What is psoriasis?

Psoriasis is a chronic (long-lasting) skin disease that causes raised, red patches on your skin. The patches can be large or small, and they can appear anywhere on your body, especially your elbows, knees, and scalp.

Doctors aren't sure exactly what causes psoriasis. It may involve a problem with your immune system.

Psoriasis tends to run in families.

Psoriasis tends to come and go, although some patches may never go.

Flare-ups can be triggered by skin injuries, sunburn, infections (such as colds and strep throat), winter weather, drinking alcohol, high stress levels, and certain medicines. Flare-ups are more common for people who are overweight, smoke tobacco, or have HIV infection.

Symptoms of psoriasis include one or more raised, red skin patches with silver scales on your scalp, elbows, knees, low back, or buttocks. Skin patches may also show up on your eyebrows, armpits, belly, around the anus, or between your buttocks. The patches may itch or hurt.

Some people with psoriasis have other symptoms such as swollen painful joints or pus-filled blisters.

Sometimes, your fingernails are misshapen, thick, and pitted.

Doctors usually can tell you have psoriasis by the way your skin patches look. If doctors aren't sure, they'll take a sample of your skin to look at under a microscope (biopsy).

Doctors will give you one or more treatments such as medicines to put on your skin and phototherapy, which is when UV light is shined on your skin to heal it.

Medicine given as pills or a shot are also used to treat psoriasis, but some of these medicines have side effects, so they're only used to treat severe cases.