The causes of erythema nodosum are mostly thought to be related to infections, including streptococcal infections, tuberculosis, intestinal infections and systemic fungal infections (Dentamoeba, Coccidioides and Sporotrichum), which can cause the disease. Some drugs such as sulfonamides, bromides, iodides, and contraceptives can also cause erythema nodosum. The pathogenic mechanism of the above factors is not known, but may be due to a delayed metamorphic reaction of the organism to the pathogen. Behçet’s disease, Sweet’s syndrome, lupus erythematosus, and ulcerative colitis often present with erythema nodosum-like damage, which may be due to the involvement of the subcutaneous fat by the corresponding disease, rather than the coexistence of the two diseases.