Erythema Nodosum: Painful Red Lumps on the Legs and the Warning Signs Not to Ignore
Erythema Nodosum (EN), or painful red lumps on the legs, is inflammation of the fat layer under the skin (panniculitis) caused by an overreaction of the immune system. It appears as raised, red, tender lumps or patches, usually on both shins. The most important point is that EN is not a standalone disease. It is often a "warning sign" of an underlying cause or condition in the body, such as an infection, a medication, or a systemic disease, so it should not be ignored.
In this article, a dermatologist gives a quick overview of what EN is, what causes it, which tests are needed, how to tell it apart from look-alike conditions, the warning signs, and how it is treated.
Quick Facts: Erythema Nodosum
What it is: inflammation of the fat layer under the skin (septal panniculitis) caused by a hypersensitivity reaction
Typical signs: raised, red, tender lumps or patches 1–5 cm in size, usually on both shins, symmetrically
Most common in: women aged 20–40 (about 3–6 times more common than in men)
Course: the lumps do not break open into ulcers and do not form pus. They gradually shrink within 3–6 weeks, change color like a bruise (blue-green to yellow), and heal without scarring
ICD-10: L52
Key point: the "hidden cause" must be found and treated alongside relieving the symptoms
What Causes Erythema Nodosum?
EN is caused by an overreaction of the immune system to a variety of triggers, not by a direct skin infection. In about half of patients, no clear cause is found (idiopathic). In the rest, it is usually linked to the following:
Infections: the most common is streptococcal infection of the throat (strep throat), followed by tuberculosis, fungal infections, and certain gastrointestinal infections
Sarcoidosis: a common systemic cause, especially when EN occurs together with enlarged lymph nodes around the lungs
Inflammatory bowel disease (IBD): Crohn's disease and ulcerative colitis
Medications: such as sulfonamide antibiotics and combined hormonal contraceptive pills
Pregnancy
Behçet's disease and certain cancers (rare, for example lymphoma)
Because the list of possible causes is so broad, seeing a doctor to "find the root cause" matters more than treating only the lumps on the skin.
What Are the Symptoms of Erythema Nodosum?
Raised, red, tender lumps or patches with smooth skin on top and poorly defined edges, felt as deep lumps under the skin
Location: most often on both shins, and sometimes on the thighs, arms, or ankles
They do not break open or form pus and leave no scars once healed
The lumps change color like a bruise, from red to purple, then green, then yellow, before shrinking
Common general symptoms: a low-grade fever, fatigue, and joint pain (especially in the ankles), which often come before or along with the lumps
How to Tell Erythema Nodosum Apart from Similar Conditions
Red lumps or rashes on the legs have many causes. Telling them apart helps ensure correct treatment and avoids missing a more serious condition:
Cellulitis: a bacterial skin infection, usually on one side only, with redness, warmth, swelling, rapid spread, and fever. It needs antibiotics (EN is usually on both sides and does not spread as a single patch)
Thrombophlebitis: painful red lumps in a line along a vein, usually on one side
Erythema induratum / nodular vasculitis: the lumps usually appear on the back of the calf and may break open into ulcers, unlike EN, which appears on the shins and does not ulcerate
Bruises from an injury: there is a history of a knock, and no hard raised lump under the skin
Insect bite or abscess: usually a single spot with a pus head or a puncture mark
Rule of thumb: painful, raised red lumps on both shins that do not ulcerate and heal like a bruise fit EN. But if it is on one side only, spreads quickly, or has ulcers or pus, see a doctor to rule out other conditions
What Tests Are Needed When Erythema Nodosum Is Suspected?
