Studies investigating the effect of UV radiation on acne have demonstrated a modest improvement in only inflammatory acne. There is some effect with UVB radiation alone, and slightly more benefit with combined UVB and UVA radiation. UVA light alone is the least beneficial. Twice-weekly phototherapy sessions are needed for clinical improvement. The therapeutic utility of UV radiation in acne is superseded by its carcinogenic potential (116-120).
Visible light is effective in treating both inflammatory and non-inflammatory acne lesions (121). A high-intensity, enhanced, narrow band (407-420 nm) blue-light source (ClearLight) has been FDA-approved for the treatment of moderate inflammatory acne (122). Red light can also be used to treat acne. It is less effective at photoactivating porphyrins than blue light, but red light can penetrate deeper into the dermis. Red light may also have additional anti-inflammatory properties. Combined blue and red light therapy may be more efficacious than either alone. It can be used twice weekly, taking 15 minutes per session to treat just the face. To treat the face, chest, and back, a 45-minute session is needed. Clinical improvement is maintained for at least one month after the last treatment (121).