What is the difference between phototherapy and tanning session?

Phototherapy. Uv phototherapy is the use of ultraviolet light, prescribed by a physician, for the treatment of skin disorders such as vitiligo, eczema and psoriasis. The treatment may consist of ultraviolet in the uva, narrow-band uvb, or broadband uvb wave ranges. Most medical phototherapy is narrow-band uvb and salon tanning beds are uva.