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Application Patterns Among Participants Randomized to Daily Sunscreen Use in a Skin Cancer Prevention Trial
Rachel Neale, PhD;
Gail Williams, PhD;
Adèle Green, MB BS, PhD
Arch Dermatol. 2002;138:1319-1325.
ABSTRACT
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Background Despite many investigations of sunscreen use, there have been few among
adults in the community at large. Better understanding of sunscreen application
patterns will lead to more strategic skin cancer prevention strategies among
sun-exposed populations.
Objective To explore patterns of sunscreen use, particularly the quantity of sunscreen
used and the application frequency, among participants in a community-based
sunscreen intervention.
Design Follow-up of patterns of sunscreen use over 4.5 years.
Setting Nambour, a subtropical town in Queensland, Australia.
Participants People drawn randomly from the electoral register who were later randomized
as part of a skin cancer prevention trial.
Interventions Daily application of a standard sun protection factor 15+ broad-spectrum
retail sunscreen to the head and neck, arms, and hands.
Outcome Measures Frequency of application of sunscreen, weight of sunscreen applied,
and quantity applied per unit area of skin.
Results Fifty-six percent of participants reported applying sunscreen on at
least 5 days per week, with 27% using sunscreen infrequently on 2 or fewer
days per week. The median daily amount of sunscreen applied averaged over
the duration of the trial was 1.5 g/d (range, 0-7.4 g/d). The median quantity
of sunscreen applied was 0.79 mg/cm2, which was less than half
the amount needed to achieve the labeled sun protection factor.
Conclusions It is possible to implement the daily application of sunscreen in sun-exposed
populations, although protection would be increased if the quantity of sunscreen
applied were greater.
INTRODUCTION
KERATINOCYTE SKIN cancers are the most commonly occurring cancers in
white populations and represent a potentially serious health burden in sun-exposed
populations1-2 in terms of morbidity,
cosmetic disfigurement, and costs to the health care system. For example,
of the 10 most expensive cancers in Australia, keratinocye cancers are the
most costly, accounting for approximately Austral $232.2 million per year.3 Primary prevention in susceptible people therefore
remains a challenge.
It is now generally accepted that the main cause of keratinocyte cancers
is exposure to solar UV radiation,4 and it
is likely that sun exposure during adulthood may contribute to the progression
of keratinocytic cells down the pathway to neoplasia. Reducing exposure of
adult skin to solar UV radiation is thus a primary aim of public education
strategies, with promotion of sunscreen use as a key supplementary measure
to sun avoidance.5
Most public health campaigns widely promote the use of sunscreen on
an ad hoc basis when specific activities in the sun are planned, yet many
people are still not consistently using sunscreen as an adjunct measure for
sun protection. In Victoria, Australia, where the impact of a skin cancer
prevention campaign has been comprehensively evaluated, the number of questionnaire
respondents reporting that they almost always or usually used maximum protection
sunscreen "when outside in the sun" did not increase between 1991 and 1997,
but remained constant at approximately 45%.6 When
a sample from the same population was asked to specify their sunscreen use
when outdoors the previous day,7 the proportion
of sunscreen users was lower, suggesting that, when asked to generalize their
sun protection behavior, people failed to consider sun exposure occurring
during routine daily activities. It is likely that in sunny places, such as
Australia and much of the United States and Europe in summer, a high proportion
of ultraviolet exposure is accumulated "incidentally" during routine outdoor
activities rather than as a result of intentional exposure. Strategies to
reduce such incidental exposures may represent a promising future for skin
cancer control.
This was the rationale underpinning the design of the Nambour Skin Cancer
Prevention Trial, which demonstrated the effectiveness of an intervention
specifying the daily application of sunscreen to exposed body sites for the
reduction of squamous cell carcinoma tumors.5 We
have reported previously that the effectiveness of this community-based intervention
did not appear to be due to measurable changes in sun protection behaviors
apart from sunscreen application and was most likely attributable to changes
in patterns of sunscreen use.8 The aim of the
study reported herein was to further explore the implementation patterns of
the intervention group, particularly the weight of sunscreen used, the application
frequency, and the amount of sunscreen applied per unit of skin surface area
(hereafter referred to as quantity), among the people
randomized to sunscreen use. Better understanding of the sunscreen application
patterns among the intervention group in this successfully implemented trial
will help inform future public health skin cancer prevention strategies among
similarly exposed populations.
