Both rheumatoid arthritis (RA) and psoriatic arthritis (PsA) are conditions that damage your joints, causing swelling, stiffness, and pain. Both are autoimmune diseases. When you have RA, your immune system attacks the lining of the tissues around your joints. They swell up and become painful. Over time, they can become damaged and deformed.
With PsA, your immune system attacks and damages not just your joints, but your skin as well. It causes your body to make too many skin cells, which leads to psoriasis, a skin condition that often affects people with PsA.