Phototherapy Narrow band ultraviolet light (UVB) is most commonly used to treat psoriasis but can also be used for eczema, acne, vitiligo, mycosis fungoides and a variety of other skin diseases. It is commonly referred to as phototherapy. The narrow band of UVB that this medical light therapy emits is a specific safe range that does not cause the redness, burning nor the skin cancer risks, that lower UVB bands emit. It is safe for pregnant women and children. Phototherapy often avoids the needs to medications and thus their side effects.