METHODS
The conduct of the Nambour Trial was approved by the Queensland Institute
of Medical Research Ethics Committee, and written informed consent was obtained
from all participants. The design and methods have been described in detail
previously.9 Briefly, the Nambour Trial was
a 2 x 2 factorial field trial to test the interventions of daily sunscreen
application and beta carotene supplementation for the prevention of skin cancer
over 5 years. Participants were residents of Nambour (a subtropical town of
around 8000 people lying 100 km north of Queensland's capital, Brisbane, Australia).
In 1992, 1621 residents randomly selected from those who had participated
in a previous skin cancer survey were randomly assigned to 1 of 4 groups (beta
carotene tablets and sunscreen, placebo tablets and sunscreen, beta carotene
only, or placebo only). The original skin cancer survey participants had been
randomly selected from the electoral roll (enrollment is compulsory). The
mean age of participants in the present trial was 49 years, and 44% were male.
Nineteen percent had worked in mainly outdoor occupations, and approximately
27% reported having had a previous skin cancer.
The sunscreen intervention required daily application of a supplied
standard sun protection factor 15+ sunscreen to the face, rest of the head
and neck, hands, and arms. The sunscreen was a water-resistant, oil-in-water,
cream formulation containing octyl methoxycinnamate, oxybenzone, and butyl
methoxydibenzoylmethane. It was supplied in standard 250-mL bottles with a
flip-open cap covering an opening of approximately 5 mm. Participants were
instructed to apply sunscreen every day, regardless of planned activities
or weather conditions. The weight or quantity of sunscreen to be applied at
each application was not specified beyond "adequate." The weight of sunscreen
used by each participant in the sunscreen intervention group was calculated,
in addition to the self-reported frequency of application.
MEASUREMENT OF THE WEIGHT OF SUNSCREEN USED
Every 3 to 4 months during the 5 years of the trial, beginning in February
1992 and ending in August 1996, participants were required to attend designated
"distribution" weekends at a central location, when used sunscreen bottles
were collected and new bottles supplied as required. Research assistants,
using carefully standardized scales, weighed returned bottles. Any participants
who failed to attend distribution weekends were contacted, provided with a
fresh bottle, and asked to estimate the proportion of sunscreen remaining
in each bottle (the used bottle was to be weighed later, when possible). Some
used bottles were not subsequently weighed, and in such cases the estimated
proportions remaining were converted to weights of sunscreen and marked as
proxy measurements. A total of 1621 participants were initially enrolled in
the trial, 812 of whom were in the sunscreen intervention group.5 Information
regarding the weight of sunscreen used was available for at least one distribution
period for 764 participants in the intervention group (94%).
To calculate the average weight of sunscreen used per day for the intervals
between sunscreen distributions, the weight of sunscreen remaining in the
bottle was subtracted from the total weight of sunscreen supplied, and the
difference was divided by the number of days in the interval between supply
and return. Because the dates of contact with each participant were not the
same, the average daily rates of use were calculated for 18 standard 3-month
periods, corresponding to seasons, to enable analysis of changes in the weight
of sunscreen used by season and over time. The average daily sunscreen used
over the entire trial period was calculated as the total weight of sunscreen
supplied minus the total returned, divided by the total number of days over
which this sunscreen was used.
QUESTIONNAIRE-BASED ASSESSMENT OF FREQUENCY OF SUNSCREEN USE
A questionnaire that asked a broad range of questions regarding attitudes
toward sun protection and sun-protective behaviors was self-administered in
the final year of the trial. With regard to sunscreen, participants specifically
reported their usual frequency of sunscreen application (days per week and
times per day) separately for the face, rest of the head and neck, hands and
arms, and other body sites.
