Psoriasis is an autoimmune disease and is characterized by raised areas of skin.
These areas are typically red, or purple on some people with darker skin, and may be dry, itchy or scaly. Psoriasis may present itself in small, localised patches to complete body coverage.
There are five main types of psoriasis: plaque, guttate, inverse, pustular and erythodermic.
Plaque (or vulgaris) is the most common form of psoriasis and makes up about 90% of cases. It typically presents as red patches with white scales on top. Areas most commonly affected are the back of the forearms, shins, navel area, and scalp.
Guttate psoriasis has drop-shaped lesions.
Pustular psoriasis presents as small pus-filled blisters that are noninfectious.
Inverse psoriasis forms red patches in skin folds.
Erythrodermic psoriasis occurs when the rash becomes very widespread, and can develop from any of the other types.
Fingernails and toenails are affected in most people with psoriasis at some point in time and this may include pits in the nails or changes in nail colour.
Psoriasis is generally thought to be a genetic disorder that may be triggered by environmental factors or stress and involves the immune system reacting to skin cells.