Psoriatic arthritis, or PsA, is a particular type of arthritis (joint inflammation) that develops in individuals with psoriasis, a skin condition that causes painful, itchy, and flaky skin rashes. Psoriatic arthritis can occur in any joint in the body. 30-50% of the 7.5 million Americans with psoriasis will develop psoriatic arthritis, and even fewer will develop severe forms of the condition.