Background: National sun protection guidelines currently assume exposure to low-intensity sunlight (UV Index <3) is not harmful. However, this is not well supported by evidence. This experimental study investigates the molecular and immunologic effects of low-dose and low-intensity ultraviolet radiation (UVR) on human skin with the aim of generating evidence to determine safe sun exposure thresholds.
Methods: We exposed a small area of skin on participants’ lower back to suberythemal doses (0.7 SED and 1.6 SED) of solar-simulated ultraviolet (ssUVR) across four consecutive days. Doses were delivered at either UVI 2.8 or UVI 8.0. Skin biopsies were collected at baseline, and from exposed sites on day 1 post-ssUVR (to assess immediate effects), at 24 hours (to assess intermediate effects), and at day 4 (to assess cumulative effects). Immunohistochemistry staining was used to assess induction of p53 and cyclobutane pyrimidine dimers (CPD) damage in epidermal cells.
Results: A pre-planned interim analysis on the first 30 participants found increases in p53 and CPD staining by day 4 after both 0.7 and 1.6 SED. The intensity at which the ssUVR was delivered appeared to influence levels of CPD but not p53. We plan to recruit more participants to more precisely estimate the effects of exposing skin to low-intensity ssUVR.
Discussion: Preliminary results suggest DNA damage is induced in epidermal cells, even when the UV Index is below 3. Pending further evidence, this study is expected to provide mechanistic data needed to address the key evidence gap in current Australian sun protection policies.