It is not uncommon for those suffering from Crohn’s Disease, like yourself, to have dermatological manifestations of the disease. The skin lesions you are describing could be directly related to the Crohn’s Disease but it can also be secondary to a vitamin deficiency secondary to malabsorption. One of the more commonly described vitamin deficiencies due to Crohn’s disease is Vitamin B deficiency.
Pellagra is a disease associated with Vitamin B3 (niacin) deficiency and results in rashes, skin lesions, dementia, diarrhea. The symptoms and severity of the disease vary with the extent of vitamin deficiency.
You should be evaluated by your primary care physician for a physical exam and lab tests to determine if your dermatitis is secondary to a vitamin deficiency or a systemic process.