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   

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.     

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.     

Efficacy of broad-spectrum sunscreens against the suppression of elicitation of delayed-type hypersensitivity responses in humans depends on the level of ultraviolet A protection

Sunscreens have been designed to protect against sunburn and their efficacy has, therefore, been labeled by the so-called sun protection factor (SPF). Although this value is well determined using a standardized protocol and it affords a good evaluation of the protection against erythema it may be inadequate to provide a relevant measurement of efficacy against other biologic damages. This is particularly true when action spectra and threshold dose are different from those of erythema. In the case of ultraviolet (UV)-induced immune suppression, the action spectrum is not known, so it cannot be asserted that SPF may accurately predict the level of protection against this endpoint. We addressed this issue by measuring in human volunteers the ability of two broad-spectrum SPF 15 sunscreens with different ultraviolet A (UVA) protection levels, to prevent the alteration of the efferent phase of the local delayed-type hypersensitivity (DTH) response to recall antigens (Multitest Pasteur/Mérieux, Lyon, France) after acute solar-simulated UV exposure. We first determined the ultraviolet radiation (UVR) dose needed to induce a significant DTH inhibition in several groups of 15 volunteers. Two minimal erythemal doses (2 MED) were found to be the minimal immunosuppressive dose (MISD). As a result, the immune DTH response is reduced in average by 36%. The lower doses tested (0.5 and 1 MED) were ineffective. Sunscreen-treated groups were exposed to either 1 or 2 MED x SPF doses. As expected, no alteration in DTH response was observed in the groups exposed to 1 MED x SPF whatever the sunscreen applied. In contrast, after exposure to 2 MED x SPF, the DTH response remained unaltered in the group pretreated with the sunscreen product with the higher protection in the UVA range but was significantly suppressed by 55.7% in the group pretreated with sunscreen with a much lower protection in the UVA range. These data suggest that SPF may not be sufficient to predict the ability of sunscreens to protect from UV-induced immune suppression. Determining the level of UVA protection is particularly needed, as UVA seems to have a relatively low contribution to erythema but is highly involved in immunosuppression.     

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.     

Quantity of sunscreen used by European students

BACKGROUND: The ability of sunscreen products to delay sun-induced skin erythema is indicated by the sun protection factor (SPF), which is measured using an internationally agreed sunscreen thickness of 2 mg cm(-2). OBJECTIVES: To determine the thickness of sunscreen used under practical conditions. METHODS: In two double-blind randomized trials performed in five different places in Europe in 1997 and 1998, 148 18--24-year-old students received either an SPF 10 or an SPF 30 sunscreen to be used during their summer holidays. RESULTS: Complete, detailed data on quantities of sunscreen used and skin areas on to which sunscreen was applied were available for 124 students. The median thickness of sunscreen applied was 0.39 mg cm(-2). We found no variation in sunscreen thickness according to sex, skin phototype, study place or SPF. CONCLUSIONS: Our results indicate that most consumers do not benefit from the SPF indicated on sunscreen bottles, and do not support the idea that thickness of sunscreen applied would be greater if these products were cheaper. We suggest that information on ability of a sunscreen product to prevent sunburn should be adapted in order to reflect actual usage patterns.     

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.     

Uniformity of sunscreen product application: a problem in testing,a problem for consumers

BACKGROUND/AIMS: Testing of sunscreen products requires application of uniform films of product of defined thickness to test volunteers. In spite of the seeming importance of product application to defining sunscreen efficacy, there have been few studies determining how well uniformity is achieved. The purpose of this work was to evaluate the uniformity of sunscreen products of different sun protection factors (SPFs) and vehicles on a variety of substrates by in vitro testing techniques. The results of a variety of testing strategies are reported. METHODS: Five commercial sunscreen products of labelled SPF 4-50 were tested using a variety of substrates: Transpore Tape, Vitro-Skin trade mark, and lambskin condom. Two experienced sunscreen testers applied the products. In vitro SPFs were determined using an Optometric 290 analyser or an Optronic Laboratories OL754 spectroradiometer configured for this application. RESULTS: SPFs for several locations on each film applied to a substrate were determined and the mean SPF and RSD percentage of the mean calculated. For all substrates and testing techniques the average RSD percentage was 18.6, with a range of 10-40%. CONCLUSION: The expected uncertainty of SPF due to product application non-uniformity is 20% when applied under optimal test conditions. Clearly SPF tests reported by different laboratories must exhibit significant variability, because of product application non-uniformity.     