Because EN is a sign of a hidden disease, doctors usually run tests to look for the cause, including:
History and physical examination, for example a sore throat beforehand, digestive symptoms, medications used, and pregnancy
Streptococcal infection tests, such as ASO titer and a throat swab
Chest X-ray to assess for sarcoidosis and tuberculosis
Basic blood tests, such as CBC and ESR/CRP
Skin biopsy is done only in unusual cases or when the diagnosis is unclear, taking a sample deep enough to reach the fat layer
Treatment of Erythema Nodosum
The goal is to treat the underlying cause while relieving symptoms. The approach, in order:
Find and treat the hidden cause, for example giving antibiotics for a strep infection, stopping a triggering medication, or treating a systemic disease that is found
Rest the legs and keep them elevated, and avoid long periods of standing or walking, which helps reduce swelling and pain
Nonsteroidal anti-inflammatory drugs (NSAIDs) to reduce pain and inflammation (avoid in people with contraindications, for example if IBD is suspected, consult a doctor first)
Potassium iodide is an option in some cases under a doctor's supervision
Oral steroids are considered in severe cases that do not respond to treatment, and only after making sure there is no hidden infection
Most cases of EN clear on their own within 3–6 weeks, but looking for the cause is always necessary.
Warning Signs: When to See a Doctor
You should see a doctor to look for the cause whenever EN is suspected, especially if you have:
High fever, severe fatigue, weight loss, or a chronic cough (which may be related to tuberculosis, sarcoidosis, or cancer)
Lumps on one side only, spreading quickly, or with ulcers, pus, or broken skin (this may not be EN but an infection or vasculitis)
Severe joint pain, joint swelling, or chronic digestive symptoms (chronic diarrhea, bloody stools)
Lumps that recur often, or that last longer than 6–8 weeks without shrinking
Pregnant women or people with underlying conditions who have painful red lumps on the legs
Common Misconceptions About Painful Red Lumps on the Legs
"It's just a bruise or a knock, it will go away" — EN usually has no history of injury and is a sign of a hidden disease, so the cause should be investigated
"Painful red lumps on the legs are varicose veins" — these are different conditions. EN is inflammation of the fat layer, not dilated blood vessels
"The lump has to be cut open or drained" — this is unnecessary and should not be done, because EN does not form pus and is not an abscess
"Applying a cream will fix it, no need to find the cause" — topical creams help very little. The key is to find and treat the root cause
Frequently Asked Questions About Erythema Nodosum
What is Erythema Nodosum?
It is inflammation of the fat layer under the skin caused by an immune overreaction, appearing as painful raised red lumps on both shins. It is often a sign that there is an underlying cause or disease in the body.
Are painful red lumps on the legs (Erythema Nodosum) dangerous?
The skin lumps themselves are not dangerous and usually clear on their own within 3–6 weeks. What needs attention is the underlying cause, such as strep infection, tuberculosis, sarcoidosis, or inflammatory bowel disease, so you should see a doctor to look for the cause.
What can cause Erythema Nodosum?
About half of cases have no identifiable cause. The rest are usually due to strep infection, tuberculosis, sarcoidosis, inflammatory bowel disease, certain medications (sulfonamides, contraceptive pills), and pregnancy.
Does Erythema Nodosum go away on its own, and how long does it take?
In most cases the lumps shrink on their own within 3–6 weeks, changing color like a bruise and leaving no scars. The cause still always needs to be investigated, and some people may have recurrences.
What is the difference between Erythema Nodosum and cellulitis?
EN is usually painful red lumps on both shins, symmetrically, which do not spread as a single patch and do not form pus. Cellulitis is a bacterial infection, usually on one side, with redness and warmth that spreads quickly, and it needs antibiotics.
How is Erythema Nodosum treated?
Treatment focuses on finding and addressing the cause, together with resting the legs, keeping them elevated, and taking NSAIDs as prescribed by a doctor. In severe cases, potassium iodide or oral steroids may be used once it is certain there is no infection.
If you have painful red lumps on your shins, especially on both sides, together with fever or joint pain, see a doctor to look for a hidden cause. Consult a dermatologist at Siam Dermatology, call +66 61 448 7000 or LINE @siamderm.
Written by Dr. Patara Voravutinon, Dermatologist · Last reviewed August 22, 2026
Comments