Normally, the cells of the outer layer of the skin are constantly shed and replaced by new cells. In psoriasis, for reasons medical science has yet to determine, something occurs to speed up the rate of production of new skin cells, which then accumulate in thick, lumpy, reddish, flaky patches on the surface of the skin. Some people are constantly bothered by lesions on one or another part of their bodies. Others, with milder forms of psoriasis may have only a few patches from time to time.
An outbreak may be triggered by any once of a number things: any injury to the skin may be followed by psoriasis in that area; a burn or cut, severe sunburn, allergies or throat infections may also cause an attack.
Psoriasis seems to be inherited and can appear at any age. Fortunately, the condition is not contagious. The scaly patches of skin produced by psoriasis can often be made to disappear through treatment with an ultraviolet lamp or sunbathing. There are also a variety of ointments, creams, pastes patches to reduce scaling and relieve discomfort; special bath additives and shampoos may also be used. Some of these contain coal tar, which makes the skin more sensitive to light. Tar and ultraviolet light treatment have been extremely effective in reducing psoriasis in some people, and so have topical preparations containing the chemical dithranol. Sometimes psoriasis is treated with a combination of a medication called psoralen and ultraviolet light; this is known as PUVA therapy. Topical steroids may be helpful, but they can create side effects if overused.
A new medication, etretinate, is available for use by dermatologists in severe cases, but because it is a long-acting vitamin A derivative, women of childbearing age should be given advice on avoiding pregnancy while using it and for at least a year after discontinuation. The anticancer drug methotrexate, which slows the rate at which cells divide, can also be used for severe and disabling cases. It too can have serious side effects, so it is reserved for cases where other treatment has not been successful.