The Impact of Shampoo Wash Frequency on Scalp and Hair Conditions

Abstract

Background:
How frequently should the scalp and hair be cleansed? A dearth of objective data has led to confusion both among lay people and experts. Each extreme has potential detrimental effects: overcleaning may lead to surface damage while undercleaning may lead to buildup of harmful stimuli. This situation is complicated because both objective and subjective criteria are relevant to assess optimal cleaning.

Objectives:
The objective of this work was to combine epidemiological and treatment data with both objective and subjective end points to yield clear data to guide both the consumer and expert as to optimal scalp and hair cleaning practices.

Methods:
Two studies were conducted with Asian populations without any specific scalp pathologies. An epidemiological study was conducted as a function of natural wash frequency. This was combined with a controlled wash frequency study. In both cases, objective measures of hair and scalp condition were assessed. These were combined with self-assessments of all participants.

Results:
In the epidemiological study, it was observed that overall satisfaction with hair and scalp condition was achieved when washing 5-6 times per week. This was consistent for both objective and subjective end points. Controlled treatment likewise showed that a daily wash regimen was superior to once per week cleansing for all end points. No objective detrimental effects to hair at this level of cleansing were observed.

Conclusions:
Two different studies led to the same conclusion: higher wash frequency is both beneficial and more preferred to lower wash frequency among the Asian populations studied. Concerns related to "overcleaning" were unfounded both objectively and subjectively.

Full text

Clinical Investigations – Research Article
Skin Appendage Disord 2021;7:183–193
The Impact of Shampoo Wash Frequency
on Scalp and Hair Conditions
Supriya Punyani
a Antonella Tosti
b Maria Hordinsky
c Dawn Yeomans
d
James Schwartz
d
aThe Procter & Gamble Company, Singapore, Singapore; bDepartment of Dermatology and Cutaneous Surgery,
University of Miami, Miami, FL, USA; cDepartment of Dermatology, University of Minnesota, Minneapolis, MN, USA;
dThe Procter & Gamble Company, Mason, OH, USA
Received: September 28, 2020
Accepted: November 4, 2020
Published online: February 15, 2021
James Schwartz
The Procter & Gamble Company
8700 Mason-Montgomery Rd.
Mason, OH 45040 (USA)
schwartz.jr.2 @ pg.com
© 2021 S. Karger AG, Basel
karger@karger.com
www.karger.com/sad
DOI: 10.1159/000512786
Keywords
Shampoo frequency · Scalp · Hair · Oxidative stress ·
Epidemiological · Treatment
Abstract
Background: How frequently should the scalp and hair be
cleansed? A dearth of objective data has led to confusion
both among lay people and experts. Each extreme has po-
tential detrimental effects: overcleaning may lead to surface
damage while undercleaning may lead to buildup of harmful
stimuli. This situation is complicated because both objective
and subjective criteria are relevant to assess optimal clean-
ing. Objectives: The objective of this work was to combine
epidemiological and treatment data with both objective and
subjective end points to yield clear data to guide both the
consumer and expert as to optimal scalp and hair cleaning
practices. Methods: Two studies were conducted with Asian
populations without any specific scalp pathologies. An epi-
demiological study was conducted as a function of natural
wash frequency. This was combined with a controlled wash
frequency study. In both cases, objective measures of hair
and scalp condition were assessed. These were combined
with self-assessments of all participants. Results: In the epi-
demiological study, it was observed that overall satisfaction
with hair and scalp condition was achieved when washing
5–6 times per week. This was consistent for both objective
and subjective end points. Controlled treatment likewise
showed that a daily wash regimen was superior to once per
week cleansing for all end points. No objective detrimental
effects to hair at this level of cleansing were observed. Con-
clusions: Two different studies led to the same conclusion:
higher wash frequency is both beneficial and more preferred
to lower wash frequency among the Asian populations stud-
ied. Concerns related to “overcleaning” were unfounded
both objectively and subjectively. © 2021 S. Karger AG, Basel
Introduction
There are few questions in personal care that elicit
more debate than “How frequently should I use a sham-
poo?” The opinions can vary from one end of the spec-
trum (as infrequently as possible) to the other (daily). For
example, in one 3-month period, 2 relevant articles were
published in the New York Times – one suggesting hair
is washed too frequently [1] and the other suggesting the
exact opposite [2]. Consumers appear to be responding
more strongly to recommendations to reduce shampoo-

