The relation between sun protection factor and amount of suncreen applied in vivo

BACKGROUND: The declared sun protection factor (SPF) is based on the use of a sunscreen layer of 2 mg cm(-2). However, only around a quarter (0 x 5 mg cm(-2)) of this amount is applied by sunbathers. Theoretical calculations have suggested that the effective SPF is related to sunscreen quantity in an exponential way but this was not confirmed in vitro and has not been studied in vivo. OBJECTIVES: To investigate the relation between SPF and sunscreen amount in vivo. SUBJECTS AND METHODS: On the backs of 20 healthy volunteers, five areas of 34 cm(2) each were marked. One area was phototested to determine the ultraviolet (UV) sensitivity. Four areas were treated with a sunscreen SPF 4 in different amounts: 0 x 5, 1, 2 and 4 mg cm(-2). Thirty minutes after sunscreen application a phototest was conducted on each area. The effective SPF was calculated 22-26 h after irradiation using the UV dose needed to produce just perceptible erythema (minimal erythema dose) on protected and unprotected skin. RESULTS: In all areas the mean SPF was significantly different from an SPF of 1 (no protection) (P 相似文献   

The influence of the amount of sunscreen applied and its sun protection factor (SPF): evaluation of two sunscreens including the same ingredients at different concentrations

Background: To estimate labeled sun protection factor (SPF) for sunscreen, the amount of product applied on volunteers, according to food and drug administration (FDA) and International protocols, is 2 mg/cm². However, different studies have shown that consumers actually apply much less product when exposed to the sun. Previous studies have reported contradictory findings in an attempt to correlate the amount applied in relation to SPF. The objective of the present study was to estimate the influence of the quantity of sunscreen applied in the determination of SPF, according to the FDA methodology.
Subjects and methods: Forty volunteers were included in two groups (SPF 15 and 30). The selected sunscreen was then applied in four different quantities (2, 1.5, 1.0 and 0.5 mg/cm²). All areas were irradiated with a solar simulator. After 24 h, the minimal erythemal dose (MED) and SPF were determined.
Results: In both groups, we observed that the SPF decreased when the amount of sunscreen applied was decreased. The differences between the 2 mg/cm² area and the others were significant in both groups ( P <0.001). The correlation between specified SPF and applied amount grew exponentially.
Conclusion: The protection provided by sunscreen is related to the amount of product applied. It is essential to educate consumers to apply larger amounts of sunscreen for adequate photoprotection.     

The comparison of sun protection factor values with different light sources.

Sun protection factors (SPFs) were evaluated with three light sources (sunlight, a xenon arc solar simulator, and fluorescent lamps) in indoor and outdoor studies. Two types of light, UV-A+B and UV+Visible, were obtained from the solar simulator. The untanned backs of twenty-four healthy male volunteers were used as test sites. A broad spectrum sunscreen containing SPF 6, according to the manufacturer, was used. The sunscreen tested was applied at 2 mg/cm2. The actual SPF values were 4.8 with sunlight, 6.0 with UV-A+B, 4.9 with UV+Visible, and 11.8 with fluorescent lamps. There were no significant differences between the SPF values with sunlight and those with the solar simulator; the SPF value for fluorescent lamps was significantly higher. The SPF with UV-A+B of the solar simulator was similar to that with sunlight; the use of this light served to reduce pain on tested subjects. Therefore, UV-A+B from the solar simulator seems to be the most appropriate artificial light source for evaluating sunscreens.     

New sunscreens confer improved protection for photosensitive patients in the blue light region

BACKGROUND: Some patients with photosensitivity disorders are sensitive to visible radiation. As current commercial sunscreens do not significantly absorb in this region, there is a lack of effective topical photoprotection. To meet this need a new range of sunscreens has been developed incorporating zinc oxide and pigmentary grade titanium dioxide as active ingredients. OBJECTIVES: To determine the effectiveness of the new sunscreens in providing protection for patients with visible radiation photosensitivity. METHODS: In the first part of this study, an in vitro transmission spectrum was obtained. The properties of the new sunscreens, as well as a range of commercial agents, were compared, and a new parameter, photosensitivity protection factor (PPF), was developed. This was used to predict the likely degree of protection the various sunscreens would provide for patients with photosensitivity extending into the visible region. In the second in vivo part of the study, patients with known visible (blue) light photosensitivity were tested using light at 430 +/- 30 nm and the protection factor (PF) at this wavelength was determined. RESULTS: Mean +/- SD PPFs for the new sunscreens were between 5.4 +/- 0.3 and 9.6 +/- 0.3, compared with 4.1 +/- 0.1 for Sun E45 (sun protection factor, SPF 25) and 4.2 +/- 0.1 for RoC Total (SPF 25). The derived in vivo PF for Sun E45 ranged between 1 and 4 (median 2). For the new sunscreens the range was 3 to > 10 (median 8). CONCLUSIONS: This study demonstrates that the new sunscreens do provide protection for patients with sensitivity to visible light (blue light region).     

