Psoriasis is a chronic inflammatory skin disease that causes skin cells to multiply up to 10 times faster than normal. The main symptoms are white scaly patches of skin that may itch.  They can grow anywhere, but most appear on the scalp, elbows, knees, and lower back. Psoriasis can’t be passed from person to person. It does sometimes happen in members of the same family. Psoriasis is an autoimmune disease. Certain triggers may make your symptoms worse, including: Cold, dry weather, Stress, Some medicines, Infections, Skin Injury, Alcohol and Smoking.