Psoriasis is the most common autoimmune disease in the United States. As many as 7.5 million Americans live with psoriasis and 80% of those have plaque psoriasis.
What is an autoimmune disease? Autoimmune diseases occur when the body's immune system attacks and destroys healthy body tissue by mistake. There are more than 80 types of autoimmune diseases, including plaque psoriasis.
Plaque psoriasis appears on the skin as raised, red patches covered with a silvery buildup of dead skin cells. These patches can be itchy and painful, and most often appear on the knees, elbows, lower back, and scalp but can appear anywhere on the body.
Up to 30% of people with psoriasis also develop psoriatic arthritis, which causes pain, stiffness, and swelling in and around the joints. Psoriatic arthritis can develop at any time, but it most commonly appears between the ages of 30 and 50 years. In people with psoriatic arthritis, the immune system is thought to turn against itself. Inflammation can occur, which may cause the tissue surrounding the joints to thicken. Over time, this may result in a swollen joint.