Psoriasis

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Psoriasis on the knuckles

Psoriasis is a common skin inflammation (irritation and swelling) characterized by frequent episodes of redness, itching, and thick, dry, silvery scales on the skin.

Plaque psoriasis

Psoriasis is a very common condition, with approximately 5 million Americans affected. It can appear suddenly or gradually. In many cases, psoriasis goes away and then flares up again repeatedly over time. The disorder may affect people of any age, but it most commonly begins between ages 15 and 35.

Psoriasis seems to be an inherited disorder, probably related to an inflammatory response in which the immune system accidentally targets the body's own cells. Evidence of the condition is most commonly seen on the trunk, elbows, knees, scalp, nails, trunk, or less commonly, skin folds, but it may affect any or all parts of the skin.

Normally, it takes about a month for new skin cells to move up from the lower layers to the surface. In psoriasis, this process takes only a few days, resulting in a build-up of dead skin cells and formation of thick scales.

Psoriasis may be aggravated by injury or irritation (such as cuts, burns, rashes, insect bites). It may be severe in immunosuppressed people (like those with AIDS or undergoing chemotherapy for cancer), or those who have other autoimmune disorders (such as rheumatoid arthritis). Up to 30% of people with psoriasis may also have arthritis, a condition known as psoriatic arthritis.

Some medications (notably beta blockers and lithium), viral or bacterial infections (most commonly strep), excessive alcohol consumption, friction, sunburn, conditions of dryness or low sunlight such as occur in the winter, and stress can also cause psoriasis flare-ups or make psoriasis more difficult to treat. The condition is not contagious.

Infections with strep may cause the sudden appearance of numerous, small lesions of psoriasis, in a pattern that resembles raindrops. This condition is called guttate psoriasis from the Latin word for rain. This is more common in children and young adults. Guttate psoriasis is short-lived and can disappear without treatment.

The nails may also be affected by psoriasis. It is estimated that 10% of people with psoriasis have visible changes only in the nails. Nail changes include yellow-brown spots under the nail ("oil spots"), pitting (pinpoint depressions on the nail surface), separation of the nail from the base at the furthest edge, and thickening that can mimic fungal infection of the nails.

Review Date: 07/27/2006
Reviewed By: Shlomit Halachmi, MD, PhD, Private Practice Specializing in Dermatology, Somerville, MA. Review provided by VeriMed Healthcare Network.