What causes psoriasis?

While most skin issues might make you think that there’s something environmental (like fabrics or chemical irritants) causing that flare-up, that’s not usually the case with psoriasis. Psoriasis is an autoimmune disease, which means it’s caused by an overactive immune system. In psoriasis, the overactive immune system attacks your body’s normal tissues and causes skin cells to grow faster. Those cells don’t shed normally, so they pile up on the surface of the skin, which is what causes those red, rough, or raised patches (called “plaques”) and other skin problems.