Psoriatic arthritis develops when the immune system inappropriately attacks the body's own tissues. The tissues in an affected individual that become damaged and destroyed by the immune system are those that line the joints and make up the skin. The autoimmune process that causes symptoms of psoriatic arthritis can be progressive or recurring. When other methods of treatment fail to manage the symptoms, immunosuppressants can be used to calm down the overactive immune system that is attacking the tissues of the skin and joints. The immune system is less likely to attack and cause damage to the healthy tissues in the body when its actions are toned down with medication.