STATISTICAL METHODS
Statistical analysis was mainly performed with SAS software.10 Measurements calculated and compared were the frequency
and weight of sunscreen used during the course of the trial. The analysis
was predominantly descriptive; weighted  (using default SAS weights)
was used to estimate the differences in sunscreen application frequency to
different body sites. To assess associations between personal characteristics
and the weekly frequency of sunscreen use, we calculated adjusted prevalence
ratios (PRs) by using Poisson regression. Possible predictors were divided
into groups relating to exposure, complexion, and sun-related skin damage
(eg, nuchal elastosis: degeneration of the dermal elastic tissue of the neck,
clinically assessed by dermatologists). Variables with the largest effect
size within each group were selected first, and the remaining variables were
then assessed for their contribution to the fit of the model.
The body surface area of participants was calculated from the following
formula: (heightxweight)/3600.11 If height
or weight was missing, the sex-specific mean was assigned for the calculation
of body surface area. The exposed parts of the head and the neck together
were considered to constitute 4%, and the hands and arms, 8.5%, of the total
body surface area.12 The quantity of sunscreen
applied was estimated by first calculating the body surface area in square
centimeters to which sunscreen was applied in a typical week, based on the
number of days and times per day sunscreen was recorded in the questionnaire
as being applied to the required sites. The total sunscreen applied in a typical
week was then divided by the estimated surface area of application.
To assess associations with the average quantity of sunscreen used,
the 18 people who did not use sunscreen were excluded and the distribution
among users was normalized by a logarithmic transformation. Multivariate linear
modeling was used to determine independent associations with sunscreen quantity.
The coefficients from the final model were exponentiated to calculate the
ratio of the quantity of sunscreen used in the relevant category relative
to the reference category.
RESULTS
WEIGHT OF SUNSCREEN USED
Among the 764 participants in the sunscreen intervention group for whom
sunscreen usage during the course of the trial was available, the median daily
weight of sunscreen applied on average during the duration of the trial was
1.5 g/d (range, 0-7.4 g/d). The rate of sunscreen application varied across
the 18 distribution periods of the trial according to season, with generally
less sunscreen being used in the 3 winter months than in the 3 summer months.
Median sunscreen use in winter was 1.39 g/d (interquartile range, 0.84-1.99
g/d), and in summer, 1.59 g/d (interquartile range, 1.01-2.36 g/d) (P<.001 for winter vs summer difference). In addition,
sunscreen use decreased as the trial progressed; the median daily weight of
sunscreen application each year from 1992 to 1996 was 1.67, 1.61, 1.46, 1.41,
and 1.22 g, respectively.
FREQUENCY OF SUNSCREEN USE
Questionnaires were sent to 1329 participants, including 96 participants
who had withdrawn but were able to be located. Seven hundred thirty-four participants
in the sunscreen intervention group received the questionnaire, 659 (90%)
of whom completed the questions regarding the frequency of sunscreen use.
Most reported applying sunscreen to the face, arms, and hands the same number
of days per week (weighted = 0.85). Applications to the face have
therefore been used as indicative of the frequency of sunscreen application
to the sites specified by the intervention regimen. A total of 356 participants
(56%) who completed the relevant question reported applying sunscreen to the
face at least 5 days per week, while 27% used sunscreen infrequently at 2
or fewer days per week (Table 1).
Sunscreen application to other sites not specified in the study protocol was
less frequent, with almost half of participants reporting no regular application.
Women (P = .04) and participants older than 60 years
(P<.001) were more likely to report application
to these sites than men and those younger than 60 years. These results are
in stark contrast to the control group, 74% of whom applied sunscreen to the
specified sites and 92% to unspecified sites on 2 or fewer days per week.5 Most people who regularly applied sunscreen in both
the intervention and control groups applied it only once per day (Table 2).
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Table 1. Frequency of Sunscreen Application
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Table 2. Frequency of Sunscreen Application
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There was a strong association between the self-reported frequency with
which sunscreen was applied to the face or hands and the weight of sunscreen
used during the distribution period during which the questionnaire was completed
(Spearman rank  = 0.52, P<.001). Nevertheless,
within each of the self-reported categories there was a considerable range
in the weight of sunscreen used per day (Table 3), and this was not altered when the analysis was stratified
by the number of applications per day or applications to other parts of the
body. We therefore considered that it reflected true variation in the thickness
of sunscreen application.
