The most common type of phototherapy used to treat skin diseases is narrowband UVB. UV radiation with a wavelength between 311 and 312 nm is called a narrowband. It used to be that UVB phototherapy was provided through a broad-spectrum source (290 to 320 nm).

A skin condition caused by an overreaction of the immune system can be treated with it. Among the skin conditions that can be treated with phototherapy are: Psoriasis – a condition where the skin develops red, silvery, scaly patches. The ailment of eczema is characterized by itchy and red skin, or by allergic dermatitis.