These red scaly patches are usually found on the elbows, knees, lower back and scalp although not infrequently patches appear elsewhere including the nails. When psoriasis involves the groin, armpits, genital area and beneath the breasts it tends to be less scaly and have a glazed appearance. Psoriasis infrequently affects the face. It does not cause scarring and rarely results in hair loss.
Psoriasis is very common.
Its exact cause is unknown but the result is skin which grows about seven times more quickly and thickly than usual. It is thought to be due, at least in part, to an abnormal immune reaction against some component of the skin. The rash often seems to start after some sort of trigger factor. These factors should be avoided whenever possible by people with psoriasis. There are probably others that we haven't discovered yet.