Pustular psoriasis is a skin disease. You'll see white bumps filled with pus near or inside red skin blotches. These are called pustules. They can hurt and be scaly, flaky, or itchy. It occurs due to a problem with the immune system that results in an overgrowth of skin cells, leading to skin changes. Pustular psoriasis is a rare and severe form of psoriasis that involves widespread inflammation of the skin and small white or yellow pus-filled blisters or pustules.