Sunscreen use and failures – on site observations on a sun-holiday

Abstract

With this observation study we aimed to determine how and when sunscreen was used. 20 sun seekers were observed during a one-week sun holiday in Hurghada, Egypt. The sunscreen application thickness was related to part of body, time outdoors, exposure to ultraviolet radiation and to sunburning. Skin sites with sunscreen were exposed to UVR significantly longer and received significantly higher UVR doses than skin sites without sunscreen. They received an average of 0.62 SED [0.0–9.3 SED] (13% of their MED) before the first sunscreen application of the day. The average sunscreen used was SPF15 and the sunscreen application thickness was in average 0.79 mg cm⁻2 giving an approximated effect of SPF3. For different body parts either the total UVR exposure dose or the UVR exposure time and UVR exposure dose before the first sunscreen application were higher for sunburned than non-sunburned skin sites. In the final model gender, skin type and UVR to skin (adjusted for SPF and sunscreen application thickness) were significant predictors of sunburning. The sunscreen application thickness of 0.79 mg cm⁻2 was less than the 2 mg cm⁻² used for testing SPF. The late start of sunscreen use and improper application thickness was ineffective in preventing sunburn, and therefore could not compensate for the risk of prolonged UVR exposure and high UVR doses. Our results lead us to suspect that the protective effect of sunscreen use against DNA-damage, and thereby skin cancer, is minimal the way sunscreen is used under real sun holiday conditions.

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Introduction

Sunscreens are recommended to protect the skin from the effects of harmful solar ultraviolet radiation, such as erythema. Sunscreen may even diminish cellular damage from suberythemal ultraviolet radiation doses and may thereby delay long-term skin damage and skin cancer.¹ Erythema is considered a clinical surrogate for DNA-photo-damage, and the sun protection factor (SPF) can be considered comparable to the DNA protection factor.² A study where volunteers were irradiated with 0.5 minimal erythema dose (MED) 19 times over 4 weeks showed that p53 expression was markedly reduced in volunteers protected with a broad-spectrum daily care product (SPF8/UVA-PF7), concluding that sunscreens can prevent the “silent” sub-erythemal cumulative effects of ultraviolet radiation.³ The use of sunscreen has also been found effective in reducing the number of squamous-cell carcinomas in a follow-up of 4.5–8 years,^4,5 and to prevent the development and hasten the remission of solar keratoses among healthy subjects,⁶ and among organ transplant patients.⁷ It may even be able to prevent the development of melanoma.⁸ To obtain the labelled sun protection factor of a sunscreen 2 mg cm⁻² should be applied.^9,10 The actual amount applied has been shown to be 50%, or less, than needed to achieve the labelled SPF.^11–15 One laboratory study added dihydroxyacetone (as a fluorescent) to a sunscreen, allowing calculation of the amount of sunscreen applied, which was about 1 mg cm⁻².¹¹ Two studies gave complimentary sunscreen to volunteers and weighed the bottles every third month. By registering the amount of sunscreen used and using diary registrations of the skin area with sunscreen, the median amount of sunscreen was calculated as 0.39 and 0.79 mg cm⁻², respectively.^12,13 Even photosensitive patients applied insufficient amounts of sunscreen (0.5 mg cm⁻²) in a laboratory study using fluorescence to evaluate the amount applied.¹⁴ Lastly, a real-life study where volunteers were recruited for one day on the beach found the amount of sunscreen applied was 0.5 mg cm⁻² by weighing sunscreen bottles before and after a full-body sunscreen application.¹⁵ It has also been shown that sunburns are more frequent on days with sunscreen use.^16,17

We found it important to investigate how sunscreen is used in a real-life situation when protection is most crucial: during a sun-seeking holiday. We aimed to determine the exact amount of daily-applied sunscreen by weighing the sunscreen bottles every day and through diary registrations, calculating the sunscreen application thickness on different skin sites. Additionally the relation between sunscreen use, sunburns, ultraviolet radiation (UVR) doses and time outdoors was analysed.

Method

Definitions

Participation days: 20 sun-seekers participated for 6 days, totalling 120 participation days.

Skin-site observations/skin-site observation days: We assessed 6 skin sites: head, including face, ears and scalp; chest; midriff; back/shoulders; arms; and legs, on each of the 20 volunteers for 6 days, totalling 720 skin-site observations/skin-site observation days.

Sunburn: Any site with sun-induced erythema present the following morning.

