TNF and inflammatory bowel disease: The link of psoriasis and IBD relies on three main epidemiologic links: (1) higher incidence of psoriasis in patients with Crohn’s disease (CD) and ulcerative colitis (UC), (2) predisposition to CD and UC in patients with psoriasis, and (3) high risk of iatrogenic psoriatic lesions in patients with IBD treated with anti-TNF agents.