Picture of Erythema Nodosum
Erythema nodosum is a reaction pattern in the skin due to a bacterial strep throat infection or psittacosis, tuberculosis, sarcoidosis (inflammation of the lymph nodes or other organs), fungal infections such as coccidioidomycosis or histoplasmosis, inflammatory bowel disease (Crohn's disease or ulcerative colitis), cancer, pregnancy, or a hypersensitivity reaction to drugs such antibiotics containing penicillins or sulfa, oral contraceptives, bromides or iodides. They eventually fade on their own without treatment and leaving behind a flat bruise.
Text Source: Johns Hopkins Medicine
National Library of Medicine