I found this online, hope this helps:
Several types of skin rash can accompany Crohn's disease. None of these rashes are unique to Crohn's, however. They can occur on their own or can accompany other diseases.
- Pyoderma gangrenosum. This is a type of skin ulcer. It tends to appear on the lower legs but can occur anywhere. It starts with a small bump or blister, then expands to a deep, painful ulcer. Multiple ulcers can appear at once. Pyoderma gangrenosum can appear even if intestinal disease is under control.
- Erythema nodosum. This is an inflammation of fat underneath the skin's surface. It appears as red, painful lumps on the lower legs and sometimes on the thighs or arms. It tends to appear when intestinal disease is more active.
- Necrotizing small vessel vasculitis. Vasculitis is an inflammation of blood vessels which leads to bleeding underneath the skin. It can appear as small red spots or larger bruises, usually on the legs or arms.