Pigment protection factor (PPF): Is measured by skin reflectance and represents the number of standard erythema doses (SED) needed to provoke a minimal erythema dose (MED) and is therefore a measure of the skin's sensitivity to the sun. A PPF of 4 means that the MED is 4 SED, which is typical of a fair skinned person. PPF is linearly dependent on pigmentation and is calculated from this using a spectroscopic approach.^18–20

Standard erythema dose (SED): The term standard erythema dose refers to erythemal effective radiant exposures from natural and artificial sources of UVR. 1 SED is equivalent to an erythemal effective radiant exposure of 100 J m⁻². Standard erythema doses are independent of individual sensitivity to ultraviolet radiation.²¹

UVR exposure time: Daily time with UVR exposure on a skin site without clothing.

UVR exposure dose: Daily UVR dose on a skin site without clothing.

Volunteers

We recruited 20 volunteers (10F and 10M, mean age 44.3 years [range: 20–63]) through our hospital's intranet. A written informed consent was obtained from all volunteers.

The volunteers determined their skin type according to Fitzpatrick,²² resulting in skin type II = 12, skin type III = 6 and skin type IV = 2.

The inclusion criteria were: sun-seekers of Scandinavian ancestry defined as those who had been on at least 5 sun-seeking holidays south of Paris, France in the previous 10 years; ability to read Danish; and willingness to participate in pre- and post-holiday examinations.

The exclusion criteria were: psoriasis or active eczema, present or previous skin cancer, diseases with increased UVR sensitivity, organ transplant recipients, being disabled, and intake of photosensitizing medicine. All costs of the holidays were covered by the project grant to enhance compliance.

Setting

The study was performed during the first week of December 2010 at a holiday resort of “Hurghada”, Egypt (27.2°N, 33.5°E).

Study design

The volunteers arrived in Egypt in the late afternoon of December 2nd, 2010, when sunscreen bottles were weighed. The volunteers were instructed to behave as they normally would on a holiday with the addition of completing a diary, reporting for a skin examination every morning and for sunscreen bottle weighing every evening. The volunteers used their personal sunscreen and no instructions were given on how or where to apply it. The first skin examination was in the morning of December 4th and the final skin examination was on the morning of December 9th, 2010, shortly before returning to Denmark, giving 6 full study days. All 20 volunteers completed the study and complied with all the requirements.

Sun-exposure diary

The volunteers were asked to report sunscreen use inclusive SPF for each skin site and to report their clothing with a code for upper and lower body (see Table 1). Head and chest were considered exposed by any clothing code: midriff with clothing code 1 and back/shoulders with clothing code 1 or 2 for upper body, while arms and legs were considered exposed by clothing code 1, 2 or 3 for upper or lower body, respectively. Diary entries had to be made every 30 minutes from 07:00–18:30. The diaries were collected on site every evening and corrected with help from the volunteers. UVR exposure time and UVR exposure dose for a specific skin site comes from the registrations in the SunSaver adjusted by clothing code in the diary.

Table 1 The clothing codes from the diary and the definition of each number

Clothing code	Upper body	Lower body
1	Naked or bikini	Naked or bikini/speedos
2	Tank top	Shorts or short skirt
3	Short sleeves	Knee long shorts or skirt
4	3/4 long sleeves	3/4 long trousers or skirt
5	Long sleeves	Long trousers or skirt

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Daily examinations

The volunteers had a skin examination with assessment of erythema each morning. The same researcher did all the examinations. Any erythema was noted on a registration form for each skin site. To minimize any effects on the volunteers’ behaviour, they were not informed of the results of the researcher-assessed erythema.

Sunscreen registration

To register the amount of sunscreen used by a volunteer, we weighed the sunscreen bottles every night. Only the total amount of sunscreen used per day per volunteer is known, as one bottle of sunscreen could be used by only one volunteer but on as many skin sites as desired. Accordingly, we know on which skin sites the sunscreen was used, but we do not know the exact amount of sunscreen used per site. If a volunteer used sunscreens with different SPFs, we summed the amount of each sunscreen. The volunteers were not informed of their daily sunscreen consumption.

