Psoriasis is a skin disease that causes scaling and swelling. Most cases of psoriasis cause patches of thick, red skin with silvery scales and it may be itchy or sore. Factors that can cause the psoriasis to worsen include infections, stress, changes in the weather, and certain medication. It occurs mainly on the elbows, knees, legs, lower back, and scalp. It is not contagious. Psoriasis develops when the rate of skin cell turnover is abnormally fast – the process taking days instead of weeks as it should. Treatments include topical medications, light therapy, oral medication, nutritional therapy, herbal therapy, and Ayurveda.