Abstract:
Ultraviolet radiation (280-400 nm)-induced suppression of cutaneous cell-mediated immunity plays an important part in the development of skin cancer. Sunscreens are widely advocated to protect against skin cancer but if they offer insufficient protection against immunosuppression they may inadvertently increase skin cancer risk. This human study evaluated immunoprotection afforded by a commercial sunscreen preparation (labeled sun protection factor 15) offering primarily ultraviolet B (280-320 nm) protection. Indirectly, it also investigated whether ultraviolet A (320-400 nm) plays a part in ultraviolet radiation-induced immunosuppression. Healthy white-skinned volunteers were used (n=119). Ultraviolet radiation exposures were on previously unexposed buttock skin with an ultraviolet radiation source that complied with European recommendations for sunscreen testing. Ultraviolet radiation dose-response curves for sunburn/erythema and suppression of the contact hypersensitivity response were generated either with or without sunscreen in vivo and protection factors were derived for both end-points. The ultraviolet radiation wavelengths transmitted by the sunscreen were determined in vitro and showed that the sunscreen was primarily an ultraviolet B absorber, with relatively poor absorption in the ultraviolet A region. The sun-screen protected against both erythema and immunosuppression but protection against immunosuppression (IPF=4.9, 95% confidence interval: 2.3-10.6) was less than half that for erythema (Ery-PFg=14.2, 95% confidence interval: 10.2-19.8). Failure of the sunscreen to afford comparable protection against both end-points was probably due to immunosuppression by ultraviolet A, a part of the solar spectrum that does not readily cause sunburn. The sunscreen protected against both end-points, which supports the use of sunscreens to reduce immunosuppression but protection against immunosuppression may be improved if sunscreens are formulated to offer equivalent protection against ultraviolet B and ultraviolet A.

Abstract:
The photostabilities of a random set of commercially available sunscreen lotions and their active ingredients are examined spectroscopically subsequent to simulated sunlight UV exposure. Loss of filtering efficacy can occur because of possible photochemical modifications of the sunscreen active agents. Changes in absorption of UVA/ UVB sunlight by agents in sunscreen lotions also leads to a reduction of the expected photoprotection of human skin and DNA against the harmful UV radiation. The active ingredients were investigated in aqueous media and in organic solvents of various polarities (methanol, acetonitrile, and n-hexane) under aerobic and anaerobic conditions. The UV absorption features are affected by the nature of the solvents with properties closely related to oil-in-water (o/w) or water-in-oil (w/o) emulsions actually used in sunscreen formulations, and by the presence of molecular oxygen. The photo stabilities of two combined chemical ingredients (oxybenzone and octyl methoxycinnamate) and the combination oxybenzone/titanium dioxide were also explored. In the latter case, oxybenzone undergoes significant photodegradation in the presence of the physical filter TiO2.

Abstract:
Background: There are considerable data to suggest that protection from solar ultraviolet (UV) radiation will reduce the risk of acute and chronic skin damage in humans. Whereas the sun protection factor (SPF) provides an index of protection against erythemally effective solar UV largely confined to the UVB (290-320 nm) and short-wavelength UVA (320-340 nm) region, there is currently no agreed-upon method to measure broad-spectrum protection against long-wavelength UVA (340-400 nm).

 

Objective: The objective of these studies was to assess the potential of in vitro UV substrate spectrophotometry and subsequent calculation of the "critical wavelength" value as a measure of broad-spectrum UV protection and as a routine, practical procedure for classification of sunscreen products.

Methods: The spectral absorption of 59 commercially available sunscreen products and multiple experimental formulas with one or more UV filters was measured. Sunscreen product, 1 mg/cm(2), was applied to a hydrated synthetic collagen substrate, preirradiated with a solar simulator; and then subjected to UV substrate spectrophotometry. Multiple determinations from 5 independent samples per product were used to calculate the critical wavelength value, defined as the wavelength at which the integral of the spectral absorbance curve reached 90% of the integral from 290 to 400 nm.

 

Results: We found that a recognized long-wave UVA active ingredient such as titanium dioxide, zinc oxide, or avobenzone is a necessary but insufficient product requirement for achieving the highest proposed broad-spectrum classification, that is, critical wavelength of 370 nm or more. Although SPF and critical wavelength are largely independent of each other, UVA absorbance must increase commensurate with SPF to maintain the same critical wavelength value. Substrate spectrophotometry and the calculation of critical wavelength can readily account for sunscreen photostability by UV preirradiation. Finally there is also a strong positive relationship between critical wavelength and a currently available in vivo measure of UVA protection.

Conclusion: Determination of critical wavelength by means of UV substrate spectrophotometry provides a rapid, inexpensive, and reliable measure of broad-spectrum protection, which is largely independent of SPF, yet ensures long-wavelength UVA protection commensurate with SPE The procedure provides a routine, sensitive means of differentiating and classifying sunscreen products and, importantly obviates the need to subject volunteers to acute exposures of high-dose, nonterrestrial UV, the health risks of which are still poorly understood.

