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Phototherapy is the controlled medical exposure to sunlight or artificially produced ultraviolet radiation. Measured doses of specific ultraviolet (UV) wavelengths are used to treat many skin conditions (e.g., pruritus, atopic dermatitis). However, this therapy is not for everyone. It is not typically recommended for children or patients with sun allergies or conditions that worsen when exposed to sunlight.

Phototherapy works by a variety of mechanisms, including:

• Reducing DNA synthesis, which reduces accelerated cell growth, such as that caused by cells in the epidermis affected by psoriasis.
  
  

  

• Inducing release of certain hormones (prostaglandin) and proteins (cytokines) that cause light reactions (e.g., increased pigmentation, sunburn).
  
  
• Suppressing the immune system, which reduces the exaggerated immune response of contact allergies and hypersensitivity.

Topical agents and combination therapies are often used in combination with phototherapy. The goal of this is to minimize the risk of long-term side effects, increase the effectiveness of each treatment and reduce the doses of ultraviolet light required.