Calculation of sunscreen application thickness

We calculated how many milligrams of sunscreen each participant applied per square centimetre. To do this we had to know their body surface area (BSA). We calculated their BSA by using the Mosteller formula, BSA (m²) = ([Height (cm) × Weight (kg)]/3600)^1/2.²³ We also had to determine the percentage of the BSA each skin site constituted. For this, we used a modified version of Augustsson et al.'s model²⁴ given as 6% for the head: face, scalp, and back of head; 15% for the arms, including hands; 38.5% for the legs; 14% for the front of the body: chest and midriff; and 14% for the back: back and shoulders. The last 12.5% is constituted by the soles of the feet, hair and body parts covered by swimwear, where sunscreen is usually not applied.

In the final calculations of mg cm⁻² for each participation day, we divided the total amount of sunscreen used that day by the total skin area where sunscreen had been applied. If sunscreen had been applied to a skin site more than once a day, the area percent of a skin site was multiplied by the number of applications. If a participant had registered use of a specific sunscreen, but the bottle weighed the same as on the previous day, the application thickness was registered as 0 mg cm⁻².

Formula 1: Average sunscreen application thickness (mg cm ⁻² ) on a specific participation day:

Amount of sunscreen used (mg)/total skin area with sunscreen application (cm²)

For each skin site the average sunscreen application thickness on a day was multiplied by the number of applications on that skin site, giving:

Formula 2: Sunscreen application thickness on a skin site for a day (mg cm ⁻²):

Average sunscreen application thickness (mg cm⁻²) × no. of applications on that skin site

The effective SPF was calculated for each skin site on each participation day by using the average SPF and the application thickness for that skin site, assuming an exponential growth.²⁵

Formula 3:

Effective SPF = SPF^{(Average sunscreen application thickness/2)}

In all the analyses of sunscreen (SPF, skin area, amount and application thickness) only participation days with sunscreen use were included.

Personal electronic UVR dosimeter “SunSaver”

Volunteers wore a personal electronic UVR dosimeter from sunrise to sunset. They were instructed to wear the UVR dosimeter uncovered on the dorsal aspect of the right wrist, replacing their usual wristwatch. The UVR dosimeter records time logged UVR data continuously and comprises a sensor and a data logger. It is an updated version of the UVR dosimeter (SunSaver).²⁶ A silicon carbide photodiode (JEC1I-DE ERYCS 2; Laser Components; Germany) was chosen as a sensor, which is sensitive only in the range 200–400 nm. The sensor has a built-in diffuser and a cosine response. The spectral response is similar to the CIE erythema action spectrum.²⁷ The data logger controls the sensor, which was set to measure every 5th second and to store an average of the last 24 measurements every 2 minutes along with the time of day. The measurement range of the dosimeter is 0.03 to 30 standard erythema doses (SED)/hour. The UVR dosimeter is battery driven.²⁶ Every evening data from the SunSavers were downloaded to a computer to store and to control data quality.

Time spent outdoors or the UVR exposure time for a skin site is calculated from time registrations in the SunSavers.

UVR to the skin (without clothing adjusted for SPF)

We made calculations of the daily UVR dose affecting the skin.

The UVR exposure dose after applying SPF was divided by the effective SPF

Adjusted

UVR

dose after SPF = UVR dose after SPF/Effective SPF

and finally

UVR to the skin = Adjusted dose after SPF + UVR dose before SPF.

Statistical analyses

SPSS Statistics 18 (PASW) was used for data analysis. The Kolmogorov–Smirnov test was used to test for normality of distribution. For the normally distributed data, t-test or linear regressions were used. The Mann–Whitney test was used to test unpaired data, which were not normally distributed. For relations between categorical data, Fisher's exact test was used, and for correlations between continuous data Spearman's or Pearson's test was used. A binary logistic regression was used to analyse the relation between sunburn and UVR to the skin, gender and skin type. The significance level was p < 0.05. Because of illness (stomach infection), 3 days with zero measurements were excluded from the analyses.

Ethics committee

The Danish Ethics Committee approved the study, H-D-2009-034-23449.

The study was conducted according to the principles of the Declaration of Helsinki.

Results

Skin type

The constitutive skin type on the buttocks of the volunteers was measured by a skin reflectance meter (UV Optimize Scientific 558; Chromo-Light, Espergaerde, Denmark).²⁸ PPF (pigment protection factor, see definitions) represents the number of SED (standard erythema doses, see definitions) needed to provoke a minimal erythema dose (MED) and is therefore a measure of the skin's sensitivity to the sun.¹⁹ The median PPF was 3.9 [range: 2.4–6.2], which means that 3.9 SED was expected to give erythema to the average skin type of our volunteers.

