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Photostability of commercial sunscreens upon sun exposure and irradiation by ultraviolet lamps

Journal article
Authors Helena Gonzalez
Nils Tarras-Wahlberg
Birgitta Strömdahl
A Juzeniene
J. Moan
Olle Larkö
Arne Rosen
Ann-Marie Wennberg
Published in BMC Dermatol
Volume 7
Pages 1
ISSN 1471-5945
Publication year 2007
Published at Department of Physics (GU)
Institute of Clinical Sciences
Pages 1
Language en
Links dx.doi.org/10.1186/1471-5945-7-1
Keywords Area Under Curve, Drug Stability, Spectrophotometry, *Sunlight, Sunscreening Agents/*chemistry, Ultraviolet Rays
Subject categories Dermatology and Venereal Diseases

Abstract

BACKGROUND: Sunscreens are being widely used to reduce exposure to harmful ultraviolet (UV) radiation. The fact that some sunscreens are photounstable has been known for many years. Since the UV-absorbing ingredients of sunscreens may be photounstable, especially in the long wavelength region, it is of great interest to determine their degradation during exposure to UV radiation. Our aim was to investigate the photostability of seven commercial sunscreen products after natural UV exposure (UVnat) and artificial UV exposure (UVart). METHODS: Seven commercial sunscreens were studied with absorption spectroscopy. Sunscreen product, 0.5 mg/cm2, was placed between plates of silica. The area under the curve (AUC) in the spectrum was calculated for UVA (320-400 nm), UVA1 (340-400 nm), UVA2 (320-340 nm) and UVB (290-320 nm) before (AUCbefore) and after (AUCafter) UVart (980 kJ/m2 UVA and 12 kJ/m2 of UVB) and before and after UVnat. If theAUC Index (AUCI), defined as AUCI = AUCafter/AUCbefore, was > 0.80, the sunscreen was considered photostable. RESULTS: Three sunscreens were unstable after 90 min of UVnat; in the UVA range the AUCI was between 0.41 and 0.76. In the UVB range one of these sunscreens was unstable with an AUCI of 0.75 after 90 min. Three sunscreens were photostable after 120 min of UVnat; in the UVA range the AUCI was between 0.85 and 0.99 and in the UVB range between 0.92 and 1.0. One sunscreen showed in the UVA range an AUCI of 0.87 after UVnat but an AUCI of 0.72 after UVart. Five of the sunscreens were stable in the UVB region. CONCLUSION: The present study shows that several sunscreens are photounstable in the UVA range after UVnat and UVart. There is a need for a standardized method to measure photostability, and the photostability should be marked on the sunscreen product.

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