Acropustulosis is a rare form of pustular psoriasis that causes pus-filled blisters to form on the tips of your fingers and toes, often beneath the nails. It's more likely to affect your fingers than toes, and it often happens after you get injured. The blisters can make your nails become deformed or fall off. In severe cases, the bones on your fingers and toes may change shape or become deformed.