Time outdoors

From 07:00 to 18:30 women and men spent a median of 6.6 [range: 1.8–8.8] and 6.7 [range: 1.1–8.8] hours outdoors, respectively, and between 12:00 and 15:00 both men and women spent 2.7 [range: 0.0–3.0] hours outdoors. There were no significant differences between genders (p > 0.513). No difference was found in time spent outdoors between volunteers with or without sunscreen use (p = 0.445/p = 0.777). Whereas exposed skin sites with sunscreen were exposed to UVR significantly longer (median = 6.2 hours [range: 1.5–8.8]) than those without sunscreen (median 5.9 hours [range: 0.9–8.7 hours]) (P = 0.005).

UVR doses

Women received a median of 4.5 SED [range: 0.8–13.2] per day and 22.1 SED [range: 16.9–60.4] in total, while men received 5.3 SED [range: 0.5–14.5] per day and 37.6 SED [range: 15.8–47.8] in total. There were no significant differences between genders (p > 0.245).

The median UVR dose on days with sunscreen on at least one skin site was 5.0 SED [range: 0.8–14.5]; on days without sunscreen use, the median UVR dose was 4.8 SED [range: 0.5–9.2], the difference was not significant (p = 0.189). When comparing all skin site observations with and without sunscreen, we found a significant difference in the median UVR exposure dose: 4.8 SED [range: 0.0–14.5 SED] versus 4.3 SED [range: 0.0–12.2 SED] (p = 0.001). There was a positive correlation between UVR doses and time spent outdoors during 07:00–18:30 (p = 3.3 × 10⁻¹¹, r = 0.564) and 12:00–15:00 (p = 3.3 × 10⁻⁹, r = 0.513).

Sunscreen and SPF (sun protection factor)

The women's group had a total of 8 days and the men's group had 13 days without sunscreen use on any skin site. Sunscreen was applied on 68% of the 720 skin-site observation days. Women applied sunscreen on 72% and men on 64% of the skin-site observation days (p = 0.037). The average SPF used was 15. There was a statistically significant difference between SPF on sunburned skin sites and on non-sunburned skin sites, SPF13 and SPF15 respectively (p = 0.000002), but this makes no clinical difference.

Skin area, amount and application thickness of sunscreen

During the 6 study days the application thickness of the sunscreen was unchanged (p = 0.633), but the skin area with sunscreen and accordingly the amount of sunscreen diminished significantly (p = 0.033/p = 0.0002). There was no significant difference between men and women in skin area (cm²) with sunscreen (p = 0.512) or in the amount used (p = 0.082). The BSA for men was higher than for women (p = 0.004), so sunscreen was applied to a smaller part of men's skin area. The average application thickness of the sunscreen layer was 0.79 mg cm⁻², lowering the average SPF15 to an approximately effective SPF3. For women it was 0.66 mg cm⁻² (effective SPF2.4) and for men it was 0.93 mg cm⁻² (effective SPF3.4) (p = 0.022).

The average application thickness per day on the different skin sites was: head = 1.2 mg cm⁻², chest = 1.0 mg cm⁻², midriff = 0.9 mg cm⁻², back/shoulders = 0.96 mg cm⁻², arms = 1.0 mg cm⁻², and legs = 0.95 mg cm⁻².

Sunscreen and UVR exposure time and UVR exposure dose

The number of applications on a skin site on a specific day was dependent on UVR exposure time for that skin site (p = 0.003, R² = 0.017), but not on UVR exposure dose. In contrast the mean SPF on a skin site was dependent on the UVR exposure dose (p = 0.004, R² = 0.017), but not on UVR exposure time. The effective SPF was neither dependent on UVR exposure time or UVR exposure dose (p = 0.152/p = 0.422).

Time of sunscreen application and UVR-doses

The first sunscreen was in average applied at 09:22 h, the second application at 12:10 h and the third at 13:18 h. No difference was found in time of applications between different skin sites. The average time from the first UVR measurement on the dosimeter until the first sunscreen application was 51 minutes [range: 0–390 minutes]. In this time interval the average UVR-dose received was 0.62 SED [range: 0.0–9.3 SED], which in average was 13% [range: 0–234%] of the volunteers buttock-PPF (minimal erythema dose), and in average 10% of the daily UVR dose.

Sunburn

We observed sunburn on 194 of the total 720 skin-site observations (head = 60, chest = 70, midriff = 16, back/shoulders = 34, arms = 8, and legs = 6). When analysing all skin sites together, men were sunburned significantly more often than women were (men = 118/360, women 76/360, p = 0.001), and this was the case for all skin sites, except for the chest where women were sunburned more often than men.

