Harvard Men's Health Watch

Psoriasis: More than skin deep

The first accurate medical discussion of psoriasis dates back to 1801, but the disease itself is much older. In fact, its very name is borrowed from an ancient Greek word meaning an itchy or scaly condition. About 7 million Americans are plagued by this itching and scaling, and many of them have serious complications involving other organs. Although psoriasis is classified as a dermatologic disease, it doesn't start in the skin, and its damage may be more than skin deep.

Beneath it all

At a basic level, psoriasis is a disorder of the immune system. White blood cells called T-helper lymphocytes become overactive, producing excess amounts of cytokines, such as tumor necrosis factor, interleukin-2, and interferon-gamma. In turn, these chemicals trigger inflammation in the skin and other organs. In the skin, the inflammation produces three characteristic findings: widened blood vessels, accumulation of white blood cells, and abnormally rapid multiplication of keratinocytes, the main cells in the outer layer of the skin. In healthy skin, keratinocytes take about a month to divide, mature, migrate to the skin surface, and slough off to make way for younger cells. But in psoriasis, the entire process is speeded up to as little as three to five days. The result is thickened, red skin that sheds silvery scales of keratinocytes that have matured before their time (see Figure 1).

Figure 1: Psoriasis

illustration of cross section of normal skin and skin with psoriasis

In contrast with normal skin (left), people with psoriasis develop characteristic scaly, red patches when new skin cells are produced at a more rapid rate and do not mature normally. Inflammation and the growth of new blood vessels redden the affected areas.

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