Phototherapy uses two types of ultraviolet (UV) light to destroy cancer cells: ultraviolet A (UVA) or ultraviolet B (UVB). Both types of UV light are administered using fluorescent lamps specially calibrated to maximize the effect of treatment while minimizing the risk of burns. Phototherapy treatments are usually given twice a week for UVA and three times a week for UVB. If UVA light is used, the patient is first given drugs called psoralens. The combination of UVA light and psoralens is called PUVA. Approximately two hours before treatment, the patient takes psoralens orally as a pill. This allows the drugs time to circulate throughout the body. The UVA light activates the drugs, destroying the cells the drugs came into contact with. Psoralens can cause nausea in some patients. Treatment with PUVA can cause increased sensitivity to sunlight. This can increase a person’s risk of severe skin burns and cataracts. For this reason, it is very important for patients treated with PUVA to take measures to protect themselves from the sun in the two days immediately following treatment. This type of treatment can also increase a person’s risk of developing skin cancer in the future, so a patient’s total number of light treatments is limited to a predetermined maximum number of sessions. UVB light is typically used to treat thinner skin lesions. Treatment with UVB light does not require additional drugs.