Sunscreen to sunburned skin

Sunscreen was applied to 69% of the skin sites with sunburn and to 62% of the skin sites without sunburn (Fisher's exact test: p = 0.140). The number of applications was significantly higher and the SPF significantly lower on sunburned skin sites than on non-sunburned skin sites (p = 0.024/p = 7.9 × 10⁻⁵), but there was no difference in the application thickness of the sunscreen.

Sunburn related to sunscreen used before sunburn

We did not find any relationship between sunscreen use or no sunscreen use and the number of sunburn days for any skin site or in total (Table 2). Men had a significantly higher number of sunburns than women did, both on days with and without sunscreen (p = 0.005/p = 0.029).

For all skin sites with sunscreen applied we made a comparison of several variables between skin sites determined with or without sunburn. We compared the total UVR exposure time and UVR exposure dose, and the UVR exposure time and UVR exposure dose before and after the first sunscreen application from the day previous to the sunburn (Table 3).

Table 2 Number of total 720 skin-site observations with or without sunscreen applied and with/without sunburn. M = men and W = women

Skin sites	Skin site observations								Relation between sunscreen use and sunburn (p-value)
	N = 720
	Sunscreen				No sunscreen
	N = 491				N = 229
	Sunburn		No sunburn		Sunburn		No sunburn
	M	W	M	W	M	W	M	W
The last column shows that no statistical relation was found between sunburn and sunscreen use. Significant when p < 0.05.
Head N = 120	30	16	16	33	11	3	3	8	0.654
Chest N = 120	26	31	15	19	13	7	6	3	0.129
Midriff N = 120	10	0	28	39	5	1	17	20	1.0
Back/shoulders N = 120	11	8	27	33	10	5	12	14	0.200
Arms N = 120	2	3	36	39	3	0	19	18	1.0
Legs N = 120	1	1	30	37	3	1	26	21	0.400
Total skin sites	80	59	152	200	45	17	83	84	0.242

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Table 3 The UVR exposure time and the UVR exposure dose in total, before and after sunscreen application for sunburned and non-sunburned skin sites

	Head		p-Value	Chest		p-Value	Midriff		p-Value	Back/shoulder		p-Value	Arms		p-Value	Legs		p-Value
The data and analyses in this table only include skin-site observation days with sunscreen (494 cases). Significant when p < 0.05 and marked with *.
Sunburned 1 = Yes, 0 = No	0	1		0	1		0	1		0	1		0	1		0	1
Total UVR exposure dose (SED)	5.2	6.4	0.092	5.7	5.9	0.599	4.9	7.3	*0.05	4.7	6.4	*0.047	5.5	8.1	0.065	5.7	6.3	0.604
Total UVR exposure time (hours)	6.4	6.9	*0.032	6.5	6.7	0.561	4.3	5.6	*0.009	4.9	5.9	*0.043	6.1	6.9	0.610	6.2	6.9	0.703
UVR exposure dose before SPF (SED)	0.7	0.5	0.481	0.4	0.8	*0.042	0.4	0.8	*0.028	0.9	0.9	0.381	0.5	2.8	*0.003	0.5	0.2	0.784
UVR exposure time before SPF (hours)	1.1	1.1	0.237	0.7	1.2	*0.038	0.3	0.7	*0.034	0.7	0.7	0.441	0.9	2.6	*0.004	0.8	0.6	0.926
UVR exposure dose after SPF (SED)	4.6	5.9	*0.033	5.3	5.2	0.912	4.5	6.5	0.077	3.8	5.4	*0.024	5.0	5.2	0.856	5.2	6.1	0.518
UVR exposure time after SPF (hours)	5.3	5.8	0.261	5.8	5.5	0.287	4.0	5.0	0.072	4.2	5.1	0.054	5.3	4.2	0.138	5.4	6.2	0.578

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For head, chest, midriff, back and arms we found that the behaviour of the previous day was a significant determining factor for sunburns. Midriff, chest and arms with sunburn were significantly longer exposed (p < 0.038) and received significantly higher UVR doses (p < 0.042) before the first sunscreen application than those without sunburn, whereas head and back with sunburn received significantly higher UVR doses after the first sunscreen application and in total (p < 0.033). Legs were only found sunburned on 2 of the skin site observations with sunscreen, which might explain why no statistically significant differences were found between any variables (Table 3).

