"Erythema" means red-colored. "Nodosum" means nodules (lumps or bumps).
Erythema nodosum is an inflammatory reaction in the layer of fat under your skin. It causes red or purplish bumps under your skin, often on your shins.
Common causes include:
Less common causes:
Doctors can usually tell you have erythema nodosum by looking at the bumps on your skin. Sometimes to know for sure they'll do a biopsy (take out a small piece of tissue to look at under a microscope).
To find out what's causing your erythema nodosum, they may do other tests, such as:
Skin test for tuberculosis
Erythema nodosum gets better on its own after 3 to 6 weeks. If your erythema nodosum is caused by an infection, doctors will treat the infection. The following may help you lessen pain: