What is erythema nodosum?

Erythema nodosum is a skin condition of the fat that lies just below your skin (the subcutaneous layer). It’s often a reaction to an infection or medicine. But it may occur for no known reason. It causes tender, red bumps to form, usually on the shins that may become purplish in color within a few days. The bumps may also appear on other parts of the body, such as the ankles, thighs, arms, or face.

Erythema nodosum is usually not a serious condition. Symptoms often go away within 6 weeks. But they may appear again. As the bumps fade, they may look like bruises.

What causes erythema nodosum?

Erythema nodosum may have no known cause. It can sometimes be linked to pregnancy or it may be a sign of some other infection, disease, or sensitivity to a medicine. Diseases that may cause this skin problem are:

• Streptococcal infections.

• Inflammation of the lymph nodes and other organs, such as sarcoidosis.

• Infections of the upper respiratory tract and lungs, such as coccidioidomycosis, histoplasmosis, psittacosis, or tuberculosis.

• Ulcerative colitis or Crohn’s disease.

• Cancer.

Medicines that may cause erythema nodosum are:

• Antibiotics containing sulfa or penicillin.

• Bromides.

• Iodides.

• Birth control pills.

Who is at risk for erythema nodosum?

Anyone can develop erythema nodosum. But these things may raise your risk: 

• Being female

• Being in your 20s or 30s

• Having a family history of the condition

• Having inflammatory bowel disease

What are the symptoms of erythema nodosum?

These are the most common symptoms of erythema nodosum:

• Red, sore bumps on the shins that may become purplish in color within a few days

• Fever

• Fatigue

• Joint pain or swelling

• Enlarged lymph nodes in the chest

These symptoms may look like other skin conditions. Always talk with your health care provider for a diagnosis.

How is erythema nodosum diagnosed?

Your provider will ask about your health history and do a physical exam. You may also need 1 of these tests:

• Blood test. A blood sample can help identify or rule out possible causes, such as an infection.

• Biopsy. Your provider may remove a small sample of tissue from the bump for a biopsy. The tissue sample will be examined under a microscope at a lab.

• Throat swab. This may be done to check for strep throat, 1 of the most common causes of erythema nodosum.

• Other tests. Your provider may use other tests, such as an X-ray or stool cultures, to find out what may be causing the skin condition.

Sometimes the exact cause of erythema nodosum can’t be found.

How is erythema nodosum treated? 

Treatment will depend on your symptoms, age, and general health. It will also depend on how bad the condition is.

You may not need treatment if you have a mild case of erythema nodosum. It often goes away on its own. If your provider recommends treatment, it may include:

• Antibiotics to treat an underlying bacterial infection.

• Treatment of other underlying cause.

• Stopping a medicine, if it is causing the reaction.

• Bed rest and leg elevation to ease pain.

• Nonsteroidal anti-inflammatory medicines.

• Oral corticosteroids.

• A medicine called potassium iodide.

Key points about erythema nodosum

• Erythema nodosum is a skin condition. It causes tender, red bumps, which may become purplish in color within a few days. They usually develop on the shins.

• Erythema nodosum may occur for no known reason. Or it may be a reaction to an infection or medicine.

• A common cause is strep throat, or a streptococcal infection.

• Along with the bumps, symptoms include fever and joint pain.

• A physical exam can help diagnose this skin problem. Other tests may reveal the underlying cause of it.

• Treatment may include medicines, such as antibiotics and nonsteroidal anti-inflammatories.

Next steps

Tips to help you get the most from a visit to your provider:

• Know the reason for your visit and what you want to happen.

• Before your visit, write down questions you want answered.

• Bring someone with you to help you ask questions and remember what your provider tells you.

• At the visit, write down the name of a new diagnosis and any new medicines, treatments, or tests. Also write down any new instructions your provider gives you.

• Know why a new medicine or treatment is prescribed and how it will help you. Also know what the side effects are and when they should be reported.

• Ask if your condition can be treated in other ways.

• Know why a test or procedure is recommended and what the results could mean.

• Know what to expect if you do not take the medicine or have the test or procedure.

• If you have a follow-up appointment, write down the date, time, and purpose for that visit.

• Know how you can contact your provider if you have questions, especially after office hours or on weekends.