skin disorders
Psoriasis
Phototherapy
Phototherapy (exposure to ultraviolet light) also can help clear up psoriasis for several months at a time (see sidebar). Phototherapy is often used in combination with various topical medications, particularly when large areas of skin are involved, but it is not being used as much because other effective medications are available. Traditionally, treatment has been with phototherapy combined with the use of psoralens (medications that make the skin more sensitive to the effects of ultraviolet light). This treatment is called PUVA (psoralen plus ultraviolet A). Many doctors are now using narrowband ultraviolet B (NBUVB) treatments, which are as effective as PUVA. However, NBUVB treatments are done without psoralens and therefore do not have the same side effects, such as extreme sensitivity to sunlight. Doctors can also treat specific patches of the skin directly by using a laser that focuses ultraviolet light (called excimer laser therapy). Exposure to sunlight is helpful for certain skin disorders. One component of sunlight―ultraviolet (UV) light―is responsible for this effect. UV light has many different effects on skin cells, including altering the amounts and kinds of chemicals they make and causing the death of certain cells that can be involved in skin diseases. The use of UV light to treat disease is called phototherapy. Psoriasis and Because exposure to natural sunlight varies in intensity and is not practical for a large part of the year in certain climates, phototherapy is nearly always done with artificial UV light. Treatments are given in a doctor's office or in a specialized treatment center. UV light, which is invisible to the human eye, is classified as A, B, or C, depending on its wavelength. Ultraviolet A (UVA) penetrates deeper into the skin than ultraviolet B (UVB). UVA or UVB is chosen based on the type and severity of the person's disorder. Ultraviolet C is not used in phototherapy. Some lights produce only certain specific wavelengths of UVA or UVB (narrowband therapy), which are used to treat specific disorders. Narrowband therapy helps limit the sunburn–like effect caused by phototherapy. Phototherapy is sometimes combined with the use of a psoralen. The combination of a psoralen plus UVA is known as PUVA therapy. Psoralens are medications that may be taken by mouth before treatment with UV light. Psoralens sensitize the skin to the effects of UV light, allowing shorter, less intense exposure. Side effects of phototherapy include pain and reddening similar to sunburn with prolonged exposure to UV light. UV light exposure also increases the long-term risk of skin cancer, but the risk is small for brief courses of treatment. Psoralens often cause nausea and extreme sensitivity to sunlight. In addition, because psoralens enter the lens of the eye, UV-resistant sunglasses must be worn for at least 12 hours after undergoing PUVA therapy. 