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.     

Effect of daily versus intermittent sunscreen application on solar simulated UV radiation-induced skin response in humans

BACKGROUND: Acute and chronic skin damage occurs as a consequence of solar UV radiation exposure. To diminish such skin damage, the dermatologic community advocates the daily use of sunscreens as part of a sun avoidance strategy. OBJECTIVE: We determined the effectiveness of a sunscreen product with a sunscreen protection factor (SPF) of 15 applied daily in preventing UV-induced histologic damage in human skin compared with the protection afforded by sunscreens with equal or higher SPF applied intermittently. METHODS: Twenty-four subjects were exposed to 2 minimal erythema doses of solar-simulated UV on 4 consecutive days. Three sunscreen products were applied to the buttock of each subject. One SPF 15 product was applied daily before exposure to UV and, to simulate intermittent product use, an SPF 15 or SPF 29 product was applied on 3 of 4 days, with one missed application on days 2, 3, or 4. Skin biopsy specimens were taken and processed for routine and immunohistochemical staining. Changes in number of sunburn cells and Langerhans cells as well as degree of inflammatory infiltrate and lysozyme immunostaining were determined. RESULTS: There was a statistically significant increase in the number of sunburn cells, degree of inflammation, and intensity of lysozyme staining, and there was a decrease in the number of Langerhans cells at sites where sunscreen application was missed as compared with unirradiated control and daily SPF 15 sunscreen-treated sites. CONCLUSION: Our data suggest that daily use of a sunscreen reduces the skin damage produced by UV exposure compared with intermittent use of equal or higher SPF products. The daily application of sunscreens in appropriate quantities reduces the harmful effects of solar UV radiation on skin. Compliance is essential for maximal benefit of sunscreens.     

022 308 excimer laser treatment of psoriasis

The COLIPA Standard for solar simulators was developed to insure that SPF tested in different laboratories was not different because of the solar simulator used. Indeed for products with lower SPFs 2-10, the solar simulator standard reasonably assures similar SPFs when tested in different laboratories. For products with SPFs greater than 15, the SPF for the same product could be tested at 15 in one laboratory but as an SPF 100 in another.
Differences in SPF due to solar simulator filtration will occur only for sunscreen products that exhibit absorption like cut-off filters. Products which generally absorb all UV wavelengths equally will not exhibit differences in SPF due to solar simulator filtration.
In addition because of different amounts of UVA allowed within the COLIPA standard, the actual response for a given exposure may in one laboratory produce persistent pigment darkening and in another a simple sunburn. Ways to correct this flaw will be examined.     

Sunscreen standards tested with differently filtered solar simulators

BACKGROUND: The COLIPA standard for solar simulators permits a range of spectral filtration. Published studies comparing the SPFs of sunscreen formulas show that a range of SPFs is generally expected between laboratories. Specifically, three studies determining the SPFs of sunscreen standards have been performed in a series of laboratories and differences exceeding 50% have been reported. No studies to date have specifically examined potential differences in performance of Standard Sunscreen Test Formulas with varying solar simulator spectra within the permitted range of optical filtration. METHODS: In a paired clinical trial, two SPF standard sunscreen formulas were tested using two solar simulators that complied with the COLIPA standard for solar simulators but were filtered differently. One solar simulator was filtered as supplied by the manufacturer and delivered a high percentage of UVB; the other solar simulator was modified by removing the visible absorbing filter to deliver energy more closely resembling sunlight in the UVA-1 part of the spectrum, with a lower percentage of UVB. RESULTS AND CONCLUSION: The result was that the SPF of each standard sunscreen was almost 50% greater with the unmodified solar simulator than with the modified solar simulator. In vitro evaluation of the sunscreen standards predicted similar differences due to the spectral differences of the solar simulators, which appears to rule out reciprocity failure. However, reciprocity failure of the control MEDs was observed. The total intensity of the modified lamp was approximately 3 times that of the unmodified lamp.     

