Erythema Nodosum: Symptoms, Causes, Diagnosis, and Care

Erythema nodosum (EN) is an inflammatory reaction in the fat layer beneath the skin. It often causes painful, warm nodules on the fronts of the lower legs. The nodules can change color as they fade, sometimes looking like bruises. EN may follow an infection, occur with a medicine or another health condition, or develop without a clear cause.

Medical information: New tender nodules should be assessed by a healthcare professional, particularly when there is fever, joint swelling, breathing or chest symptoms, pregnancy, or a possible medicine reaction. This article cannot identify the cause or replace individual care.

What erythema nodosum is

Erythema nodosum is a type of panniculitis, meaning inflammation in the layer of fat beneath the skin. In EN, inflammation is usually concentrated in the connective tissue partitions around fat cells. This is deeper than the surface redness seen in many ordinary rashes, which helps explain why EN nodules feel tender and firm beneath the skin rather than like a small surface pimple.

EN is often a reaction to another event rather than a skin infection on its own. The immune system responds to an infection, medicine, inflammatory disease, pregnancy-related change, or another trigger, and tender nodules appear. Sometimes an evaluation does not identify a trigger. The British Association of Dermatologists and NHS both note that many episodes improve on their own over several weeks, while clinicians still look for an underlying cause when the history suggests one.

Because the nodules sit in deeper tissue, they may not form a head, drain, or ulcer. They can feel like a bruise or a deep bump. The skin above them may be red, dusky, or darker than the surrounding skin. As inflammation settles, the color often changes toward purple, brown, or yellow-green, much like a resolving bruise.

EN itself is not contagious and is not usually a permanent skin disease. If an infection triggered the reaction, that infection may have its own contagiousness and may need treatment. The nodule is the body's inflammatory response; it does not mean bacteria are spreading through the skin.

Common signs and symptoms

The most typical sign is a group of tender nodules on the front of the lower legs, often on both sides. They may also appear near the knees or ankles, and less often on the thighs, arms, or other areas. Nodules vary in size and number. The area may feel warm and sore when touched, when clothing rubs, or when walking puts pressure on the legs.

At first, the overlying skin may appear bright red, pink, or a deeper shade that contrasts with a person's usual skin tone. In brown or Black skin, redness may be less obvious, and the nodules can appear darker than nearby skin. Color alone is not enough to distinguish EN from other conditions. The location, depth, tenderness, timing, and progression are all considered.

Over days to weeks, nodules often become flatter and bruise-like. They generally do not open or leave a permanent scar. Pain and swelling can interfere with standing, walking, work, caregiving, or exercise. The course may be one episode, a recurrence, or a longer period with new nodules appearing while older ones fade.

Some people also feel generally unwell. Symptoms can include fever, fatigue, aches, ankle swelling, or joint pain, especially around the ankles and knees. A sore throat or respiratory illness may have occurred before the nodules. Digestive symptoms can be relevant if inflammatory bowel disease or an intestinal infection is being considered.

EN is not the same as erythema multiforme, which usually forms target-like spots on the skin, or erythema migrans, the expanding rash associated with Lyme disease. The word “erythema” simply refers to redness and appears in the names of several unrelated conditions. If the diagnosis is uncertain, a clinician can distinguish among them and other types of panniculitis.

What can trigger erythema nodosum?

EN can follow a wide range of events. A common trigger is a recent infection, particularly a sore throat caused by streptococcal bacteria. Other respiratory or gastrointestinal infections can also be considered, depending on the person's symptoms, location, and exposures. Some infections are more relevant in certain regions or after travel, so clinicians ask about timing and exposures rather than ordering every test for every person.

Medicines are another possible trigger. Certain antibiotics, sulfonamide medicines, and hormonal medicines have been associated with EN. The timing between starting a medicine and developing nodules matters, but timing alone does not prove the medicine caused the reaction. Never stop a prescription, contraceptive, or long-term medicine on your own. Ask the prescriber to review whether the medicine could be related and what safer alternatives exist.

Inflammatory conditions can be associated with EN. Examples include sarcoidosis and inflammatory bowel disease such as Crohn's disease or ulcerative colitis. Less commonly, other inflammatory or blood conditions may be involved. A clinician may ask about persistent cough, shortness of breath, diarrhea, abdominal pain, blood in the stool, joint swelling, or unexplained weight changes to decide whether additional assessment is needed.

