Arm of a patient with mild psoriasis. Psoriasis is a common, chronic relapsing/remitting immune-mediated skin disease characterized by 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 disease affects 2??% of the general population. There are five main types of psoriasis: plaque, guttate, inverse, pustular, and erythrodermic. Plaque psoriasis is the most common form and typically manifests as red and white scaly patches on the top layer of the skin. Skin cells rapidly accumulate at these plaque sites and create a silvery-white appearance.