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Table 3. Association Between Self-reported Frequency of Application
and Weight of Sunscreen Used
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QUANTITY OF APPLIED SUNSCREEN
For the 595 participants for whom this information was available, the
quantity of sunscreen applied ranged from 0 mg/cm2 (indicating
that no sunscreen was used) to 6.3 mg/cm2, with a mean of 0.99
mg/cm2 (95% confidence interval [CI], 0.92-1.06 mg/cm2)
and median of 0.79 mg/cm2 (interquartile range, 0.46-1.22 mg/cm2). Excluding the 7 people who did not use sunscreen did not materially
alter these estimates. A total of 324 participants reportedly applied sunscreen
to sites other than the face and hands at least once per day, possibly resulting
in an overestimation of the amount of sunscreen applied to the required sites.
Excluding these people from the analysis resulted in a mean of 1.03 mg/cm2 (95% CI, 0.92-1.14 mg/cm2) and median of 0.79 mg/cm2 (interquartile range, 0.46-1.25 mg/cm2).
ASSOCIATIONS WITH SUNSCREEN USE
Given the relatively high adherence with the requested regimen of daily
sunscreen application, we explored the predictors of nonadherence, ie, using
sunscreen on 2 or fewer days per week. In a model containing age, sex, time
outside, and skin cancer diagnosed during the trial, the strongest predictor
of sunscreen use frequency was the usual amount of time spent outside. People
who reported being outside 4 or more hours per day were two thirds less likely
to be nonadherent than those who spent less than an hour per day outside (PR,
0.33; 95% CI, 0.20-0.59), with those spending between 1 and 4 hours per day
outside being approximately half as likely to be poor adherers (PR, 0.57;
95% CI, 0.41-0.80). Men were approximately twice as likely as women to be
nonadherent (PR, 1.77; 95% CI, 1.29-2.44), but age was not associated with
the weekly frequency of use (P = .69). Diagnosis
of a skin cancer before the trial and during the trial were highly correlated
and were added separately to the model containing sex, age, and time outside.
In both cases, those who had been diagnosed as having skin cancer were approximately
50% less likely than others to be low sunscreen users (skin cancer during
trial PR, 0.48; 95% CI, 0.29-0.80). People with high levels of actinic skin
damage such as a high degree of facial telangiectasia and the presence of
more than 10 solar keratoses on the skin also used sunscreen more frequently
than those with less solar-damaged skin. Skin type, assessed by skin color
(P = .99), tanning ability (P =
.77), and hair (P = .65) or eye (P = .90) color were not associated with the weekly frequency of sunscreen
application in either univariate or adjusted models. Similarly, the number
of sunburns during the trial (P = .70) or reported
lifetime burns (P = .79) did not contribute to the
fit of the model.
The usual amount of time spent outdoors was also associated with the
number of sunscreen applications per day, with those spending more than 4
hours outside being 50% more likely to apply sunscreen more than once (Table 4). People who reported having 2
or more sunburns during the 5 years of the trial were approximately twice
as likely to report more frequent daily sunscreen applications than those
who had not burned, even after adjustment for skin type and the amount of
time spent outdoors (PR, 1.85; 95% CI, 1.21-2.83). There was a somewhat paradoxical
association between skin type and daily application frequency, with people
who rarely burned reporting more frequent sunscreen applications than those
who were prone to sunburn.
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Table 4. Association Between Possible Predictors of Sunscreen Use and
Frequency of Sunscreen Application
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Associations with the quantity of sunscreen that people applied were
modified by their frequency of sunscreen use. Among those who used sunscreen
frequently, men applied 20% more sunscreen per square centimeter than women,
but the same association was not found among less frequent users (Table 5). In both groups, those aged between
40 and 59 years used the least sunscreen. The quantity of sunscreen frequent
users applied was inversely related to duration outdoors, whereas people who
used sunscreen less frequently applied more the more time they spent outdoors.
A number of indicators of sun-induced damage to the skin were examined, including
solar keratoses, solar elastosis, telangiectasia, and a history of skin cancer,
with solar keratoses being the only indicator of skin damage that was positively
associated with the quantity of sunscreen applied. People with a history of
sunburn during the trial applied more sunscreen to their skin than those with
no sunburn history.