Durability of the sun protection factor provided by dihydroxyacetone

BACKGROUND/PURPOSE: The sunless tanning agent dihydroxyacetone (DHA) is known to protect against longwave ultraviolet radiation (UVA) and visible light. Recently, our laboratory has shown that DHA in addition offers a modest sun protection factor (SPF) in humans. We conducted this study in order to investigate the durability of the SPF provided by DHA. METHODS: Ten healthy volunteers were treated with 20% DHA cream twice in three areas on the volar forearm. One, 5 and 7 days after the second application the participants were phototested with simulated sunlight in each area. Blue reflectance was used to measure the skin coloration by DHA in the test sites. RESULTS: DHA generated a significant SPF of 3.0 at day 1, 2.0 at day 5 and 1.7 at day 7 (P<0.0001). The SPF was positively correlated to the change in blue reflectance (r=0.39, P=0.034). The loss of SPF unit/day was not significantly different between the subjects (P<0.122). However, the intercepts were significantly different (P<0.0001) indicating differences in the initial SPF obtained among the subjects. CONCLUSIONS: The SPF of DHA decreases with the same loss of SPF unit/day between humans and the durability of the SPF thus depends on the initial SPF provided.     

Sun protection factor persistence during a day with physical activity and bathing

Background/purpose: The persistence of sunscreens during a day with physical activity and bathing is often debated. We wished to examine the durability of the protection achieved by one sunscreen application. Methods: Seven areas were marked on the back of 24 volunteers. One area was phototested to determine UV sensitivity. Six areas were treated with either an organic or an inorganic sunscreen (2 mg/cm²). The participants performed physical activities, were exposed to a hot environment and bathing during 8 h and were phototested with ultraviolet‐B (UVB) radiation 30 min, 4 and 8 h after sunscreen application. The minimal erythema dose (MED) was determined 24 h after irradiation. The sun protection factor (SPF) was calculated, as MED on protected skin/MED on unprotected skin. Results: The SPFs of the inorganic and organic sunscreen, respectively, were reduced by 38% and 41% after 4 h and by 55% and 58% after 8 h. Conclusion: One application of either an inorganic or an organic sunscreen reduced the erythema caused by UVB during a day with physical activity and bathing. After 8 h the sunscreens still provided approximately 43% of the initial protective effect. This might simulate what happens during a day at the beach.     

Sunscreen use and sun protection practices in students and personnel of Celal Bayar University

BACKGROUND/PURPOSE: The steady increase in the incidence of melanoma, non-melanoma cutaneous neoplasia and preneoplastic disorders has contributed to the demand for more effective protection from the sun. In this study, we aimed to determine the prevalence of sunscreen use and other sun protection behaviors in a large sample of students and personnel of Celal Bayar University, Manisa, Turkey. METHODS: The study group included 1018 participants of whom 607 work in the Celal Bayar University Hospital and 411 are students from the Medical Faculty and School for Health Professionals. All participants completed a questionnaire composed of 45 items about sun protection and other health behaviors, such as sports activity, use of cigarettes, alcohol and seat-belts. Sun protection factor (SPF) of sunscreen, avoiding sun exposure during peak hours, wearing clothing, a hat and sunglasses were studied. RESULTS: Of the 1018, 403 participants were male and 615 were female. While avoiding sun exposure during peak hours was the most popular preventive behavior for men (42.5%), wearing sunglasses was the most popular one for women (50.7%). Avoiding exposure was the second preventive behavior for women (42.1%). Use of sunscreen with SPF 15+ was the second popular protective measure for men (19.4%) and the third one for women (39.2%). There were no significant relationships between sun protection behaviors and obesity, use of cigarettes and alcohol. We also investigated behavioral changes with sunburn experience in the participants who had sunburn history. Among these behavioral changes, increased use of sunscreen and decreased sun exposure during peak hours with sunburn experience were significant. CONCLUSION: Our study demonstrated that the risk of sun exposure is largely unrecognized in Manisa, Turkey, and we have very incomplete information about protective measures. An efficient policy of education on the effective use of sun protection methods should be developed to prevent skin cancer.     

Sunscreen application by photosensitive patients is inadequate for protection

Photosensitive patients often comment that sunscreen products seem of little benefit. We used fluorescence spectroscopy to assess quantitatively their sunscreen application technique. A dose-response relationship for sunscreen skin surface thickness and fluorescence intensity was determined for an intrinsically fluorescent sunscreen, Neutrogena sun protection factor (SPF) 15. Ten women with long-standing photosensitivity conditions were asked to apply this sunscreen in the manner they would normally on a bright sunny day. Fluorescence measurements were taken from all unclothed body areas, comprising 17 sites of the head, neck, upper and lower limbs. Geometric regression analysis of the dose-response data showed a high level of correlation (r = 0.99) between sunscreen thickness and fluorescence intensity, allowing fluorescence measurements to be converted to an equivalent sunscreen thickness. The overall median sunscreen thickness was 0.5 mg/cm2, with median thicknesses of individual sites ranging from 0 to 1.2 mg/cm2. The most frequently missed sites were the posterior neck, lateral neck, temples and ears, all of which had median thicknesses of 0 mg/cm2. Hence, photosensitive patients fail to apply sunscreen in some prominently exposed sites, and use average thicknesses far less than the manufacturers' recommendation (2 mg/cm2). The level of protection is much lower than anticipated from the stated SPF of the product.     

