Light therapy using UltraViolet B rays (UVB) has been known to be beneficial. UVB is used by physicians in prescription light boxes. It is not the same as the UVA light used at tanning salons. The difference between UVB and UVA is the length of the light wave.

UVA is the light used in PUVA therapy in combination with psoralen. A medication is administered, either orally, topically, or the patient is soaked in a diluted solution of the medication prior to exposure to the light therapy. This increases photosensitivity.

A physician should monitor both types of light therapy. In some parts of the world, total exposure is monitored to reduce the risk of skin cancer.

Current thinking is that UVA light therapy used in combination with a psoralen (an oral medication) is the preferred method (PUVA). The UV dosage is administered in the doctor's office and carefully monitored for the amount of exposure. There is a limit on the total exposure time that can be administered. Protective glasses must be worn to reduce the risk of cataracts, and skin cancer is a potential risk. The psoriasis tends to return when discontinued. The cost: $30 to $50 per session. Patients may need 3 to 5 sessions per week.

There are some questions about long term use of UV therapy and the possibility of increasing the users potential of skin cancer.