Punyani/Tosti/Hordinsky/Yeomans/
Schwartz
Skin Appendage Disord 2021;7:183–193
184
DOI: 10.1159/000512786
ing as declining shampoo wash frequency is observed in
industry habit and practice studies and documented in
the popular press [3, 4].
The reason for these divergent opinions is that little
objective data exists to facilitate informed decision-mak-
ing. For those recommending low wash frequency, the
most often cited reasons are beliefs that hair is damaged
due to surfactant-induced extraction of beneficial lipid
components and stimulation of excessive compensatory
scalp sebum production. Taken to the extreme, there are
those that recommend avoiding the use of shampoos al-
together; this has been colloquially termed “no poo.” At
the other end, those that recommend higher wash fre-
quencies usually assert the benefits of removing a wide
range of potentially detrimental “dirt” residues. This po-
sition is reinforced by acknowledging that scalp is just an
extension of the face, which is almost universally washed
at least daily.
The buildup of “dirt” on hair and scalp has multiple
origins: endogenous sources such as sebum excretion and
skin exfoliative processes as well as exogenous sources
such as certain hair treatment products, airborne pollu-
tion, and pollen as well as exposure to volatile materials
such as those arising from tobacco smoke. The covering
of the scalp by hair creates a unique skin surface micro-
environment that facilitates microbial growth (dark,
moist, and sebum rich), leading to a unique microbiome
[5]. These microbes use components of the “dirt” as food
sources which fuel their metabolic activity, enhancing
their impact on the underlying skin [6].
Existing Literature Relating Wash Frequency and
Scalp Condition
Decreased wash frequency results in longer accumula-
tion times for secreted sebum. Sebum begins to be chem-
ically altered as soon as it reaches the scalp surface; the
longer its residence time, the greater these modifications.
Specifically, modified sebum contains free fatty acids and
oxidized lipids, which are known to be irritating to skin
[6, 7].
Two extreme cases of low wash frequency have been
evaluated relative to scalp impact. An Antarctic research
team was monitored for changes in scalp microbe content
and resultant symptoms [8]; during the expedition, scalp
itch and flakes increased dramatically, which was also ac-
companied by a 2–3 order of magnitude increase in scalp
Malassezia levels. These same authors subsequently stud-
ied International Space Station astronauts [9] and found
a dramatic rise in Malassezia levels over time with them
as well.
Even in less-extreme low-wash-frequency situations,
impacts to scalp condition have been observed. In an ep-
idemiological work studying Caucasian, Chinese, and Af-
rican American individuals, lower shampoo wash fre-
quency was associated with a higher prevalence of scalp
issues such as dandruff [10]. Low wash frequency has also
been observed to result in increased prevalence of sebor-
rheic dermatitis in African Americans (AA) [11]. In a
treatment study of individuals having a normal habit of
low wash frequency and experiencing seborrheic derma-
titis or psoriasis, wash frequency was deliberately in-
creased, first with a cosmetic shampoo and then with a
scalp treatment product [12]. Increased wash frequency,
even if just using a cosmetic shampoo, resulted in de-
creased flaking, redness, itching, Malassezia amount, and
the level of inflammatory cytokines.
Sebum accumulation and itch severity was studied as
a function of time post-shampoo [13]. It was observed
that itch severity increased significantly during 72 h post-
shampoo, coincident with increases in sebum accumula-
tion, supporting the model that Malassezia metabolism
leads to the resultant accumulation of irritating stimuli
such as oxidized free fatty acids that initiate itch. Higher
scalp sebum levels have been shown generally to be re-
lated to the prevalence of scalp sensitivity [14], suggesting
a cause-and-effect relationship.
Existing Literature Relating Wash Frequency and
Hair Condition
There are less rigorous data available to address the
impact of low wash frequency on hair condition. In a
study of the consumer perception of hair quality ex-
pressed as good or bad “hair days,” it was found [15] that
lower wash frequency led to a higher frequency of “bad
hair days.” This was hypothesized to be due to an accu-
mulation of scalp sebum which is subsequently trans-
ferred to the hair leading to a general greasy appearance
characterized by oily shine and hair fiber-fiber adhesion.
In a comparative study of technical and perceived hair
quality between Caucasians and AA [16], it was found
that a much lower wash frequency amongst AA was as-
sociated with greater hair fragility and decreased growth
rates. Similar observations were reported in a study of
Nigerian females [17]. As mentioned above [11], sebor-
rheic dermatitis is also more prevalent in this group,
which has been demonstrated to impact the quality of
hair emerging from the scalp [18]. Scalp sensitivity, which
has been shown to be increased by low wash frequency
and accumulated sebum [14], has been shown to associate
with increased hair loss [19].

