TY - JOUR

T1 - Photoprotection conferred by low level summer sunlight exposures against pro-inflammatory UVR insult

AU - Felton, S.J.

AU - Shih, B.B.

AU - Watson, R.E.B.

AU - Kift, R.

AU - Webb, A.R.

AU - Rhodes, L.E.

PY - 2020/6/1

Y1 - 2020/6/1

N2 - 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.

AB - 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.

U2 - 10.1039/c9pp00452a

DO - 10.1039/c9pp00452a

M3 - Journal article

VL - 19

SP - 810

EP - 818

JO - Photochemical and Photobiological Sciences

JF - Photochemical and Photobiological Sciences

SN - 1474-905X

IS - 6

ER -