Phototherapy, also known as light therapy, uses specific wavelengths of ultraviolet (UV) light to treat skin disorders. In the case of phototherapy for scalp psoriasis, narrowband UVB (NB-UVB) is the most commonly used type. This light penetrates the skin and helps reduce the hyperactive immune response that causes rapid skin cell growth.

Because of the hair barrier, scalp treatments often require specialized devices such as handheld UV combs or targeted laser systems. These tools part the hair and deliver light directly to the scalp, making treatment more efficient and less invasive.