Shampoo Wash Frequency
185
Skin Appendage Disord 2021;7:183–193
DOI: 10.1159/000512786
Summary of Relevant Literature
A general interpretation begins to emerge from the
published literature. Low wash frequency allows scalp se-
bum level to increase as well as the proportion of chemi-
cally modified potentially harmful components within
the sebum (such as oxidized free fatty acids). This mate-
rial tends to increase the prevalence of scalp-related is-
sues, which can be manifested in common itch or more
defined etiologies such as seborrheic dermatitis. Either
directly or indirectly (via scalp-impacted hair growth ef-
fects), low wash frequency tends to have detrimental ef-
fects on hair, but much of this comes specifically from
evaluating AA hair and the typical low wash frequency
habit.
The Need for Objective Data
The increasing perception that shampoo has the po-
tential to harm the hair has led to a decrease in wash fre-
quency globally. Paradoxically, this behavior may have
the opposite effect on hair (and scalp). The research re-
ported herein is aimed at generating objective data relat-
ing wash frequency to resultant effects on scalp and hair
condition. We report here two studies aimed at adding
objective data to enable informed decisions of optimum
wash frequency. One is an epidemiological study while
the other is a treatment study, both of which combined
objective technical assessments with self-perception eval-
uations.
Materials and Methods
Epidemiological Study
Study Design
A 2-week epidemiological study was conducted in Xi’an, Chi-
na, with 1,500 healthy male and female subjects of Chinese ethnic-
ity with no known scalp pathologies, aged 18–75 years old after
obtaining the informed consent under the principles of Good Clin-
ical Practice (see Tables 1 and 2 for a summary of population de-
mographics and Fig.1 for a visual summary of hair textures). No
treatments were involved in this epidemiological study. Recruit-
ment resulted in 200–300 subjects in each wash frequency group:
≤1×/week, 2×/week, 3–4×/week, 5–6×/week and 7×/week. This
enabled the evaluation of the impact of wash frequency on scalp
and hair conditions. Figure 1 demonstrates the hair type and tex-
ture of recruited females in the epidemiological study.
Measures
Dandruff flaking severity was quantified using the Adherent
Scalp Flaking Score (ASFS) as described [20]. The baseline visit
included a self-perception assessment questionnaire designed to
capture subject-relevant outcomes (e.g., severity of scalp flaking)
using a categorical scale that varied from “none” to “very severe”
(0 = none, 1 = slight, 2 = slight to moderate, 3 = moderate, 4 =
moderate to severe, 5 = severe, and 6 = very severe). Subjects were
asked to refrain from shampooing and using any hair styling prod-
ucts prior to scheduled visits during which they underwent ASFS
measurement and completed self-assessment questionnaires.
Treatment Study
Study Design
This was a 5-week, double-blind, IRB-approved study conduct-
ed in Xi’an, China, with 60 healthy male and female participants
between the ages of 18–50 with no known scalp pathologies. En-
rolled subjects habitually washed their hair with low frequency (≤2
times per week) and refrained from use of scalp treatments, medi-
cations, hair oils, serums, or anti-dandruff shampoos in the past 4
weeks. The study was conducted under the principles of Good
Clinical Practice (see Table3 for a summary of population demo-
graphics). The study was divided into sequential phases, differing
in the frequency of use of a provided shampoo (a potentiated ZPT
scalp care shampoo [21]). The first phase of the study, lasting one
week, had one initial controlled shampoo application followed by
a refrain of 7 days with no shampoo use. The second phase of the
Table 1. Epidemiological-study wash-frequency population distri-
bution
% wash frequency (male and female)
Age range,
years
7×/
week (daily)
5–6×/
week
3–4×/
week
2×/
week
≤1×/
week
18–30 68 79 20 2 0
31–45 24 15 27 15 7
46–60 7 6 43 55 56
61–75 1 0 10 28 37
Table 2. Epidemiological study wash frequency population hair
length distribution
Hair length Male, % Female, %
Close cut 87 2
Ear length 12 8
Ear length to shoulder length 1 13
Shoulder length 0 12
Greater than shoulder length 0 65
Table 3. Treatment clinical population parameters
Phase 1:
“7-day refrain”
Phase 2:
“daily wash”
Subjects, N60 60
Female, n (%) 56 (93) 56 (93)
Male, n (%) 4 (7) 4 (7)
Age, years, mean (SD) 43.4 (6.2) 43.4 (6.2)

Punyani/Tosti/Hordinsky/Yeomans/
Schwartz
Skin Appendage Disord 2021;7:183–193
186
DOI: 10.1159/000512786
study, lasting 4 weeks, comprised daily wash (controlled applica-
tion) with the same shampoo. Subjects refrained from the use of
any other scalp/hair products throughout the course of the study.
Hair Wash Protocol
Study personnel filled a 10 mL syringe with shampoo and ad-
justed water temperature between 32 and 38°C and flow rate at
5.1–6.3 L/min for hair wash. Subjects leaned over the front of the
shampoo station to wet their scalp completely. The shampoo was
dispensed equally across the subject’s entire head, after which the
subject gently massaged the shampoo into the entire scalp for 45 s.
Subject rinsed shampoo from their hair until water ran clear. Sub-
jects used a blow dryer to dry their hair.
Two assessment time points occurred: at the end of the 7-day
refrain period (“7-day refrain”) and 24 h after the last wash of 4
weeks of daily washing (“daily wash”). The 4-week period of daily
washing enabled enough time for new hair to grow and emerge
from the scalp under the new scalp condition resulting from daily
washing. For analysis of hair samples, the most recently grown seg-
ment (approximately 1 cm) was used.
Measures
Measures included technical measures and self-assessments of
both scalp and hair conditions. Most scalp assessments were made
directly on scalp or on extracts of the scalp surface. Hair samples
were collected from a 2.5 × 2.5 cm square area on both sides of the
scalp. At the end of phase 1, a template was used to mark the hair
collection area and a cosmetologist clipped the hair with scissors
and placed the hair in glassine envelopes, keeping the orientation
of the fiber bundle consistent. The hair collection procedure was
repeated at the end of phase 2 after ∼2 cm of new growth. For hair
analysis, the length of the sample was measured, and the portion
of the sample that was closest to the scalp (representing newest
growth) was utilized. An equal length of hair was cut from the
proximal end of the phase 1 hair sample. The phase 1 and 2 visits
included a self-perception assessment questionnaire designed to
capture subject-relevant outcomes (e.g., severity of scalp flaking)
using a categorical scale that varied from “none” to “very severe.”
Table 4 summarizes the measures, the details of which can be
found in the online suppl. Material (for all online suppl. material,
see www.karger.com/doi/10.1159/000512786).
Fig. 1. Example of hair type and texture of recruited females in the epidemiological study.
Table 4. Summary of measures and methods used for the treatment study
Measure Method Sampling Description
Scalp flaking level Expert grading Direct visual Expert visual grading of scalp surface flakes
Scalp surface lipids FTIR Direct surface probe Spectroscopic identification of sebaceous lipids
Scalp odor Expert grading Direct sniffing Expert olfactory grading
Scalp surface visual Handheld microscope Direct surface probe Magnified scalp surface
Oxidative stress marker MS Scalp tape strip;
Hair direct extraction
Quantitation of oxidized linoleic acid (HODE)
Hair lipids GC Extract of cut hair Separation and quantitation of sebaceous and internal lipids
Hair water absorption DVS Directly on cut hair Gravimetric analysis; controlled humidity and temperature
Hair shine Gloss meter Directly on cut hair Evaluation of specular reflectance
Hair surface visual SEM Directly on cut hair Highly magnified hair surface
FTIR, Fourier-transform infrared spectroscopy; MS, mass spectroscopy; GS, gas chromatography; DVS, dynamic vapor sorption; SEM, scanning electron
microscopy.

