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.

Psoriasis is very common. Anyone can get it,  but it most commonly begins between ages 15 and 35.

It is not contagious. You cannot spread it 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.

Usually, skin cells grow deep in the skin and rise to the surface about once a month. In persons with psoriasis, this process is too fast. 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
• Stress
• Too little sunlight
• Too much sunlight (sunburn)
• Too much alcohol

In general, psoriasis may be severe in people who have a weakened immune system. This may include persons who have:

• AIDS
• Cancer chemotherapy