Plaque psoriasis is the most common type of psoriasis. Approximately 80% of people who develop psoriases are diagnosed with this form of psoriasis, which appears as patches of raised, reddish skin covered by silvery-white scale. Although the plaques can occur anywhere on the body, scalp, knees, elbows, and lower back are the parts of the body which are frequently affected by these plaques or patches.

This form of psoriasis is most typically differentiated by circular-to-oval red plaques that are distributed over extensor body surfaces and the scalp. Dermal Inflammation and epidermal hyperproliferation are the factors that the plaques usually exhibit scaling.

The duration and extent of plaque psoriasis is highly variable from patient to patient, and psoriatic arthritis, a related form of arthritis known as psoriatic arthritis, which causes inflammation of the joints is suffered by between 10% and 30% of the people who get psoriasis, is also experienced by up to 10-20% of plaque psoriasis patients. Relapses or acute flares of this type of psoriasis may also evolve into more severe disease, erythrodermic or pustular psoriasis for example.

Plaque psoriasis is suffered by 1 to 2% of the American population. Family history has been shown to foretell disease occurrence. The rate in siblings of probands is as high as 50% when both parents have psoriasis, and the rate is 16.4 when one parent is affected. Only 7.8% of siblings of probands are observed as affected when neither parent is affected by psoriasis. 36-71% of psoriasis patients have been shown in other studies to have one relative who is also a psoriasis patient.