Shampoo Wash Frequency
187
Skin Appendage Disord 2021;7:183–193
DOI: 10.1159/000512786
Statistical Analysis
After completion of the epidemiological and treatment study,
data were checked for accuracy and completeness. All subjects
were evaluated for compliance with study protocol at each visit,
and their evaluability was determined prior to database locking.
Statistical analyses were performed on evaluable data. Logarithm
transformation was applied to biomarker data prior to analysis to
stabilize the variance. A statistical test was determined to be sig-
nificant if a two-sided p value <0.05.
Results
Scalp Technical Results (Epidemiological Study)
Scalp flaking severity, as determined by the ASFS
method, decreased significantly with increase in wash fre-
quency (Fig.2). These data represent the results of the
total panel and are independent of either age or gender
(online suppl. Table 1).
Scalp Condition Self-Perception Results
(Epidemiological Study)
Self-perception assessment questionnaires completed
for different wash frequencies revealed statistically sig-
nificant reduction in the severity of self-perceived scalp
dandruff, itch, and dryness with increases in wash fre-
quency (Fig.3). The reduction in scalp dandruff percep-
tion coincided with the improvements observed in tech-
nical dandruff severity based on the ASFS grading meth-
od. These data represent the results of the total panel and
are independent of either age or gender. Please refer on-
line suppl. Table 2 for total (male and female) and gender-
wise data.
Hair Condition Self-Perception Results
(Epidemiological Study)
Hair condition self-perception assessment revealed no
discernible negative outcomes as a result of increased
wash frequency. Specific parameters summarized in Fig-
ure 4 are hair loss, hair brittleness (both of which slightly
improved at high wash frequency), and hair smoothness.
Please refer online suppl. Table 3 for total (male and fe-
male) and gender-wise data.
A comprehensive parameter that reflects self-percep-
tion of hair condition was evaluated and termed “great
hair days,” representing the overall satisfaction of the
panelist with their hair look and feel. Using this metric,
the number of days per week a panelist has overall satis-
faction with their hair condition increases significantly
14
12
10
Scalp Flaking Score
8
6
4
2
0
≤1× 2× 3–4×
Wash Frequency per week
5–6× Daily
aa
b
c
d
Mean
Fig. 2. Scalp Flaking Score graded by experts as function of wash
frequency in epidemiological study. The mean ASFS is plotted
with standard error bars. Results not connected by same letter are
significantly different. ASFS, Adherent Scalp Flaking Score.
2.0
1.5
Scalp Issue Severity Perception
1.0
0.5
0
≤1× 2× 3–4× 5–6×
Wash Frequency (times per week)
Daily
a
a
a
a
a
aa
a
a
b
b
b
b
b
c
Dandruff
Itch
Dry
Fig. 3. Self-perceived scalp parameters dandruff, itch, and dryness
of n = 1,500 males and females as function of wash frequency in the
epidemiological study. The mean is plotted with standard error bars.
Results not connected by same letter are significantly different.

