The exact cause of psoriatic arthritis is not known. Genetic factors, environmental factors and immunological factors do play an important role in the manifestation of this condition.

People with a family history of this condition are more likely to develop it at some point in their lives. The common age for the onset of this disease is between 30 and 50 years. Psoriatic arthritis is more frequently seen in men rather than in women. These facts indicate that there could be a genetic cause for this condition. A gene marker called HLS-B27 is also frequently, though not always seen in people with psoriatic arthritis. Scientists believe that certain gene mutations are associated with this disease.

Changes in the immune system are also thought to be linked to psoriatic arthritis. People with this disease show increased levels of B cells, T-cells, chemokines and cytokines. These are cells and chemical mediators of the immune system, which are responsible for the inflammation and tissue damage associated with this condition.

Sometimes, infections like streptococcal infections render a person more susceptible to psoriatic arthritis. It is also frequently seen in HIV positive people. This indicates that there may be a link between bacterial or viral infections and psoriatic arthritis.