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Photoprotection conferred by low level summer sunlight exposures against pro-inflammatory UVR insult

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Abstract

Tanning (melanisation and epidermal thickening) is a photoprotective response to solar UVR exposure, but it's unclear to what degree low-level exposures induce this in light-skin individuals, or whether this modifies the histological inflammatory response to UVR. Objectives were to examine if, in light-skin people, a simulated summer's casual sunlight exposures induces (i) melanogenesis, (ii) epidermal thickening and (iii) demonstrable protection against both clinical (erythema) and histological (neutrophil infiltration) impacts of higher-level, pro-inflammatory UVR challenge. A UVR intervention study was designed to simulate a summer's brief sunlight exposures (95% UVA, 5% UVB) as can provide sufficient vitamin D. Ten healthy adults of phototype II, median 47 years (range 30–59 years), 2 male/8 female, received 1.3 SED 3× weekly for 6 weeks, and were subsequently challenged with 2× personal MED of UVB on small areas of UVR-exposed and UVR-protected buttock skin. Skin erythema and pigmentation were measured spectrophotometrically. Punch biopsies were taken from (i) unexposed skin (ii) skin following the ×18 low-level UVR exposures and (iii) skin at 24 h following the 2 × MED challenge, with skin sections evaluated for epidermal thickness, and for neutrophil infiltration by immunohistochemistry. The 6-weeks’ UVR exposures significantly increased skin pigmentation, skin lightness (L*) reducing from 69.37 (SD 2.8) to 65.52 (2.33) at course-end (p < 0.001), and stratum corneum thickness rising from 29.3 (9.59) to 41.5 (12.7)μm (p < 0.05); there was no influence on neutrophil numbers. Following the pro-inflammatory (2× MED) UVR challenge, there was a small (18%) reduction in erythema but a proportionately greater (71%) reduction in neutrophil infiltration in skin prior-exposed to the UVR course compared with photoprotected skin (both p < 0.05). Thus, findings add to information on risk-benefit of low-level sunlight exposure. Even very light-skin people show measurable although modest photoprotective responses to repeated low-dose UVR; greater impact is seen on histological than clinical inflammation.

Graphical abstract: Photoprotection conferred by low level summer sunlight exposures against pro-inflammatory UVR insult

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Article information


Submitted
19 Nov 2019
Accepted
31 Mar 2020
First published
19 May 2020

This article is Open Access

Photochem. Photobiol. Sci., 2020, Advance Article
Article type
Paper

Photoprotection conferred by low level summer sunlight exposures against pro-inflammatory UVR insult

S. J. Felton, B. B. Shih, R. E. B. Watson, R. Kift, A. R. Webb and L. E. Rhodes, Photochem. Photobiol. Sci., 2020, Advance Article , DOI: 10.1039/C9PP00452A

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