Some doctors recommend salicylic acid ointment, which smoothes the skin by promoting the shedding of psoriatic scales. Using salicylic acid over large areas of skin, however, may cause the body to absorb too much of the medication, leading to side effects. Salicylic acid may also cause skin irritation and weaken hair shafts, which can cause breakage and temporary hair loss. The effectiveness of these treatments are modest at best.