Skin Erythema and Blood Flow Responses to Acute Ultraviolet Radiation Exposure

Acute exposure to ultraviolet (UV)‐B light elicits an inflammatory response in the skin, resulting in erythema (reddening) and increased skin blood flow over the following 24 hours. However, the time course of, and relation between, these responses is unclear. Likewise, it is unknown whether these responses differ following exposure to broad spectrum (UV‐AB) vs. UV‐B light, as well as how application of sunscreen on the skin impacts these two responses. Purpose To examine (1) the time course of erythema and skin blood flow responses over 8 h following acute UV‐B and UV‐AB exposure, and (2) the impact of sunscreen application on those responses. We hypothesized that (1) the erythema and blood flow responses would track each other, (2) both responses would be higher following UV‐AB compared to UV‐B exposure, and (3) sunscreen would attenuate responses to both UV‐AB and UV‐B. Methods The ventral aspect of both forearms of 10 healthy young adults (25±4 yrs; 6M/4F) were exposed to either UV‐AB (10 mJ/cm 2 ; 6 mJ/cm 2 UVA + 4 mJ/cm 2 UV‐B) or UV‐B (4 mJ/cm 2 ). Two 2‐cm 2 sites on each arm were randomly chosen for acute UV exposure with or without pre‐treatment with topical SPF‐50 sunscreen. Erythema index (EI; reflectance spectrometry) and red cell flux (laser‐Doppler flowmetry) were measured at each site before, immediately after, and 2, 4, 6, and 8 h post‐exposure. Cutaneous vascular conductance was calculated (CVC=flux/MAP) at each time point and both EI and CVC were expressed as change from baseline. Results EI increased linearly after exposure to UV‐B (p<0.01 at 4, 6, and 8 h post‐exposure) and UV‐AB (p=0.02 at 6 h, p<0.01 at 8 h). Unlike the immediate increase in EI, no increase was seen for CVC until 4 h post‐UV‐B (p<0.01) and UV‐AB (p=0.06). Sunscreen effectively blocked the EI response to both UV‐B and UV‐AB exposures (p>0.05) and prevented, the CVC responses to UV‐B (p<0.01 at 6 and 8 hours) and UV‐AB (p=0.03 at 8 h). Conclusion Exposure to UV‐B or UV‐AB induced an immediate and linear increase in EI, but a delayed (by 4 h) increase in CVC. Sunscreen prevented the EI response and blunted the rise in CVC. These data suggest that the inflammatory response to acute UV exposure is characterized by an immediate erythema response and a delayed blood flow response in the cutaneous microvasculature and that sunscreen may protect against both responses. Support or Funding Information ACSM Foundation Doctoral Student Research Grant This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .