The Arthritis Association estimates that about 30 percent of people with psoriasis have psoriatic arthritis. It's an autoimmune condition, in which your immune system attacks healthy tissue in your joints and skin. This results in inflammation, causing joint swelling, pain, and stiffness.
Causes of inflammation include: Chronic low-grade food allergies or food sensitivities that may cause few symptoms. An imbalance of bacteria and fungi in your gastrointestinal tract, also known as dysbiosis. This causes your immune system to overreact to bacteria in your gut and can be without notable symptoms.