Psoriasis

Alternative names:

plaque psoriasis

Definition:

A common inflammatory skin condition characterized by frequent episodes of redness, itching, and thick, dry, silvery scales on the skin.

Causes, incidence, and risk factors:

Psoriasis is very common, with approximately 3 million Americans affected (or about 8 out of 10,000 people). It can appear suddenly or gradually. It may affect any age but most commonly begins between 15 to 35 years old. It occurs most frequently in Caucasians. Psoriasis is characterized by frequent episodes of recurrences and remissions.

Psoriasis seems to be an inherited disorder, and it appears to be related to the immune or inflammatory response. It is most commonly seen on the trunk, elbows, knees, scalp, skin folds, or fingernails, but it may affect any or all parts of the skin. Normally, skin takes about a month for its new cells to move from the lower layers of skin up to the surface. In psoriasis, this process takes only a few days, resulting in build-up of dead skin cells and formation of thick scales.

Psoriasis may be aggravated by injury or irritation (cuts, burns, rash, insect bites), and it may be severe in immunosuppressed people (such as with chemotherapy for cancer, or with AIDS) or those who have autoimmune disorders (rheumatoid arthritis). Medications, viral or bacterial infections, excessive alcohol consumption, obesity, lack of sunlight, overexposure to sunlight (sunburn), stress, general poor health, cold climate, and frequent friction on the skin are also associated with flare-ups of psoriasis. Psoriasis is not contagious.