In psoriasis, however, the rates of cell multiplication and growth is abnormally rapid and disordered, so that skin sheds every three to four days rather than about every month. The overproduction of skin cells lead to thickening of the skin and scaling. Silvery plaques occur most frequently on the scalp, elbows, knees and lower back, but can occur almost anywhere on the skin. The psoriatic process in any given area is reversible. Consequently, the involved skin may return to a normal appearance without scarring whenever this process is reversed, either spontaneously or as a result of treatment.
Psoriasis is neither infectious nor contagious.
Injury to the skin commonly precipitates the appearance of psoriatic lesions. If the skin is cut, scratched, rubbed or severely sunburned, a flare-up often will occur 10 to 14 days after the skin is irritated. General health factors may influence psoriasis. Many patients note flare-ups of the disease during physical and emotional stress. Infections can aggravate psoriasis.