Pregnancy can be associated with EN. If nodules develop during pregnancy or soon after delivery, the person should contact their obstetric clinician or primary care clinician. Some possible treatments for pain may not be safe in pregnancy, and the medical team can choose an appropriate evaluation and symptom plan.

Sometimes no cause is identified even after an appropriate evaluation. That does not mean the symptoms are imagined or that the evaluation failed. A self-limited inflammatory reaction can occur without a clear trigger. Reassessing is reasonable if nodules persist, return, or new symptoms emerge.

How clinicians evaluate the nodules

The first step is a medical history and examination. A clinician may ask when the nodules appeared, whether they are on one or both legs, how painful they are, whether they change like bruises, and whether there has been a recent sore throat, cough, digestive illness, travel, new medicine, pregnancy, or joint symptoms. The clinician may also ask about known inflammatory disease and previous episodes.

Typical EN can often be recognized from the location and appearance of the nodules. Not everyone needs a skin biopsy. If the pattern is unusual, the nodules are not on the usual areas, the skin is ulcerating, or the diagnosis remains uncertain, a biopsy may help distinguish EN from another form of panniculitis. Because the affected tissue is deep, the clinician chooses a sample that reaches the relevant layer.

Tests are used to look for a likely trigger when it would affect care. Depending on the history, the clinician may request blood tests, a throat swab or other strep testing, a chest X-ray, or evaluation of digestive symptoms. Chest imaging may be considered when sarcoidosis or certain infections are plausible. Testing for tuberculosis or fungal infection depends on individual risk and symptoms. A normal result does not always identify why EN occurred.

The aim is not to search for every rare disease. Instead, the clinician prioritizes possibilities that fit the person's symptoms, age, location, exposures, and examination. The published practical diagnostic review outlines this targeted approach, and Healthdirect Australia describes common tests such as blood work, a throat swab, chest imaging, and occasional biopsy.

Other nodular skin problems can require different treatment. These include venous inflammation, vasculitis, infection in the fat layer, traumatic panniculitis, and other inflammatory disorders. Ulceration, drainage, a single rapidly enlarging lump, an unusual location, or a course lasting longer than expected may prompt a closer evaluation. The physician may refer to dermatology, rheumatology, infectious disease, or another specialist according to the findings.

Treatment and symptom relief

Treatment has two goals: relieve discomfort and address an underlying trigger when one is found. Many episodes gradually settle over several weeks. If a bacterial infection is identified, a clinician may prescribe an antibiotic for that infection. Antibiotics do not treat EN itself when no bacterial cause is present. If a medicine may have caused the reaction, the prescriber decides whether to change it.

During a painful flare, resting with the legs raised may ease throbbing or swelling. A cool, damp cloth can soothe tender areas. Some people need to limit long periods of standing, running, or walking until pain improves. A clinician or pharmacist may discuss supportive garments or compression if they are appropriate for the person's circulation and diagnosis.

Anti-inflammatory pain medicines such as NSAIDs may help some people, but they are not suitable for everyone. Kidney disease, stomach ulcers, blood-thinning medicines, pregnancy, some allergies, and inflammatory bowel disease can change the risk. Ask a clinician or pharmacist before starting an over-the-counter medicine, especially if there are other health conditions or regular prescriptions.

For persistent or recurrent EN, treatment may involve a specialist and depends on the diagnosis and the cause. Prescription anti-inflammatory medicines are not a routine do-it-yourself option. For example, systemic corticosteroids can be unsafe in some situations if an infection has not been recognized, so clinicians first consider whether infection or another cause needs treatment.

Recovery can take longer than the skin color suggests. Nodules may be less painful while bruise-like marks remain, and ankle swelling or joint discomfort can continue after the skin begins to fade. Follow the care plan and arrange a review if symptoms worsen, new areas appear, or the course does not match what the clinician expected.

EN may recur in some people. A recurrence does not automatically mean that a serious disease is present, but a new episode may warrant another look at recent infections, medicines, and associated symptoms. Keep a list of dates and medication changes if this helps the clinician assess patterns.

Special considerations

Pregnancy

Because EN can occur during pregnancy and medication choices may need to change, report new painful nodules to an obstetric or primary care clinician. The clinician can decide whether tests are needed and which pain-relief options fit the pregnancy. Do not assume a medicine is safe because it is available without a prescription.

