Phototherapy is the use of specific wavelengths of light shone directly on affected areas of skin. This light occurs naturally as a component of sunlight and is part of the ultraviolet light spectrum.
Phototherapy treats psoriasis by slowing abnormal growth of normal skin cells, preventing flare ups. Phototherapy treats vitiligo by stimulating the production of melanocytes, resulting in repigmentation. Different wavelengths of light on the UV spectrum are used, driven by the condition that needs to be treated.
This depends on your condition. A common treatment protocol is exposing skin to phototherapy lights 3 times per week, with sessions starting with a few seconds and increasing to several minutes over time. Once skin is clear, your doctor will determine whether maintenance requires regular phototherapy or whether your remission needs only periodic checkups.