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Table 5. Association With Quantity of Sunscreen Applied per Square
Centimeter of Skin, Stratified by Frequency of Sunscreen Use
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REASONS FOR NOT USING SUNSCREEN DAILY
Of the 393 participants in the intervention group who completed the
questionnaire and reported less than daily sunscreen use, 353 (90%) completed
the question concerning the reason for not using sunscreen on regular occasions.
Almost 50% of participants stated that they did not think sunscreen application
was necessary given the weather conditions or their planned activities. Of
these respondents, 45% reported that they generally spent almost no time outdoors
during the day, while 14% reported that they spent greater than 50% of their
time outdoors on average. All 5 participants who reported that they did not
use sunscreen because they wanted to obtain a tan were aged between 20 and
39 years, and 4 of the 5 were men.
COMMENT
Studies examining sunscreen application behavior have been numerous,
but most research has been conducted in selected people or in restricted settings
such as at the beach,13-14 in
schools,15-16 or in outdoor work.17 Most studies among randomly selected adult populations
ask specifically about the use of sunscreen "when outside in the sun" (eg,
Robinson et al18) despite the fact that this
may overestimate the proportion of time outside that the skin is protected
by sunscreen.6-7 The sunscreen
intervention of the Nambour Trial specifically required participants to apply
sunscreen every day, and more than half of the community participants were
able to adhere to this request or to apply it at least 5 days a week. However,
almost a quarter of the respondents to this question reported that they applied
sunscreen on 2 or fewer days per week. Further investigation showed that of
these "low-frequency" sunscreen users, 48% reported that they spent almost
no time outside on a typical day, but a further 40% spent at least some time
out of doors and 11% spent more than 50% of their time outside. When asked
the reason for their less frequent sunscreen application, many participants
reported that they "did not believe it to be necessary given their planned
activities"—presumably their outdoor activities entailed incidental
rather than intentional sun exposure. Similarly, among a group of students
holidaying in Europe, intentional sunbathing was associated with the total
sunscreen used while on holidays, but the total duration of outdoor exposure
was not.19 Addressing the apparent misconception
that no protection is required during frequent incidental exposures to the
sun may be one way for future primary prevention campaigns among highly exposed
adults to achieve better control of skin cancer.
Although the intention-to-treat analysis of the Nambour Trial5 showed that randomization to daily sunscreen use did
not increase the risk of skin cancer and was in fact protective for squamous
cell carcinoma, those within the intervention group who reported a high frequency
of sunscreen application were more likely to have had a skin cancer diagnosed
during the trial. This paradoxical association between sunscreen use and nonmelanoma
skin cancer or actinic skin damage has been reported previously20-21 and
is almost certainly due to uncontrollable "confounding by indication" resulting
from the highly complex interrelationship between phenotype, exposure factors,
and sunscreen use.21
The positive relationship found between sunscreen use and sunburns in
our study is consistent with results of previous reports. The SunSmart evaluation
in Victoria, Australia, reported that 46% of people who almost always used
sunscreen had been sunburned in the previous summer compared with only 31%
of those who rarely used sunscreen.6 Similarly,
there was a nonsignificant increase in risk of burning among children who
reported frequent sunscreen use.22 A Queensland
study found that, despite increased sunscreen use between 1988 and 1991, the
number of people reporting a sunburn the previous weekend had not decreased,
although the severity of the sunburns was lower.23 In
most cases the site and severity of the sunburn and the type of exposure during
which the burn occurred have not been investigated. Unavoidable confounding
by risk of burning is likely to partially explain the association.
The average weight of sunscreen used during the entire 5 years of the
trial varied widely in this population, with a median of 1.5 g/d. Among self-reported
higher users, however, this increased to a median of 2 g/d. There have been
a number of previous longitudinal studies of sunscreen use,19, 24-26 only
one of which reported comparable data.26 Participants
in the Australian trial evaluating sunscreen in the prevention of solar keratoses26 used a mean of 666 g of sunscreen during a 7-month
period, approximating a mean of 3.2 g/d, higher than our mean of 1.65 g/d.