UV-induced immune suppression and sunscreen

Sun protection factor (SPF) that measures sunscreen protection against erythema and edema may not be enough to measure a sunscreen's activity against many other biologic reactions induced by ultraviolet radiation (UV). It may be better to evaluate sunscreen efficacy using various tools including immune protection factor (IPF), mutation protection factor (MPF) and protection against photocarcinogenesis. In terms of immune protection, sunscreens protected against UV-induced immune suppression significantly. But protection in some cases was partial and often the IPF of sunscreens were less than the SPF. IPF may differ with various immunological endpoints, and it may be better to use a couple of different assays to measure sunscreen protection more objectively. Sunscreen use protects against most UV-induced non-melanoma skin cancers and actinic keratoses but its activity against melanoma is not clear. More studies with broad-spectrum stable sunscreens and better models for the investigation of malignant melanoma are required.     

Sun protection factor determination in vivo using a single exposure on sunscreen-protected skin

BACKGROUND: Determining sunscreen sun protection factors (SPFs) in a cohort of volunteers, particularly on products designed to provide high levels of protection, can be time-consuming. The conventional approach is to administer to each subject a series of exposures (normally between five and seven) on their sunscreen-protected skin. METHOD: A method, based on Gaussian statistics, is proposed that requires just a single exposure on the sunscreen-protected skin in volunteers to arrive at a reliable estimate of the mean SPF of a test product. RESULTS/CONCLUSION: The method is shown to yield an estimate of a product's mean SPF that is comparable, or better, in accuracy to estimates obtained by conventional multi-exposure testing.     

Sun protection factors: world wide confusion

The Sun Protection Factor (SPF) is a very popular instrument in the marketing of sunscreens. Unfortunately it is often not understood how sunscreens work and where the limitations of the SPF are. A lot of aspects of the SPF are confusing, e.g. the race for higher and higher numbers, the effect on SPF when less sunscreen is applied and if sunscreen should be used at all because they may block the Vitamin D synthesis. All this has a negative impact on compliance by the consumer or patient which is the most important influence factor in sun protection. This paper explains how sunscreens work, how the SPF is determined and where the limitations of the current methods exist. The dynamic view of 'UV radiation applied' and the 'UV dose transmitted' through the sunscreen onto the skin as well as onto a substrate in vitro help in the understanding and are also promising approaches in the in vitro assessment. A variation of the in vitro assessment of a sunscreen is the in silico calculation based on the absorption spectrum of the UV filters and an assumption about the irregular sunscreen film on the skin. The sunscreen simulator program can be used to determine how the SPF is affected by applying smaller amounts of sunscreen. Besides the SPF, UVA protection is also discussed. The degree of UVA protection determines the quality of the overall UV protection, whereas the SPF is an indication of the quantity of protection. Furthermore other protection factors such as IPF, iSPF, RSF and p53, and the inhibition of the Vitamin D3 synthesis by sunscreens are also discussed. In conclusion it is shown that the accuracy and robustness of the SPF and other Protection Factors will improve significantly with the availability of true broad-spectrum sunscreens rather than conventional UVB-biased sunscreens, because uniform protection profiles lead to protection independent of the action spectrum of the endpoint and the UV-radiation source.     