Punyani/Tosti/Hordinsky/Yeomans/
Schwartz
Skin Appendage Disord 2021;7:183–193
188
DOI: 10.1159/000512786
the more frequently they wash their hair (Fig.5). These
results were independent of age and gender. Please refer
online suppl. Table 4 for total (male and female) and gen-
der-wise data.
Scalp Condition Technical Results (Treatment Study)
Compared with the 7-day refrain period, daily wash
with a potentiated ZPT shampoo resulted in the expected
significantly lower amounts of overall scalp surface lipid
1
0.8
0.6
LS means ± SE
0.4
p = 0.0536
0.9859
0.9273
Normalized CH-stretch
(PA)
7-day
refrain
Daily wash 7-day
refrain
Daily wash 7-day
refrain
Daily wash 7-day
refrain
Daily wash
LS means ±SE
p < 0.0001
HODE-9
(absolute amount)
1.5
1
0.5
0
1.36
0.54
LS means ± SE
p < 0.0001
ASFS
14
12
10
8
6
4
12.97
4.90
LS means ± SE
p < 0.0001
32
30
28
26
24
22
Odor
29.50
21.50
a b cd
Fig. 6. Technical scalp measurements for total sebum lipids (normalized CH-stretch PA) (a), oxidized lipids
(HODE-9) (b), flaking score (ASFS) (c), and odor intensity at 7-day refrain (yellow bar) and daily wash (blue bar)
(d). For each measurement, lower value indicates healthier scalp. ASFS, Adherent Scalp Flaking Score.
7
6
5
4
Number of Great Hair Days Per Week (Mean)
3
2
1
≤1× 2× 3
–
4× 5
–
6×
Wash Frequency (times per week)
Daily
Mean
aa
b
c
d
Fig. 5. Self-perceived of number of “great hair days” improved for
n = 1,500 males and females as function of wash frequency. The
mean is plotted with standard error bars. Results not connected by
the same letter are significantly different.
2.0
1.5
Hair issue severity perception
1.0
0.5
0
≤1× 2× 3–4× 5–6× Daily
Wash frequency per week
a
a
a
a, b a, b
a
a
b
b
b
b, c
a
a
aa
Hair loss
Hair brittle
Hair not smooth
Fig. 4. Self-perceived hair attributes hair loss, hair brittleness, and
hair not smooth of n = 1,500 males and females as function of wash
frequency in the epidemiological study. The mean is plotted with
standard error bars. Results not connected by the same letter are
significantly different.

Shampoo Wash Frequency
189
Skin Appendage Disord 2021;7:183–193
DOI: 10.1159/000512786
and fatty acid of sebum as measured on scalp (Fig.6a).
The level of a scalp health biomarker of oxidized lipid
(HODE) is also significantly reduced with daily wash ver-
sus 7-day refrain (Fig.6b). Even though the subjects were
not dandruff sufferers with high incoming flaking levels,
daily wash lowered the level of flaking on scalp as mea-
sured by ASFS (Fig.6c). Expert assessment of scalp odor
was also improved by the daily wash regimen relative to
the 7-day refrain (Fig.6d).
Images of the scalp were captured to visually sum-
marize the oil accumulation representative of the low
wash protocol and the improvement because of daily
wash. Representative sample images are summarized in
Figure 7.
Hair Condition Technical Results (Treatment Study)
The daily wash protocol resulted in significantly less
sebum on hair than the 7-day refrain as expected (Fig.8a).
7-day
refrain
Daily
wash
Fig. 7. Selected scalp images comparing the
oil accumulation representative of the
7-day refrain and daily wash protocols.
20,000
15,000
10,000
5,000
0
LS means ± SE
7-day
refrain
Daily wash 7-day
refrain
Daily wash 7-day
refrain
Daily wash 7-day
refrain
Daily wash
p < 0.0001
15,881.2
4,125.3
Total sebum, μg/g
LS means ± SE
1.2
1
0.8
0.6
0.4
p < 0.0001
1.135
0.733
HODE-9 (normalized
by hair weight)
LS means ± SE
2
1.5
1
0.5
0
p < 0.0001
1.52
0.83
Greasy shine,
degree = 60
LS means ± SE
26
25.5
25
24.5
24
p < 0.0001
25.28
24.27
DVS–water uptake
at 90% RH
a
b c d
Fig. 8. Technical hair measurements for total sebum lipids (a), oxidized lipids (HODE) (b), greasy shine (c), and
% water uptake at 7-days refrain (yellow bar) and daily wash (blue bar) (d). For measurements in (a, b, d), lower
value indicates healthier hair. For measurement in (c), lower value indicates a less greasy shine on hair.

Punyani/Tosti/Hordinsky/Yeomans/
Schwartz
Skin Appendage Disord 2021;7:183–193
190
DOI: 10.1159/000512786
Evaluation of the proportion of sebum that has been oxi-
dized (using the established biomarker HODE), it was ob-
served that daily wash resulted in significantly less oxida-
tion (Fig.8b), both paralleling the scalp results. Measure-
ment of greasy hair shine demonstrated daily wash left
the hair with a less oily (specular) shine (Fig.8c). Finally,
use of DVS to probe hair cuticular surface integrity and
daily wash resulted in lower hair water vapor absorption
indicating a more effective cuticular barrier (Fig.8d).
Images of the hair were captured to visually summa-
rize the oil accumulation representative of the low wash
protocol and the improvement because of daily wash.
Representative sample images are summarized in Fig-
ure 9.
Internal hair lipids were quantified using GC method
to determine whether the two wash protocols affected the
amount of beneficial internal hair lipids. There were no
significant differences observed between the 7-day re-
30,000
25,000
Total Internal Lipids (μg/g of hair)
20,000
15,000
10,000
5,000
0
Internal Fatty
Acids
Internal
Cholesterol
Internal Wax
Esters
Internal
Triglycerides
Total Internal
Hair Lipids
aaaaa
a
a
a
■ 7-Day Refrain
■ Daily Wash
aa
Fig. 10. Quantification of internal hair lipids using GC method as a result of 7-day refrain and daily wash proto-
cols. No significant differences were observed.
7-day refrain
Daily wash
BMI 346 1.0 kV 10.5 mm × 500 SE(UL) 11/28/2018
BMI 346 1.0 kV 10.6 mm × 500 SE(UL) 11/28/2018
BMI 346 1.0 kV 10.5 mm × 1.00k SE(UL) 11/28/2018
BMI 346 1.0 kV 10.5 mm × 1.00k SE(UL) 11/12/2018
100 μm
100 μm
50.0 μm
50.0 μm
Fig. 9. Selected hair images comparing the
oil accumulation representative of the
7-day refrain and daily wash protocols.

