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What is erythema nodosum?
Erythema nodosum is a skin condition that causes a lumpy red rash, usually on your lower legs. It is sometimes caused by an illness, but more than half the time there is no reason found for it.
Anyone can get erythema nodosum, but it is most common in females aged 20 to 40 years.
What are the symptoms of erythema nodosum?
Painful red lumps, or nodules, gradually appear on your skin over a week or longer. They usually appear on both legs, from the knees down. Occasionally, they can also appear on your thighs, arms or face.
The lumps can be as small as a grape or bigger than an orange. They start off bright red and gradually become flatter and turn purple or dark red, similar to a bruise. They fade away without leaving a scar.
Other symptoms can include:
- swollen ankles
- fever
- feeling unwell
- aching joints
- diarrhoea
- abdominal pain
What causes erythema nodosum?
Erythema nodosum develops when the layer of fat under your skin becomes inflamed or irritated.
It can be triggered by:
- a reaction to medicines, such as the contraceptive pill
- a streptococcal (‘strep’) throat infection
- pregnancy
It can also occur in people who have:
- inflammatory bowel disease, such as Crohn’s disease or ulcerative colitis
- cancer
- tuberculosis
- sarcoidosis
In about half of all people who get erythema nodosum, doctors can’t identify the cause.
How is erythema nodosum diagnosed?
The rash can be diagnosed by a doctor based on your symptoms and how the lumps look and feel. Sometimes your doctor will take a biopsy of your skin to check that the diagnosis is right.
Your doctor might also refer you for some tests to check if another illness is causing your erythema nodosum.
These tests may include:
- blood tests
- a throat swab to check for streptococcal infection
- a chest x-ray
- a skin test (a Mantoux skin test, which checks for tuberculosis)
- a urine test
- a stool test
How is erythema nodosum treated?
Your doctor will treat any illness that is causing erythema nodosum. This usually makes your symptoms go away.
Treatment to relieve your symptoms may include:
- anti-inflammatory medicine — check with your pharmacist or doctor if you can take these
- wearing support stockings
- resting with your legs elevated
- cold packs
For most people, erythema nodosum clears up by itself within 2 to 6 weeks. Pain and swelling can take a few weeks longer to go away. Talk to your doctor if you’re not getting better — there are other medicines that can help.
