on facial perception and judgement is that, “to date, it appears
that a foundational approach to cutaneous optics has not yet been
considered”. We now have a variety of sophisticatedmathematical
models to explain the interaction of light with skin. A review
of these models reveals that normal human skin colouration
is driven overwhelmingly by only three components, namely
absorption (and associated spectral modification) by the melanin
and haemoglobin chromophores and sub-surface scattering by
collagen.115It follows, therefore, that the kaleidoscope of both
inter- and intra-individual skin colouration is derived solely from
unique blends of these three optical components. Understanding
how the expression and presentation of these molecules change
with age, therefore, is critical in understanding the changing
appearance of skin across a human lifetime.
Matts et al.,77therefore, investigated visual perception of
isolated fields of skin, cropped from images of female faces,
and related the perception of these images to (a) an objective
analysis of homogeneity of skin colouration and (b) to grey-scale
concentration maps of (eu)melanin and (oxy)haemoglobin in the
same image, obtained using non-contact SIAscope technology
(Fig. 7; see also ref. 77 and 116 for details). It was found
that homogeneity of unprocessed images correlated positively
with perceived age, health and attractiveness. Homogeneity of
melanin and haemoglobin chromophore maps was positively
and significantly correlated with that of unprocessed images and
negatively correlated with estimated age. Thus, skin colour homo-
geneity, driven directly by melanin and haemoglobin distribution,
influences perception of age, health and attractiveness.
However, facial skin age is influenced not only by dyschromia
and a loss of hygroscopicity and hydration (for example, see
topography cues on perception, Perrett et al.120used computer
graphics technology to derive untextured composite faces (via
age characteristics on perception of facial attractiveness. These
with the average biological age of the participants, suggesting
that skin topography cues do indeed affect age perception. While
such digitally-synthesised facial stimuli can be useful in testing
one’s response to certain facial characteristics, in reality visible
skin condition is comprised by a complex interaction of skin
colouration and skin surface topography. In order to investigate
the relative strength of topography and skin colouration cues in
influencing perception, Fink and Matts121systematically removed
skin colouration and topography cues in female facial images and
then investigated the perceived age and health of these stimuli.
It was found that skin colour and topography affect perception
of both age and health, but convey differential information
with regard to the strength of these effects. When skin colour
information was preserved but skin surface topography cues (such
as fine lines and wrinkles) were removed, the investigators noted
a decrease in the estimated age of female faces of about 10 years
compared to unmodified faces. In contrast, digital smoothing of
facial discolouration resulted in a decrease of perceived age of one
to five years. Female faces were judged youngest when these image
manipulations were combined, i.e. when both surface topography
cues were removed and skin colour was smoothed, resulting in a
decrease in perceived age of approximately 15 years.
affected perceived age, skin topography cues accounted for the
larger proportion of variation in age estimation, which supports
119). In an early attempt to study the effect of skin surface
This journal is © The Royal Society of Chemistry and Owner Societies 2010Photochem. Photobiol. Sci., 2010, 9, 421–431 | 427
of perceived health were obtained for stimulus faces with only a
smoothing of skin colour. An important conclusion of the study
by Fink and Matts121was that, although the dynamic range of the
estimated ages from this study indicated that visible facial colour
distribution can account for up to twenty years of apparent age,
independent of face shape and skin surface topography,113the
ecological validity of this observation may be questionable. In
normal ageing skin, intrinsic and extrinsic factors are responsible
for changes of pigmentation and skin surface topography, though
the latter are usually more pronounced in older individuals.117
Thus, in pre-menopausal women, and particularly those at college
age who comprise the majority of subjects in attractiveness
research, skin colouration may be more important with regard
to facial appearance than skin surface topography. In the older
sample used in the Fink and Matts study,121comprising women
aged 40+, removal of topography cues had a stronger effect on
facial age perception than skin colour smoothing (although the
visibility of both variables resulted in the greatest decrease in
perceived age). Even in the presence of topography cues, we
appear to be sensitive to skin colouration cues and relate them
to healthiness. In other words, in mature women, a diminution
of facial discolouration can result in a significant increase of
perceived health and, in turn, a concomitant increase in perceived
attractiveness. It may be that we are now starting to bring true
meaning to the previously unqualified notion of “growing old
Until recently, scientific attention has been focused, and rightly
so, on the more sinistereffects of chronic exposure to erythemally-
effective solar UVR, i.e. the induction of skin cancers. The World
Health Organization has estimated that, in the year 2000, up to
71000 deaths worldwide were attributable to UVR exposure.122
In developed Western countries, skin cancer rates continue to rise
dramatically. In the UK, for example, skin cancer is the most
common form of cancer, with at least 70000 new cases and 2300
deaths annually.123Despite wide and varied public information
campaigns mediated by word of mouth, mass media and the
internet, however, various data suggest that public perception of
the risk and severity of skin cancer remains low.124,125
As reviewed in this article, essentially the same erythemally-
effective wavelengths of solar UVR responsible for these cancers
also propagate a range of visible cutaneous damage endpoints,
the phenomenon of photoageing. In an attempt to translate these
events relating to photobiology into a concept understandable to
the non-expert layman, the term “premature ageing” has entered
the vernacular. Indeed, markets worldwide are already noting the
introduction of commercial sunscreens claiming additional bene-
spectrum protection), relating to the prevention of “premature
not enough to encourage the use of appropriate photoprotective
measures, perhaps alerting the consumer to the chronic effects of
solar UVR on her/his appearance may provide an incremental
call to action.
The emerging collaboration between the disciplines of biology
and evolutionary psychology is now starting to make sense of
the rather unsatisfactory term “premature ageing”, revealing the
often profound signalling value of these skin changes as regards
perceived age, health and attractiveness. It may be that the new
insights we are uncovering, which for the first time relate chronic
UVR skin damage markers to perception in a broader context,
bring true emotional impetus to protect and maintain one’s
appearance. If this is the case, it may not be unreasonable to
hypothesise that a resulting increased and more diligent use of sun
protective strategies, including sunscreens, would have an impact
on skin cancer rates in coming years.
Company, Cincinnati, USA, and the German Science Foundation
(DFG), grant number FI 1450-4-1, awarded to Bernhard Fink,
as well as through the Institutional Strategy of the University of
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