The most common accompanying disorders are Streptococcal infection (especially in children) Sarcoidosis Inflammatory bowel disease Other possible triggers include Other bacterial infections (eg, Yersinia, Salmonella, mycoplasma, chlamydia, leprosy, lymphogranuloma venereum, tuberculosis) Fungal infections (eg, kerion, coccidioidomycosis, blastomycosis, histoplasmosis) Rickettsial infections Viral infections (eg, Epstein-Barr, hepatitis B) Use of drugs (eg, sulfonamides, iodides, bromides, oral contraceptives) Hematologic and solid cancers Pregnancy Behçet disease Up to one third of cases of erythema nodosum are idiopathic.