You have psoriasis

Having the skin condition psoriasis is the biggest risk factor for developing psoriatic arthritis. Both are autoimmune disorders caused by an immune attack on the body. 

Between 5% and 10% of people with psoriasis develop psoriatic arthritis, so watch for joint trouble if you have the skin condition. In rare cases, some people develop psoriatic arthritis before psoriasis (or before it's obvious), says Guy Fiocco, MD, an assistant professor of medicine at the Texas A&M Health Science Center College of Medicine, in Bryan.