Sunscreens Inadequately Protect Against Ultraviolet-A-Induced Free Radicals in Skin: Implications for Skin Aging and Melanoma?
Open accessAbstract
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.
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A recent study of three high SPF broad-screen sunscreens revealed that at 2 mg per cm2 application, UVA-induced free radical formation was reduced only 55% with even worse protection when application levels were decreased.
“Indeed a recent study of three high SPF broad-screen sunscreens revealed that at 2 mg per cm 2 application, UVAinduced free radical formation was reduced only 55% with even worse protection when application levels were decreased (Haywood et al, 2003).”
From Ferulic Acid Stabilizes a Solution of Vitamins C and E and Doubles its Photoprotection of Skin (2005) · cites this paper as Haywood et al, 2003
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“5mg/cm(2)) simulating the average amount applied by consumers reduced free radical production by 46% [55].”
Background
- Authors
- Haywood, R., Wardman, P., Sanders, R., & Linge, C.
- Affiliations
- Mount Vernon Hospital (GB)
- Corresponding author
- Haywood, Rachel
- ORCID
- Wardman, Peter
- Venue
- Journal of Investigative Dermatology
- Publisher
- Elsevier BV
- Published
- 2003-10
- Volume
- 121
- Issue
- 4
- Pages
- 862-868
- ISSN
- 0022-202X (ISSN-L)
- OpenAlex
- W2030827853
- Cited by
- 162
- References
- 1
- Citations by year
- 2026: 4 · 2025: 3 · 2024: 4 · 2023: 5 · 2022: 4 · 2021: 4 · 2020: 7 · 2019: 11 · 2018: 3 · 2017: 9 · 2016: 10 · 2015: 5 · 2014: 9 · 2013: 4 · 2012: 8
- FWCI
- 9.23
- Type
- journal article
- Language
- en
- Open access
- bronze
- doi.org
- Licence
- Locations
- Journal of Investigative Dermatology (publishedVersion)
- PubMed (publishedVersion)
- Funders
- Cancer Research UK
- Topics
- Health Sciences › Medicine › Dermatology › Skin Protection and Aging
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Cell Biology › melanin and skin pigmentation
- Health Sciences › Medicine › Epidemiology › Nonmelanoma Skin Cancer Studies
- Keywords
- sunscreen, UVA, free radicals, skin aging, melanoma, sun protection factor, sunscreen efficacy, human skin, sunbathing, ultraviolet radiation
- MeSH terms
- Free Radicals, Humans, Melanoma, Skin, Skin Neoplasms, Sunscreening Agents, Ultraviolet Rays, Reproducibility of Results, Skin Aging, Oxidative Stress, In Vitro Techniques
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