What causes psoriatic arthritis?
The arthritis and the skin condition are both caused by inflammation. The processes of inflammation are very similar in the skin and the joints.
We don't yet know exactly what triggers the inflammation in psoriatic arthritis, although a particular combination of genes makes some people more likely than others to develop psoriasis and psoriatic arthritis.
Research suggests that something – perhaps an infection – acts as a trigger in people who are already at risk of this type of arthritis because of the genes they've inherited from their parents. No specific infection has yet been found, and it may be that a variety of infections can trigger the disease, for example bacteria that live in patches of psoriasis.
Sometimes the arthritis can follow an accident or injury, particularly if it affects a single joint. People who are overweight are more at risk of developing both psoriasis and the arthritis linked with this.