Antioxidants add protection to a broad-spectrum sunscreen

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Abstract
Background. Exposure of human skin to ultraviolet radiation (UVR) results in erythema, pigment darkening, skin cancer and photoageing. In addition to conventional organochemical and the physical–mineral type sunscreens (SS), other non‐SS protective strategies have been investigated, including antioxidants (AOx) and topical DNA repair enzymes. Aim. To investigate whether AOx could improve the protection provided by a broad‐spectrum sunscreen (SS) preparation. Methods. Volunteers were exposed to repetitive solar‐simulated (ss)UVR at 1.5 times minimal erythema dose for four consecutive days. Thirty minutes before each exposure and 6, 24 and 48 h after the last exposure, the test materials [vehicle, SS (sun protection factor 25) alone, AOx alone and SS plus AOx] were applied to four different sites. Another two sites received ssUVR only, or SS plus AOx only, and a third site was left untreated (neither ssUVR or product). Erythema and pigmentation were measured using a Mexameter. Biopsy specimens were taken 72 h after the last irradiation. The thickness of the stratum corneum and epidermis were measured by microscopy. Expression of cytokeratins (CKs), matrix metalloproteinases (MMPs) and CD1a‐positive Langerhans cells (LCs) analysed by immunohistochemical staining, and relative expression levels were compared between all seven sites. Results. AOx alone did not reduce erythema. There was a significant reduction in pigmentation, and the product almost completely protected against LC depletion. AOx plus SS gave better protection against pigment formation and CK5/6 induction than SS alone. AOx alone protected against ssUVR‐induced hyperproliferation, as shown by epidermal thickness and CK16 biomarkers, and was better than SS alone. Interestingly, although protection against induction of MMP‐9, a marker of photoageing, did not reach significance when either SS or AOx were applied separately, there was complete protection against MMP‐9 induction when these were combined. Conclusions. Non‐SS materials such as AOx can contribute significantly to sun protection when added to a broad‐spectrum SS and applied topically to human skin in vivo.

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