Shampoo Wash Frequency
191
Skin Appendage Disord 2021;7:183–193
DOI: 10.1159/000512786
frain and daily wash protocols in any of the classes of in-
ternal hair lipids (Fig.10).
Self-Perception Evaluation (Treatment Study)
Validating the objective technical assessments, self-as-
sessments indicate whether subjects noticed the impact of
these technical measures on scalp and hair properties. All
attributes evaluated had dramatic improvements upon
transition from the 7-day refrain to the daily wash proto-
col (in some cases, over half of the full rating scale). While
the reduction in oil buildup on both hair and scalp are
likely obvious, the interpretations of the implications are
less obvious: improved perception of hair health and at-
tributes related to it and reduced scalp irritation and itch.
The results are summarized in Figure 11.
Discussion
The question “How frequently should scalp and hair
be washed?” has been difficult to answer definitively due
to lack of relevant objective technical information. There
are concerns among both professionals as well as con-
sumers that washing with surfactant-based products has
the potential to harm either or both the hair and scalp. We
sought to generate data, both technical and panelist self-
assessed, to understand the impact of wash frequency on
the resultant conditions of both hair and scalp. Two dif-
ferent study designs were conducted to address this ques-
tion. In one study (the Epidemiological Study), wash fre-
quency varied based on the normal habits and practices
of a recruited population. A second study (the Treatment
Study) was conducted in a population of low-frequency
shampooers, who were switched to a higher frequency of
shampooing for 1 month. These studies substantially and
uniquely add to the existing literature to enable informed
decision-making regarding optimum wash frequency for
hair and scalp care.
Impact of Wash Frequency on Scalp Condition
In the Epidemiological Study, those washing with a
higher frequency experienced less flaking as judged both
by experts as well as self-perceived less flaking, itch, and
dryness. In the Treatment Study, switching from low to
high wash frequency resulted in significant decreases in
the technical parameters of scalp sebum level, degree of
flaking, amount of oxidized sebaceous lipids, and scalp
odor. These were accompanied by corresponding self-
perceived improvements in these same attributes as well
as more composite parameters (such as irritation).
The data from these two studies are entirely consistent
with the studies existing already [10–12] supporting the
observation that increased wash frequency results in de-
creased scalp flaking and itching. These studies, however,
extend the beneficial scalp impacts to considerably more
technical and self-assessment measures. For example,
new measures of decreased oxidative stress (using the
biomarker HODE) may add to the mechanistic explana-
tions as to why sebum accumulation on the scalp is gen-
erally detrimental to its condition. This work also extends
6
5
4
3
2
1
0
–1
–2
–3
–4
–5
–6
Better during refrain Better during wash
Delta improvement
Oily
Unhealthy
Frizzy
Dull
Dry
Breakage
Oily
Odor
Itch
Buildup
Flakes
Dryness
Irritation
Scalp attributesHair attributes
a b
Fig. 11. Improvement of self-perception of hair (a) and scalp (b) attributes upon switching from 7-day refrain
versus daily wash protocol. A categorical scale 0–10 was used for the worst of the conditions panelists had during
the last 24 h, where 0 = none and 10 = worst imaginable. p values are based on pairwise t test.

