617 The impact of the spectral composition of long-wavelength ultraviolet A1 and visible light on cutaneous biologic effects

Background & Aim: Recent studies have demonstrated visible light and long-wavelength UVA1 (VL+UVA1, 370-700 nm) to cause erythema in light skin and synergistically increased pigmentation in dark skin subjects.1, 2 Spectral compositions of VL+UVA1 may further impact these biologic effects. Yet, no phototesting guidelines exist, thus hindering the development of reliable sunscreens protective against this part of sunlight. The objective of this study was to optimize the spectral output of VL+UVA1 as a step to standardize the assessment of protection from VL+UVA1. Methods: Four subjects with Fitzpatrick skin phototype (SPT) I-III were enrolled in this prospective pilot study. Two VL+UVA1 light sources were used: one with 2% UVA1 and another with 4% UVA1. to match more closely that measured in sunlight. Subjects were irradiated with each light source at 320 J/cm2. Clinical scoring, diffuse reflectance spectroscopy (DRS), and colorimetry were performed immediately, 24 hours, 7 days, and 14 days after irradiation. Results: In all subjects, irradiation with VL+ 4% UVA1 resulted in a stronger cutaneous response than that with VL+ 2% UVA1, showing an average 4-fold and 3-fold increase in immediate erythema and delayed pigmentation, respectively. These results were supported by colorimetry measured Δ a*, Δ ITA, and DRS measured relative dyschromia. Conclusion: These preliminary results indicate that the spectral composition of VL+UVA1 impact cutaneous responses and an output resembling sunlight should be strongly considered when standardizing sunscreen phototesting guidelines. This will enable a realistic and standardized design for the evaluation of sunscreen photoprotection within this spectrum