This may have occurred because their study was of shorter duration and/or
because their participants were volunteers older than 40 years with at least
1 solar keratosis at baseline. The decreasing weight of sunscreen used during
the 5 years of our trial may have resulted from decreased frequency or thickness
of application. More frequent administration of questionnaires through the
trial would, in theory, have detected variation in sunscreen application frequency.
However, the accuracy of the reports might have been compromised by continued
involvement in the trial.
This is only the second study to examine the quantity of sunscreen used
per unit of skin surface area in a relatively unselected population of adults.
Evidence from the previous study19 is more
difficult to generalize to adults in community settings because the data pertained
to students aged 18 to 24 years who were on holidays. Other studies have been
among volunteers,27-28 nude sunbathers,29 and people with photosensitivity disorders.30 Two studies provided the sunscreens in smaller containers
than usual,30 and this has been shown to affect
the amount of sunscreen applied.31 In all but
3 studies,19, 26, 29 participants
were observed by investigators during their sunscreen application. The estimated
amount of sunscreen applied has ranged from approximately 0.55 mg/cm2 19, 29-30 to
1.0 mg/cm2, although this has varied with both the type of sunscreen
being applied27 and the site of application.30 We recognize the limitations in our study that result
from estimating the amount of sunscreen applied by community participants.
These include disregarding variations in the weight of sunscreen used in favor
of average weight per day and the assumption that estimated weight and frequency
were correct and that the reported frequency of application did not fluctuate
throughout the trial. We also lacked knowledge about the precise surface area
of application and about variations in amount used on different body sites.
Nevertheless, our estimation falls in the range of usage estimates from similar
studies. It is possible that our estimates of amount used are higher than
the recently published longitudinal study among students19 because
of the greater awareness of skin cancer risk among the Australian population.
Our study confirms previous reports that most sunscreen users are not achieving
the level of protection of the sun protection factor stated on the bottle.19, 28-29 A greater educational
focus on the adequacy of each application may partly resolve this problem,
although it is unlikely that most people will double the amount of sunscreen
that they naturally apply to their skin. Given the technical difficulties
and implications for education that would arise if sunscreen testing standards
required a more realistic testing thickness, we agree with Autier et al19 and Diffey32 that
more informative labeling of sunscreen bottles is long overdue.
This is the most complete set of prospective data on actual sunscreen
consumption and use patterns during a 5-year period among a community of adults
whose demographic characteristics and sun exposure are broadly generalizable.
Clearly the impetus to adopt sun-safe practices was higher in this trial population
than would be expected in the wider community. Nevertheless, these results
indicate that educational campaigns that specifically recommend daily sunscreen
application to target incidental exposures might significantly contribute
to the improvement of sun protection behavior, with continual advice needed
to promote maintenance of the behavior.
In April 2000, a group of experts convened by the International Agency
for Research on Cancer concluded that "sunscreens probably prevent squamous
cell carcinoma of the skin when used mainly during unintentional sun exposure."33 On the basis of current recommendations to use sunscreen
on an ad hoc basis, a national skin cancer primary prevention campaign in
a high-risk population such as in Australia is thought to be economically
worthwhile.1 Encouraging a daily sunscreen
application strategy is a highly effective and achievable method of ensuring
protection during unintentional sun exposure; reducing intentional exposure
will require a different approach.
AUTHOR INFORMATION
Accepted for publication February 12, 2002.
This study was supported by the Public Health Research and Development
Committee of the National Health and Medical Research Council of Australia,
Canberra, and the Department of Health and Aging, Canberra. Sunscreen was
supplied by Ross Cosmetics Aust Pty Ltd, Melbourne, Australia, and Woolworths
Ltd, Sydney, Australia.
We thank Anny Fourtanier and Romano Mascotto, PhD, for their valuable
comments on this article.
Corresponding author and reprints: Rachel Neale, PhD, Queensland
Institute of Medical Research, PO Royal Brisbane Hospital, Brisbane 4029,
Queensland, Australia (e-mail: rachelN{at}qimr.edu.au).
From the Population and Clinical Sciences Division, Queensland Institute
of Medical Research (Drs Neale and Green), and Australian Centre for International
and Tropical Health and Nutrition (School of Public Health), University of
Queensland (Dr Williams), Brisbane, Australia.
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