Punyani/Tosti/Hordinsky/Yeomans/
Schwartz
Skin Appendage Disord 2021;7:183–193
192
DOI: 10.1159/000512786
the symptomatic observations to include malodor gen-
eration. Taken together, there is a strong group of data
that consistently supports the understanding that low
wash frequency allows sebum to accumulate, become
progressively chemically modified and irritating leading
to increased prevalence of resultant symptoms (flakes,
itch, and dryness). A significant aspect of the irritation
likely originates from the formation and accumulation of
species such as oxidized lipids that lead to oxidative stress
[22]. These observations are consistent in both technical
measures and individual self-assessments. As a whole, the
data support that increased scalp washing is beneficial for
both normal scalps as well as those exhibiting pathologies
such as seborrheic dermatitis.
Impact of Wash Frequency on Hair Condition
While the conclusions regarding the detrimental impact
of low wash frequency on scalp condition are widely ac-
cepted, the impact on hair condition is considerably more
controversial, largely due to the paucity of existing data. In
the Epidemiological Study, the panelists observed no nega-
tives to hair condition with increased wash frequency and
the trend was always in the direction that increased wash
frequency decreased hair issues. Smooth feel perception
did not statistically significantly improve, but both hair loss
perception and brittleness perception did significantly im-
prove with increasing wash frequency. These attributes,
and likely many more, can be combined into a global col-
loquial term “great hair days.” [15] Using this global metric,
increasing wash frequency resulted in dramatic improve-
ment of overall hair satisfaction: 2 or less washes per week
resulted in less than 3 great hair days per week whereas
daily washing led to over 5 great hair days per week.
In the Treatment Study, objective technical parameter
measurement provides important insights to definitively
address the impact of wash frequency on hair condition.
Reduction of sebum level and greasy shine are to be ex-
pected. As with the scalp, a reduction in oxidative stress
has been observed with increased wash frequency. The
relationship between the oxidative stress status of the
scalp and resultant oxidative stress of the hair has been
previously established [18] and has been confirmed here,
with wash frequency being the driver of improved condi-
tions of both. Continuing the parallel, the hair obtained
from those with higher wash frequency was in better con-
dition in that the protective cuticular barrier was more
functionally effective, enabling reduced water vapor ab-
sorption. Again, this has previously been observed as a
result of reduced oxidative stress to scalp and resultant
hair produced from it [23].
An important measure of impact of treatments on hair
condition is the impact on internal lipids that build the
cuticular structure. Harsh treatments are known to cause
the reduction of these beneficial lipids [24]. Removal of
these beneficial lipids has been shown to cause greater
roughness, permeability, and reduced structural integrity
[25]. Shampoo products can be formulated to inhibit any
such effects [26]. In the treatment study, daily wash for 28
days with a well-formulated, mild scalp care shampoo
showed that no significant loss in internal lipids occurred
as a result of increased wash frequency. The subjects in
this study self-assessed their condition as dramatically
better at the higher wash frequency: reduced oiliness,
more healthy, less frizz, less dull, less dry, and reduced
breakage.
Taken together, the data from these two studies strong-
ly support the conclusion that increased wash frequency
is beneficial to self-perceived hair condition and not det-
rimental to technically assessed hair quality for the Asian
population studied. One of the primary technical con-
cerns reported with excessive washing has been loss of
internal beneficial lipids; this was not observed in this
work. Both of these studies consisted of Asian individuals
with straight or low-texture hair (visually exemplified in
Fig.1). It is not known whether the results observed here
are generalizable to hair types with much higher texture/
curl. However, preliminary data from an epidemiological
study involving Nigerian women demonstrated higher
wash frequency was associated with less hair complaints
[27]. It is also possible that greater use of styling imple-
ments than used in these studies could contribute to hair
damage separate from washing itself.
Summary
These two studies significantly increase the rigorous
objective data available to assess the impact of shampoo
wash frequency on scalp and hair conditions. There is
little doubt that increased wash frequency is beneficial to
scalp condition. However, the data also strongly support
that for the Asian populations studied, hair condition is
not negatively affected by increased wash frequency and
that the self-perception is toward marked improvement.
The overall model of detrimental effects of sebum, espe-
cially oxidized versions, is consistent with other observa-
tions relating scalp to hair health. Thus, these data should
serve as an important asset to offset the unfounded con-
cerns that high shampoo wash frequency is detrimental
in any way.