Modelling of risk to sunburn

With a binary logistic regression analysis of skin sites with sunscreen application we analysed the impact of UVR to skin, skin type and gender on the risk of sunburning. We found that high UVR to the skin (adjusted for SPF and sunscreen application thickness), low skin type and male gender were significant risk factors of sunburning: UVR to skin (p = 0.001, OR = 1.178, CI = 1.073–1.292), skin type (buttock-PPF) (p = 9.95 × 10⁻⁵, OR = 0.715, CI = 0.597–0.855) and gender (p = 0.007, OR = 0.573, CI = 0.382–0.861), but the model was not very strong (Cox and Snell R² = 0.062, Nagelkerke R² = 0.089).

Discussion

Previous studies of application thickness of sunscreen were conducted in laboratories or on beaches or they were distant long-term studies (volunteers returning sunscreen bottles to be weighed every third month), all with the uncertainty inherent under such conditions.^11–15 We conducted a real-life sun-holiday study determining amount of sunscreen used and time of application, relating it to gender, time outdoors, UVR-doses and number of sunburns by daily observations of our volunteers. Every year the Danish charter business alone is selling 600 000 travels to sunny destinations with the express aim of sunbathing and tanning, a considerable number for a Danish population constituting only 5.5 million people. We believe that our volunteers are representative of this sun-seeking population.

Skin sites with sunscreen were exposed to UVR significantly longer and received significantly higher UVR exposure doses than those without, and even before sunscreen application they daily received 0.62 SED in average (in average 13% of their MED). The average application thickness of sunscreen in our study was 0.79 mg cm⁻², which is similar to previous findings. One study proposed a linear relation between the amount applied and the SPF,²⁹ while several studies have found the relation between SPF and sunscreen amount to follow an exponential growth,^30–32 accordingly, application of 0.79 mg cm⁻² SPF15, as applied in our study, corresponds to an effective SPF of approximately 3. The application thickness of the sunscreen did not change throughout the week, maybe because individuals did not change their method of application, whereas the area with sunscreen and the amount of sunscreen decreased, possibly because the volunteers felt protected by their increasing pigmentation or because they wanted to increase their response to UVR-exposure (by pigmentation) before the end of the vacation. It is uncertain if the volunteers, as recommended, reapplied sunscreen after swimming or how much of the sunscreen remained on clothes or towels.

As we surprisingly did not find a statistically significant relationship between sunscreen use and sunburn, we felt encouraged to continue with analyses of relevant variables among all the skin site observations with sunscreen. Analysed separately for each skin site we found that either the total UVR exposure dose or the UVR exposure time and UVR exposure dose before the first sunscreen application was statistically significantly greater on sunburned skin site observations than on non-sunburned skin sites. Finally we found that male gender, lower skin type and higher UVR to the skin were statistically significant risk factors of sunburning. Our results indicate that even though the average UVR exposure dose received before the first sunscreen application only was about 13% of the tolerated dose, the time of sunscreen application is of importance, and that sunscreen use does not allow unlimited exposure to UVR, especially not for individuals with a sensitive skin type. Our results and the fact that the model was not very strong might partly reflect the limitations of our study. We do not know the quality of the volunteer's sunscreen application, if they applied sunscreen on the whole skin site, if they applied the sunscreen exactly where they were sunburned, how the UVR doses were distributed on the body during time (position in the sun), etc., but we believe we came as close to these parameters as possible in a real life setting. There seems to be a difference between genders, but no clear explanation of it. Men had a higher number of sunburns than women, both on days with and without sunscreen use, women used sunscreen more often, but men applied sunscreen in a 41% thicker layer than women did, whereas women possibly are more confident and thorough with application of cream. It is notable that the volunteers did not change their use of sunscreen on sunburned skin sites.

For all the volunteers the application thickness of the sunscreen was less than for SPF testing. The volunteers who intended to stay in the sun for a prolonged period attempted to protect themselves from sunburn by using sunscreen, but the improper use of sunscreen according to time of application and application thickness was ineffective in preventing sunburn and could not compensate for the risk of prolonged UVR exposure and high UVR exposure doses. Our results lead us to suspect that the protective effect of sunscreen use against DNA-damage, and thereby skin cancer, might be minimal the way sunscreen is used under real sun holiday conditions.

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Footnote

† This article is published as part of a themed issue on current topics in photodermatology.

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