Psoriasis is an immune-mediated disease which affects the skin and joints.
It commonly causes red scaly patches to appear on the skin.
The scaly patches caused by psoriasis are often called psoriasis plaques or lesions.
Psoriasis plaques are areas of excessive skin cell production and inflammation.
Skin rapidly accumulates at these sites and sometimes takes a silvery-white appearance.
Plaques frequently occur on the skin of the elbows and knees, but can affect any area including the scalp and genitals.
Psoriasis is not contagious; it cannot be passed from person to person.