Shampoo Wash Frequency
193
Skin Appendage Disord 2021;7:183–193
DOI: 10.1159/000512786
Acknowledgements
We acknowledge A. Yu for clinical trial management. The fol-
lowing individuals made various analytical measures: S. Whitaker,
H. Kang, L. Li, A. Ritter and H. Lau. Statistics were performed by
X. Ying and L. Xu.
Statement of Ethics
Studies were conducted in concordance with the World Medi-
cal Association Declaration of Helsinki. All subjects provided in-
formed, written consent. The treatment study was reviewed and
approved by Beijing Health Tech Research Co., Ltd. as study CSD
2018037.
Conflict of Interest Statement
S.P. and J.S. are employees of the Procter & Gamble Company,
which paid 100% of the costs of this work.
Funding Sources
These studies were funded by the Procter & Gamble Company.
Author Contributions
All authors contributed equally to study design, data interpre-
tation, and drafting the manuscript.
References
1 Tuminoct R. How often should you really
wash your hair? New York Times. 2016 Oct
26.
2 Shapiro B. Are you not washing your hair
enough? New York Times. 2017 Jan.
3 Morley K. Women are washing their hair less
than three times a week for the first time in a
decade. The Telegraph. 2017 Feb 15.
4 Kent E. Shampoo sales fall by £23million over
the past year because women who work at
home don’t bother to wash their hair. Daily
Mail. 2016 Dec 19.
5 Grice EA, Segre JA. The skin microbiome. Nat
Rev Microbiol. 2011; 9(4): 244–53.
6 DeAngelis YM, Gemmer CM, Kaczvinsky JR,
Kenneally DC, Schwartz JR, Dawson TL Jr.
Three etiologic facets of dandruff and sebor-
rheic dermatitis: Malassezia fungi, sebaceous
lipids, and individual sensitivity. J Investig
Dermatol Symp Proc. 2005; 10(3): 295–7.
7 Chiba K, Kawakami K, Sone T, Onoue M.
Characteristics of skin wrinkling and dermal
changes induced by repeated application of
squalene monohydroperoxide to hairless
mouse skin. Skin Pharmacol Appl Skin Physi-
ol. 2003; 16(4): 242–51.
8 Sugita T, Yamazaki T, Yamada S, Takeoka H,
Cho O, Tanaka T, et al. Temporal changes in
the skin Malassezia microbiota of members of
the Japanese Antarctic Research Expedition
(JARE): a case study in antarctica as a pseudo-
speace environment. Med Mycol. 2015; 53:
717–24.
9 Sugita T, Yamazaki T, Makimura K, Cho O,
Yamada S, Ohshima H, et al. Comprehensive
analysis of the skin fungal microbiota of astro-
nauts during a half-year stay at the interna-
tional space station. Med Mycol. 2016; 54(3):
232–9.
10 Schwartz J, Cardin C, Dawson T Jr. Dandruff
and seborrheic dermatitis. 3rd ed. In: Baran R,
Maibach H, editors. Textbook of cosmetic
dermatology. New York: Taylor & Francis;
2005. p. 259–72.
11 Roseborough IE, McMichael AJ. Hair care
practices in African-American patients. Se-
min Cutan Med Surg. 2009; 28(2): 103–8.
12 Kobayashi M, Ito K, Sugita T, Murakami Y,
Yamashita R, Matsunaka H, et al. Physiologi-
cal and microbiological verification of the
benefit of hair washing in patients with skin
conditions of the scalp. J Cosmet Dermatol.
2016; 15(4): e1.
13 Kato K. Studies on sebum on scalp and sham-
poo: time-lapse changes in the amounts of tri-
glyceride and free fatty acid on the scalp and
subjective symptoms for one week. Sanarwa
ta Kwalejin Fasaha ta Jami’a ta Hokkaido.
1997; 10: 47–58.
14 Ma L, Guichard A, Cheng Y, Li J, Qin O,
Wang X, et al. Sensitive scalp is associated
with excessive sebum and perturbed microbi-
ome. J Cosmet Dermatol. 2019; 18(3): 922–8.
15 Birch MP, Messenger A. ‘Bad hair days’, scalp
sebum excretion and the menstrual cycle. J
Cosmet Dermatol. 2003; 2(3–4): 190–4.
16 Lewallen R, Francis S, Fisher B, Richards J, Li
J, Dawson T, et al. Hair care practices and
structural evaluation of scalp and hair shaft
parameters in African American and Cauca-
sian women. J Cosmet Dermatol. 2015; 14(3):
216–23.
17 Ayanlowo O, Otrofanowei E. Hair care prac-
tices, scalp disorders and psychological effects
on women in Nigeria. Washington, DC: An-
nual Meeting of the American Academy of
Dermatology; 2019.
18 Schwartz JR, Henry JP, Kerr KM, Flagler MJ,
Page SH, Redman-Furey N. Incubatory envi-
ronment of the scalp impacts pre-emergent
hair to affect post-emergent hair cuticle integ-
rity. J Cosmet Dermatol. 2018; 17(1): 105–11.
19 Misery L, Rahhali N, Ambonati M, Black D,
Saint-Martory C, Schmitt AM, et al. Evalua-
tion of sensitive scalp severity and symptom-
atology by using a new score. J Eur Acad Der-
matol Venereol. 2011; 25(11): 1295–8.
20 Bacon RA, Mizoguchi H, Schwartz JR. Assess-
ing therapeutic effectiveness of scalp treat-
ments for dandruff and seborrheic dermatitis,
part 1: a reliable and relevant method based
on the adherent scalp flaking score (ASFS). J
Dermatolog Treat. 2014; 25(3): 232–6.
21 Schwartz JR, Bacon RA, Shah R, Mizoguchi
H, Tosti A. Therapeutic efficacy of anti-dan-
druff shampoos: a randomized clinical trial
comparing products based on potentiated
zinc pyrithione and zinc pyrithione/climba-
zole. Int J Cosmet Sci. 2013; 35(4): 381–7.
22 Trüeb RM, Henry JP, Davis MG, Schwartz JR.
Scalp condition impacts hair growth and re-
tention via oxidative stress. Int J Trichology.
2018; 10(6): 262–70.
23 Schwartz JR, Henry JP, Kerr KM, Mizoguchi
H, Li L. The role of oxidative damage in poor
scalp health: ramifications to causality and as-
sociated hair growth. Int J Cosmet Sci. 2015;
37(Suppl 2): 9–15.
24 Masukawa Y, Tsujimura H, Tanamachi H,
Narita H, Imokawa G. Damage to human hair
caused by repeated bleaching combined with
daily weathering during daily life activities.
Exog Dermatol. 2004; 3(6): 273–81.
25 McMullen RL, Laura D, Chen S, Koelmel D,
Zhang G, Gillece T. Determination of physi-
cochemical properties of delipidized hair. J
Cosmet Sci. 2013; 64(5): 355–70.
26 Marsh JM, Brown MA, Felts TJ, Hutton HD,
Vatter ML, Whitaker S, et al. Gel network
shampoo formulation and hair health bene-
fits. Int J Cosmet Sci. 2017; 39(5): 543–9.
27 Ayanlowo O, Otrofanowei E. Hair care prac-
tices, scal disorders and psychological effects
on women in Nigeria. Washington DC: An-
nual Meeting of The American Academy of
Dermatology; 2019.