Synergistic effects of long-wavelength ultraviolet A1 and visible light on pigmentation and erythema
Kohli I, Chaowattanapanit S, Mohammad TF, Nicholson CL, Fatima S, Jacobsen G, Kollias N, Lim HW, Hamzavi I. Synergistic effects of long-wavelength ultraviolet A1 and visible light on pigmentation and erythema. J Am Acad Dermatol 2018; 79(3):AB277.
J Am Acad Dermatol
Background: Visible light (VL) induces multiple cutaneous effects including dark and persistent pigmentation in addition to erythema, thermal damage, and free radical production. Sunscreen testing protocols recommended by regulatory bodies throughout the world require the use of solar simulators with spectral output in ultraviolet (UV) domain only. However, sunlight contains VL and infrared radiation also.
Objective: This study aimed to evaluate the contributions of VL and UVA1 on pigmentation and erythema, and optimize parameters for in vivo testing.
Methods: Ten subjects with Fitzpatrick skin phototype IV-VI were enrolled. Subjects were irradiated on their back with VL using 2 light sources: 1 containing pure VL and 1 containing VL with <0.5% UVA1 (VL+UVA1). Four different irradiances were administered to investigate reciprocity behavior which states that a response is directly proportional to the dose, a product of irradiance and exposure time, and independent from the individual values of the 2. Assessments, including photography, investigator’s global assessment, colorimetry, and spectroscopy, were performed immediately, 24 hours, 7 days, and 14 days after irradiation.
Results: Pigmentation was observed with both light sources; however, pigment intensity was greater with VL+UVA1 than pure VL. Reciprocity was observed in pure VL sites, but not VL+UVA1. Variation in spectral output had greater impact on pigment intensity than irradiance. Clinical erythema was observed on the VL+UVA1 side, but not on the pure VL side. Protocol for testing photoprotection product efficacy against VL induced effects has been proposed.
Conclusions: The findings suggest a synergistic relationship between VL and UVA1 and emphasize the need for developing means of photoprotection against VL.