Psoriasis is a common skin condition that causes skin redness and irritation. Most people with psoriasis have thick, red skin with flaky, silver-white patches called scales.
Causes, incidence, and risk factors
Psoriasis is a very common condition. The disorder may affect people of any age, but it most commonly begins between ages 15 and 35.
The condition cannot be spread to others.
Psoriasis seems to be passed down through families. Doctors think it probably occurs when the body’s immune system mistakes healthy cells for dangerous substances and starts an inflammatory cycle.
Skin cells start at the lower level of the epidermis (the outer layer of the skin) and normally rise to the surface about once a month. In persons with psoriasis, this process is too fast (about 2 weeks instead of 4 weeks) and dead skin cells build up on the skin’s surface.
The following may trigger an attack of psoriasis or make the condition more difficult to treat:
- Bacteria or viral infections, including strep throat and upper respiratory infections
- Dry air or dry skin
- Injury to the skin, including cuts, burns, and insect bites
- Some medicines, including antimalaria drugs, beta-blockers, and lithium
- Too little sunlight
- Too much sunlight (sunburn)
- Too much alcohol
Up to one-third of people with psoriasis may also have arthritis, a condition known as psoriatic arthritis.