Besides psoriatic arthritis, there appears to be an association between psoriasis and several other skin and medical conditions. Reiter's syndrome, sacroileitis, and ankylosing spondylitis all seem to share common causes. Inflammatory bowel diseases, such as ulcerative colitis and Crohn's disease, may increase the risk of psoriasis by 5 to 10 times.
Although not as strongly associated as the above, certain blistering diseases like bullous pemphigoid or pemphigus may be associated with psoriasis.
HIV seems to increase the risk of psoriasis as well as its "lesser cousin," seborrheic dermatitis. Autoimmune disorders such as thyroiditis and lupus are less strongly associated with psoriasis.
