Psoriasis is a common, chronic, relapsing/remitting, immune-mediated systemic disease characterized by skin lesions including red, scaly patches, papules, and plaques, which usually itch. The skin lesions seen in psoriasis may vary in severity from minor localized patches to complete body coverage.

The five main types of psoriasis are plaque, guttate, inverse, pustular, and erythrodermic. Plaque psoriasis is considered the most common form.