Sunscreens--the ultimate cosmetic

One decade ago, a sun protection factor (SPF) of 15 was considered a complete blocker of ultraviolet radiation (UV). The logic behind that cutoff point was that sunscreens with this SPF number would always prevent erythema and that preventing erythema would prevent all the ill effects of UV exposure. Today, we know that both of these assumptions were wrong and we tend to recommend higher SPF. Consumers apply only about one-quarter to one-half thickness of the layer of sunscreen material used to measure the SPF in the laboratory. That means that less than 50% of the SPF number claimed on the label is spread on the consumer's skin, meaning that a sunscreen with an SPF 30 will give the real protection of an SPF of 15. Therefore, recommend 60 when you want a real protection of 30! Significant injury, DNA damage, mutations, and carcinogenesis can and do occur also with cumulative suberythemal UV exposure. Thus, erythema induction, a criterion that defines SPF, is not a good indicator of UV damage. We also need higher SPF values to prevent the damage caused by suberythemal doses of UV. The value of the SPF claimed on the label is diminished by environmental factors that are not taken into account during SPF measurements in the laboratory, such as sweating, water immersion, rubbing off, and photodegradation. There are some misunderstandings and confusion about the mode of action of physical sunscreens. It was originally considered that, in contrast to organic sunscreens, the inorganic metal oxides (zinc oxide and titanium dioxide) acted as scatterers or reflectors of UV light, as a mirror. This is not the case with modern micronized forms of metal oxides. It has been shown that both zinc oxide and titanium dioxide mobilize electrons within their atomic structure while absorbing UV radiation. Thus, although metallic oxides are not inert per se, in their coated form they are stable, non-toxic, and safe and they act as highly efficient UV attenuators. Therefore, we recommend our patients to use this type of sunscreens. We should exert all our influence upon our patients not to expose themselves to excessive sunlight, to routinely use generous layers of sunscreen agents, and to wear protective clothing. To wait for the dust to settle around the issue of the effectiveness of sunscreens in preventing melanoma, while the ideal sunscreens--topical, systemic, whatever--are at our disposal, is a luxury we cannot afford.     

Sunscreen protection against cis-urocanic acid production in human skin

Commercial sunscreens may offer some protection from immunosuppression induced by ultraviolet (UV) radiation, but agreement concerning the degree of protection is lacking. Cis-urocanic acid, formed by the photoisomerization of transurocanic acid is considered an important mediator of the cutaneous immunomodulation resulting from exposure to UV radiation. We investigated the effect of sunscreens on the isomerization of urocanic acid in 17 human subjects. Two sunscreens containing chemical filters, sun protection factor (SPF) 4 and SPF 10, and a SPF 10 sunscreen with a physical filter were applied at a thickness of 2 mg/cm2. The effect of a thin layer (0.5 mg/cm2) of the chemical SPF 10 sunscreen was also evaluated, as the amount of sunscreen applied in practice may be considerably less than recommended. All areas were irradiated with a single UV dose of 3.6 SED (standard erythema doses). In irradiated unprotected skin the median net production of cis-urocanic acid was 52% (relative amount). In the sites treated with the chemical sunscreens, the production of cis-urocanic acid was 7.4% (SPF 4) and 3.5% (SPF 10), and isomerization was thus reduced more efficiently at a higher SPF (p<0.01). The physical sunscreen reduced the formation of cis-UCA to 15%, and was significantly less effective than both the chemical SPF 10 sunscreen (p<0.01) and the SPF 4 sunscreen (p<0.01). The production of cis-urocanic acid in the area treated with the thin layer of the chemical SPF 10 sunscreen was 22%. The protection against the production of cis-urocanic acid was therefore reduced significantly (p<0.01) when the sunscreen was applied in an amount lower than recommended.     

Reciprocity for solar simulators used in sunscreen testing

Reciprocity for sunscreen solar protection factors (SPFs) and for delayed erythema was examined using a solar simulator equipped with neutral density filters to vary the beam intensity. Similar SPFs were obtained over a 15-fold intensity difference, using a sunscreen with a low (SPF-4) and a high (SPF-15) protection factor. Reciprocity was also observed for delayed erythema in unprotected skin.     

Sunscreen protection in the ultraviolet A region: how to measure the effectiveness

Products containing ultraviolet (UV) radiation absorbing or scattering ingredients provide varying degrees of protection from sunlight (or other UV sources), thus minimizing the deleterious effects on the skin. The "sun protection factor" (SPF) of sunscreen products has become a well recognized indicator of protection against sunburn induced predominantly by ultraviolet B radiation (UVB: 290-320 nm). A similar system of denoting sunscreen protection from ultraviolet A (UVA: 320-400 nm) radiation has not been universally recognized. A variety of test methods have been proposed, both in vitro and in vivo, each with specific virtues and shortcomings. Regulatory agencies and industry have been reviewing the available methods over the past decade in an effort to develop consumer meaningful claims and appropriate substantiation methods. This article reviews these test methodologies, in vitro and in vivo, as well as the biological background that establishes the need for UVA protection, and the UVA content of solar radiation and its variability.