Children and teenagers

EN can occur at any age, including childhood. A child with tender nodules may also have fever or joint pain. A clinician can check for a recent infection and decide if additional testing is appropriate. Caregivers should not give adult medicines or leftover antibiotics without professional advice.

Inflammatory bowel disease

EN may appear alongside Crohn's disease or ulcerative colitis. People with bowel disease should tell the clinician whether diarrhea, abdominal pain, blood in the stool, or other symptoms are changing. Some anti-inflammatory pain relievers may be unsuitable for certain people with bowel inflammation, so ask the treating clinician before using them.

Medication changes

If a new medicine is suspected, bring the package or a current medication list to the appointment. Do not discontinue contraception, antibiotics, blood pressure medicine, or any other prescribed treatment without advice. A clinician can weigh the possibility of a drug reaction against the reason the medicine was prescribed.

When to seek medical care

Arrange a clinical assessment for new tender nodules, especially if they are numerous, interfere with normal walking, recur, or come with fever or joint swelling. Also book an appointment if nodules do not improve over several weeks or remain after about eight weeks. A clinician can confirm whether the pattern fits EN and decide whether an underlying cause needs investigation.

Seek urgent care for severe illness, difficulty breathing, chest pain, fainting, confusion, a high or persistent fever, rapidly worsening swelling, or severe joint pain. These symptoms may have a cause beyond EN and should not be managed solely with rest at home. If the nodules develop an open sore, drain, or look very different from a typical pattern, seek medical review promptly.

When EN is diagnosed, ask what symptoms should prompt an earlier return and how long recovery is expected to take. If a likely cause is identified, ask whether it needs treatment or follow-up. When no cause is found, confirm whether the clinician recommends monitoring only or a planned reassessment.

Preparing for an appointment

A few details can help make the visit more productive. Write down when the nodules began, how they changed, whether they appeared on both legs, and what makes the pain better or worse. Note recent throat or respiratory symptoms, stomach or bowel symptoms, travel, new medicines, and pregnancy status when relevant.

Bring a current medication list with start dates if possible. If the skin changes over time, a clinician may find dated photographs useful; take them in consistent light and avoid pressing on the nodules. A photo can document changes but cannot replace a physical examination or establish the diagnosis.

Useful questions include: Does the pattern look typical for EN? What causes are most relevant in my case? Which tests are useful, and why? Do I need a biopsy? Which pain medicines are safe with my other conditions? How should I manage standing or walking while it heals? When should I return if it does not improve?

Ask the clinician what to do if another episode occurs. If a recent infection, inflammatory disease, pregnancy, or medicine is relevant, ask whether follow-up with another specialist is needed. Keeping one coordinated plan can reduce repeated testing and avoid changing medicines without clear guidance.

Common misconceptions

“The nodules are a skin infection.” EN is inflammation in the tissue beneath the skin. An infection can trigger the reaction, but the nodules themselves are not contagious or usually caused by germs multiplying in the skin.

“Every case has the same trigger.” Triggers vary, and sometimes no cause is found. A clinician focuses on the person's history and symptoms rather than assuming that one infection or medicine explains every case.

“Bruise-like color means the condition is getting worse.” Nodules often change color while settling. However, worsening pain, new nodules, fever, or persistent swelling should be reviewed rather than judged by color alone.

“A biopsy is required for everyone.” Many typical cases are diagnosed from examination. A biopsy may be useful when the presentation is atypical or another panniculitis must be ruled out.

“Pain medicine is safe for everyone.” Over-the-counter anti-inflammatory drugs can have risks with pregnancy, kidney or stomach conditions, some medicines, and inflammatory bowel disease. Ask a professional what fits your situation.

Frequently asked questions

Sources and further reading

• British Association of Dermatologists. Erythema nodosum patient information.
• National Health Service. Erythema nodosum.
• Healthdirect Australia. Erythema nodosum: symptoms, causes, diagnosis, and treatment.
• DermNet. Erythema nodosum.
• Pérez-Garza DM et al. Erythema Nodosum: A Practical Approach and Diagnostic Algorithm. 2021.

Editorial note: This article is general educational content and cannot diagnose skin nodules or replace individualized medical care.