Application of sunscreen − theory and reality

We present research on sunscreen use with possible pitfalls and discuss theory vs. reality. A literature review in PubMed was conducted using the terms ‘sunscreen application’, ‘sunscreen use’ and ‘sun protection factor’. The sun protection factor (SPF) of sunscreens are tested using a thickness of 2 mg/cm², but investigations show that sunscreen under natural conditions is applied insufficiently with amounts about 0.39 to 1.0 mg/cm², which decreases the protection factor considerably. It has been shown that early reapplication or use of very high SPF (70–100) may partly compensate for the discrepancy between the amounts of sunscreen applied during testing and in reality, and that sunscreen application can be improved by education of consumers. Missing areas and ultraviolet radiation exposure before sunscreen application are other pitfalls that reduce the protective effect of sunscreens considerably. Current sunscreen labelling overrates the protective effect of a given sunscreen when the reality of sunscreen use is taken into account. This may possibly mislead consumers to feel it is safe to extend sun exposure. Alternatively to educating people to use large amounts of sunscreen, we suggest a simple teaching strategy: (1) Apply before sun exposure and (2) Reapply once within 1 h.     

Children and sun protection

Sun protection is a central measure to avoid the development of skin cancer and premature aging of the skin. In this context skin protection of children is of particular relevance since children spend a lot of time outdoors and they cannot provide themselves with sun protection measures as adults can. In addition to this sunburn reactions in childhood are particularly important in the development of melanoma skin cancer. This special situation of children with regards to sun protection has not only become aware to dermatologists but also to politicians, which is why a recent recommendation of the European Union explicitly points out the necessity of stringent sun protection of children. This review summarizes the current knowledge about sun protection of children. Underlying mechanisms of skin carcinogenesis in children, available sun protection measures as well as practical advice on daily sun protection of children are discussed.     

Machine learning for the prediction of sunscreen sun protection factor and protection grade of UVA

We report a prediction model for sunscreen sun protection factor (SPF) and protection grade of ultraviolet (UV) A (PA) based on machine learning. We illustrate with real clinical test results of UV protection ability of sunscreen for SPF and PA. With approximately 2200 individual clinical results for both SPF and PA level detection, individually, we were able to see that active ingredient information can provide accurate SPF and PA prediction rates through machine learning. Furthermore, we included four new factors—presence of pigment, concentration of pigment grade titanium dioxide, type of formulation and type of product—as additional information for the prediction model and were able to see increased prediction rates as results.     

Sun protection factor persistence on human skin during a day without physical activity or ultraviolet exposure

Background/purpose: Recently, we showed that the sun protection factor (SPF) decreases by a constant factor to reach 55% during a day with activities. Organic sunscreens but not inorganic ones are absorbed through the skin. We wished to determine the SPF decrease caused by absorption by investigating the difference in SPF decreases between an organic and an inorganic sunscreen, assuming that the sunscreens are stable, and that the SPF decrease is time dependent if caused by absorption.
Methods: Sunscreens were used on the backs of 22 participants, who were physically inactive at 22 °C. SPF testing was performed 30 min, 4, and 8 h after application of 2 mg/cm² sunscreen. Whether cream evaporation changed the ultraviolet (UV) transmission was studied in vitro .
Results: The SPFs of the organic and inorganic sunscreens were reduced by about 25% after 8 h. Evaporation of the cream did not cause a change in UV transmission in vitro .
Conclusion: A similar decrease in SPF of the organic and inorganic sunscreen was seen during 8 h without activities, and is thus not likely to be caused by absorption or evaporation from the skin. The SPF decrease after 8 h is about 55% when the participants perform activities and 25% without activities.
Trial registration: Registered at http://www.clinicaltrials.gov . Register name: 'Sunscreen: Persistence of Sun Protection Factor and the Influence on Vitamin D'. Register number H-B-2007-120.     

Sun protection factor measurement of sunscreens is dependent on minimal erythema dose

This study investigates the influence of skin colour and minimal erythema dose (MED) on the in vivo determination of sunscreen sun protection factors (SPFs). The MEDs of groups of 10-20 subjects were measured on the lower back with a 1000-W solar-simulated xenon arc lamp. Five sunscreens, with commercially measured SPFs ranging from 4 to 30 + were then tested on the different groups, and their SPFs were correlated with volunteers' MEDs. We found that the sunscreens had higher SPF values when tested on subjects with lower MEDs and paler skin. The SPF values obtained with our ultraviolet (UV) source were lower than the SPF values reported with commercially used solar simulators. We conclude that while SPF tests with artificial UV sources and pale-skinned volunteers can and should be used to rank the efficacy of various sunscreens in preventing sunburn, they should not be interpreted as measures of a sunscreen's absolute level of sun protection. Factors such as the differences in skin colour and MED between subjects used for SPF testing and the general population, the spectral differences between sunlight and artificial UV, as well as the tendency of the public to apply only small amounts of sunscreen and to re-apply it infrequently, mean that laboratory and sunlight SPFs may be markedly different.