Abstract:
Background/Aim: The issue of the photostability of sunscreens has been frequently raised because of the possible loss of photoprotection, mainly in the UVA range, during sun exposure. Up to now, in vitro techniques have been mainly proposed to evaluate photostability. These techniques have generated controversial debates concerning the predictive value of these in vitro observations in relation to the in vivo reality during sun exposure.

 

Methods: Diffuse reflectance spectroscopy (DRS) is a recently developed technique that allows measurement of the UVA efficacy of sunscreen products in vivo on human volunteers. The absorption spectrum of the product is obtained by measuring the change in reflection of the skin with and without product. From this absorption spectrum, the UVA protective efficacy of the test product can be calculated for an appropriate source and a given biological action spectrum. We have used the DRS technique in vivo to determine the photostability of sunscreen products by measuring reflection spectra in the UVA range (320-400 nm) before and after product application and before and after UV exposure of the test products. Comparison between these spectra or between the corresponding calculated UVA protection factors has made it possible to determine the remaining level of protection in the UVA range after exposure. This study was designed to compare in vivo the protective efficiency and the photostability of three marketed sunscreen products (SPF 23-30) after solar-simulated exposure for SPF testing or after actual sun exposure. These in vivo data were then compared to in vitro photoinstability results.

Results: According to the in vitro measurements, one sunscreen product was found photostable and two products photo-unstable. After UVe exposure for in vivo SPF determination, a decrease in UVA absorption and UVA-PF was observed for the two photo-unstable products, while the photostable product did not present any decrease in UVA absorption. These results were confirmed through exposure to actual sun.

Conclusion: Our study confirms the prediction of the in vitro methods previously used to assess the photostability of sunscreen products. In addition, DRS provides a powerful new tool for the in vivo simultaneous evaluation of photostability and estimation of the UVA protection factor of sunscreen products performed during the test for SPF determination.

Abstract:
Background: Microfine zinc oxide (Z-Cote) is used as a transparent broad-spectrum sunblock to attenuate UV radiation (UVR), including UVA I (340-400 nm).

Objective: Our purpose was to assess the suitability of microfine zinc oxide as a broad-spectrum photoprotective agent by examining those properties generally considered important in sunscreens: attenuation spectrum, sun protection factor (SPF) contribution, photostability, and photoreactivity.

Methods: Attenuation spectrum was assessed by means of standard spectrophotometric methods. SPF contribution was evaluated according to Food and Drug Administration standards. Photostability was measured in vitro by assessing SPF before and after various doses of WR. Photoreactivity was evaluated by subjecting a microfine zinc oxide/organic sunscreen formulation to escalating doses of UVR and determining the percentage of organic sunscreen remaining.

Results: Microfine zinc oxide attenuates throughout the WR spectrum, including UVA I. It is photostable and does not react with organic sunscreens under irradiation.

Conclusion: Microfine zinc oxide is an effective and safe sunblock that provides broad-spectrum UV protection, including protection from long-wavelength UVA.

Abstract:
There is little dispute that modern suncare products should provide protection against exposure to both UVB and UVA radiation, and that the product should maintain this broad-spectrum protection throughout the period of exposure to the sun. We have described previously an in vitro methodology for the assessment of suncare product efficacy, by transmission spectroscopy. We now describe a modification to the method which takes into account the influence of the exposure of the product to solar UV by introducing pre-irradiation prior to the transmission measurements. By this means we can examine the influence of UV exposure on the protection efficacy of the product. UV pre-irradiation was achieved with a xenon are source optically filtered to achieve a spectrum simulating that of summer sunlight with a UV irradiance at the sample of 5 mW/cm(2). Different irradiation doses were applied to thin films of the suncare product, spread onto a UV transparent and chemically inert substrate. Spectral transmission was measured in both non-irradiated samples and samples irradiated with UV doses of 18, 36 and 54 J/cm(2), and sun protection factors (SPF) calculated. We found that the SPFs were only slightly modified when the active ingredients contained phostostable UV filters (e.g. butyl methoxydibenzoylmethane/4-methylbenzylidene camphor/terephthalylidene dicamphor sulfonic acid). However, with photo-unstable ingredients, the SPFs dropped significantly following UV exposure. For example, chemical filters containing butyl methoxibenzoylmethane/octyl methoxycinnamate suffered protection efficacy losses up to 50-60% of their initial value. The addition of photo-stabilizing UV filters did not prevent these reductions in protection efficacy. This study has demonstrated the importance of taking into account the photostability of suncare products when evaluating their protection efficacy by an in vitro technique. With sample pre-irradiation, it is possible to evaluate the efficacy of suncare products in more realistic experimental conditions akin to their use in vivo