Cancer-preventive effects of sunscreens are uncertain
ABSTRACT Provocative findings have been published suggesting that the use of sunscreens may promote skin cancer. A recent meeting of international experts on the use of sunscreens and skin cancer was held at the International Agency for Research on Cancer in Lyon. The workshop concluded that the topical use of sunscreens reduces the risk of sunburn and that sunscreens probably prevent squamous-cell carcinoma of the skin when used mainly during unintentional sun exposure. No conclusion could be drawn about the cancer-preventive activity of topical sunscreens against basal-cell carcinoma and cutaneous melanoma. The use of sunscreens can extend the duration of intentional sun exposure, such as sunbathing. Such an extension may increase the risk for cutaneous melanoma. The workshop warned against relying solely on sunscreens for protection from ultraviolet radiation.
- SourceAvailable from: Riccardo Castagna
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- "To achieve greater protection against the damaging effects induced in skin by UVA, the majority of daily skin care cosmetic products now contain UV absorbers  . However, although sunscreens are useful because they efficiently protect skin against erythema and edema and probably prevent squamous cell carcinoma    , they also seem to provide much less protection than expected    . In fact, the Sun Protection Factor (SPF) reported on sunscreens, which is a measure of their biological activity (prevention of erythema), may significantly change due to several reasons such as de-emulsification and absorption of the sunscreen when applied to a substrate . "
ABSTRACT: Owing to the spectral distribution of solar UV, the UVA component of sunlight is now believed to be the main cause of photoaging and photocarcinogenesis and is much more effective than UVB in inducing peroxidative damage. Consequently, most skin care cosmetic products now include UVA filters in their formulations along with UVB filters. These modern sunscreens should provide and maintain their initial absorbance, hence protection, throughout the entire period of exposure to sunlight. However, not all UVA and UVB filters are sufficiently photostable. In this study, we examine the correlation between the photochemical degradation of sunscreen agents under UVA irradiation, with particular reference to the UVA-absorber 4-tert-butyl-4'-methoxydibenzoylmethane, alone and in combination with other organic UV filters (2-ethylhexyl 4 methoxycinnamate and 2-ethylhexyl 2-cyano-3,3-diphenylacrylate) and their ability to prevent UVA-induced lipid peroxidation. Since antioxidants are also added to formulations to deactivate free radicals generated during UVA exposure, vitamin E and the synthetic antioxidant, bis(2,2,6,6-tetramethyl-1-oxyl-piperidine-4-yl)sebacate, a nitroxide derivative, were also included in this study. By using simple in vitro tests, the results show that a decrease in spectral absorbance of the UV filters correlates in most cases with increased UVA-induced lipid peroxidation; this depends on the specific UV absorber analysed and also on whether they are alone or in combination. Furthermore, the combined presence or absence of antioxidants has a profound effect on this oxidative event. In particular, the nitroxide appears to be a more efficient photo-antioxidant than vitamin E. Similar experiments were also performed under natural sunlight and the results obtained did not differ substantially from those performed under UVA. The results presented and discussed in this work may help in understanding the effects of UVA/UVB absorbers and antioxidants upon the level of UV-induced ROS generated under UVA exposure and in natural sunlight which could be relevant for improving the photoprotection and efficacy of skin care cosmetic formulations.Journal of Photochemistry and Photobiology B Biology 04/2006; 82(3):204-13. DOI:10.1016/j.jphotobiol.2005.03.011 · 2.80 Impact Factor
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- "Sunscreen use has been shown to decrease the formation of actinic keratoses, which are linked to squamous cell carcinomas (Thompson et al, 1993; Naylor et al, 1995). Animal models have shown that sunscreens reduce the incidence of basal and squamous cell tumors (Sekura Snyder and May, 1975; Kligman et al, 1980; Forbes et al, 1989; Reeve et al, 1990), which are UVB related; however, there have been several studies to suggest that sunscreen use is associated with increased risk of melanoma (Autier et al, 1995; Azizi et al, 2000; Vainio and Bianchini, 2000). This may re£ect inadequate sunscreen application (Stokes and Di¡ey, 1997; Wulf et al, 1997; Reprint requests to: Rachel Haywood, RAFT Institute of Plastic Surgery, Mount Vernon Hospital, Northwood, Middlesex, HA6 2RN, UK. "
ABSTRACT: Sunscreens are employed to mitigate the adverse effects of sunlight on skin but are primarily designed to prevent ultraviolet-B-associated burning and damage. The increasingly recognized role of ultraviolet A in aging, and possibly melanoma, highlights the need to include ultraviolet A screens; however, validation remains difficult. We have used a novel method to establish the efficacy of sunscreens, by measuring ultraviolet-A-induced free-radical production (thought to contribute towards ultraviolet-A-related aging and malignant change). Electron spin resonance spectroscopy was used to detect free radicals directly in human Caucasian skin during irradiation with levels of ultraviolet comparable to solar intensities. Using this system the protection afforded by three high factor sunscreens (sun protection factor 20+) that claim ultraviolet A protection was examined. Each sunscreen behaved similarly: at recommended application levels (> or = 2 mg per cm2) the ultraviolet-induced free radicals were reduced by only about 55%, and by about 45% at 0.5-1.5 mg per cm (0.5 mg per cm2 reported for common usage). A "free-radical protection factor" calculated on the basis of these results was only 2 at the recommended application level, which contrasts strongly with the erythema-based sun protection factors (mainly indicative of ultraviolet B protection) quoted by the manufacturers (20+). The disparity between these protection factors suggests that prolonged sunbathing (encouraged by use of these creams) would disproportionately increase exposure to ultraviolet A and consequently the risk of ultraviolet-A-related skin damage.Journal of Investigative Dermatology 11/2003; 121(4):862-8. DOI:10.1046/j.1523-1747.2003.12498.x · 6.37 Impact Factor
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ABSTRACT: To investigate the association between theoretically grounded psychosocial motivators and the sun safety practice intentions of rural youth. A survey was given to 219 members of FFA (Future Farmers of America) at high schools in the rural Midwest (average age = 16). Perceived self-efficacy, peer norms, response efficacy, and susceptibility predicted protective clothing and sunscreen use intentions. Among boys, perceived norms among same-sex peers; but among girls, norms among both same- and opposite-sex peers, were significant. Self-efficacy should be an important component of sun safety education for rural youth. Gender-specific peer norms should also be addressed.American journal of health behavior 01/2010; 34(4):412-9. DOI:10.5993/AJHB.34.4.3 · 1.31 Impact Factor