Psoriasis is a chronic inflammatory disease of the skin with a likely immunologic basis. Hyperproliferation of epidermal cells results in thickened, scaly skin. Psoriasis is commonly categorized as mild (covers less than 3% of the body), moderate (3%-10%), or severe (over 10%). Psoriasis is fairly common in childhood but rare in infancy (infantile psoriasis).

There are many differing clinical patterns of psoriasis, including plaque type, guttate psoriasis (which often follows strep throat), palmar-plantar psoriasis, erythrodermic psoriasis, and pustular psoriasis. Involvement of the inguinal areas and axillae is termed inverse psoriasis.

Psoriasis can involve the nails (up to one-third of 313 children in one study) and may also be limited to the fingernails or to body areas such as the genitals, scalp, feet, or even a solitary fingertip. Psoriasis can often be seen in the diaper area and in the skin folds of very young children.

Anogenital psoriasis is rather common and usually is comparable to psoriasis found elsewhere on the body. It can be isolated to the genitalia but often is part of a more generalized affliction. In males, inverse psoriasis is found on the scrotum, perirectal skin, and inguinal folds. Penile psoriasis is found on the glans and under the foreskin.