Medically reviewed guide · Last updated: 13 November 2026 · Reading time: approx. 10 min

Lump Under the Skin: Lipoma, Cyst or Something More?

The most common causes compared

The causes in detail

A lump under the skin is often noticed by chance — while showering, applying cream or shaving. The first question is: where is it? If it is on the neck, in the armpit or in the groin, a lymph node is the most likely explanation; how to make sense of enlarged lymph nodes is described in detail in our article on swollen lymph nodes. This article is about the other lumps: in the skin, in the fatty tissue beneath it and at the joints. Lumps in the breast have their own article: breast lump.

Lipoma: the soft fatty lump

Lipomas are benign growths of fatty tissue and are among the most common lumps of all. They feel soft to doughy, move easily under the skin, usually do not hurt and grow very slowly, if at all. Some people have several, and they sometimes run in families. Small, slightly tender variants containing blood vessels (angiolipomas) often occur in multiples on the arms and trunk. First step: a typical small lipoma does not need to be removed. If it is larger than about 5 cm, is noticeably growing, lies deep beneath the muscle sheath or its nature is uncertain, an ultrasound follows — very rarely, such a finding turns out to be a malignant fatty tissue tumour (liposarcoma).

Skin cyst: the lump with a dot

An epidermoid cyst — colloquially often called a “sebaceous cyst” — is a cavity in the skin filled with keratin. It is firm, round, attached to the skin and often has a small dark dot in the centre. Similar cysts (trichilemmal or pilar cysts) are common on the scalp. Cysts can become inflamed; they then turn red and painful and can burst. First step: do not squeeze it — that pushes the inflammation into the tissue. If the cyst bothers you, it is removed together with its capsule while it is not inflamed; otherwise it often grows back. An acutely inflamed cyst is drained first.

Abscess and boil

A boil (furuncle) is a pus-filled infection of a hair follicle, usually caused by staphylococci; several boils that merge are called a carbuncle. An abscess is an encapsulated collection of pus in the tissue. Both are red, hot and painful and later become soft in the centre. Risk factors are diabetes, excess weight, shaving and a weakened immune system. Recurring painful lumps and sinus tracts in the armpits and groin can point to hidradenitis suppurativa (acne inversa), a chronic inflammatory skin disease that should be treated by a specialist. First step: small boils often heal with warm compresses; a larger abscess must be opened by a doctor. If the redness spreads over a wider area or fever develops, erysipelas or a deeper infection may be behind it.

Ganglion, hernia and lumps at the joints

A ganglion (“ganglion cyst”) is a bulge filled with joint fluid, typically on the back of the hand or on the inner side of the wrist. It is firm-elastic, sits firmly in place and can go away on its own. A lump in the groin or at the navel that gets bigger when you cough or strain and can be pushed back when lying down suggests a hernia — more under inguinal hernia. Firm, painless lumps on the outer side of the elbows or on the fingers can be rheumatoid nodules in rheumatoid arthritis; yellowish-white lumps on the ear, fingers or elbows point to uric acid deposits (gouty tophi) in long-standing gout.

Small hard skin nodules

A hard, brownish nodule the size of a lentil, often on the legs, is frequently a dermatofibroma — a harmless overgrowth of connective tissue, for example after an insect bite. Typically, if you pinch the skin together from the sides, the nodule dimples in the centre. New, growing, shiny, bleeding or dark nodules, on the other hand, should be looked at by a dermatologist, because non-melanoma skin cancer and nodular forms of melanoma sometimes also start as an inconspicuous lump.

Red, painful lumps on the shins

Several coin-sized, red to bluish, tender lumps on both lower legs are typical of erythema nodosum, an inflammation of the fatty tissue under the skin. It is the body’s reaction to something else: infections, for example with streptococci, inflammatory bowel diseases such as Crohn’s disease, sarcoidosis, pregnancy or medicines. It usually heals within a few weeks, but a doctor should look for the cause.

Rare but important: malignant lumps

Malignant soft tissue tumours (sarcomas) are rare. They usually grow painlessly, become larger than 5 cm, feel firm and often lie deep beneath the muscle sheath. Hard lymph nodes that cannot be moved can point to lymphoma or to spread from another cancer, especially together with fever, night sweats and unintentional weight loss. This combination is the reason why a new lump that does not fit the harmless patterns should be examined.

Self-checks: first clues at home

These observations replace neither a medical examination nor a diagnosis. They help you describe the lump and notice changes.

• Document the size: Place a ruler or a coin next to it, take a photo and note the date. Repeat this after two and after four weeks — growth is one of the most important criteria.
• Mobility: Can the lump be moved back and forth under the skin, or is it fixed to the tissue beneath? If it moves with the skin, that suggests a skin cyst.
• Consistency: soft and doughy (more likely a lipoma), firm-elastic (more likely a cyst or ganglion) or as hard as a pebble (get it checked)?
• The dot in the centre: A small dark dot on top suggests an epidermoid cyst.
• The cough test: If a lump in the groin or at the navel gets bigger when you cough, a hernia is likely.
• Signs of inflammation: Redness, warmth, pain and fever suggest an infection. Trace the edge of any redness with a pen — if it spreads within hours, it is urgent.
• Injection site check: Do you inject insulin, heparin or other medicines under the skin? Feel the injection areas — rubbery pads are a sign of changes in the fatty tissue.

Warning signs: when you should not wait

• A lump that is larger than about 5 cm or noticeably grows within weeks
• A hard, irregular lump firmly attached to the tissue beneath
• A lump that lies deep beneath the muscle sheath or comes back after removal
• A lymph node larger than about 2 cm, or one that stays enlarged for more than about four weeks without an obvious infection
• Lumps together with fever, night sweats or unintentional weight loss
• A new, growing, bleeding or dark skin nodule
• Redness that spreads rapidly, with fever, chills or severe pain
• A painful hernia in the groin or navel that can no longer be pushed back, with nausea or vomiting

The treatment pathway: step by step

1. Watch it, if appropriate. A small, soft, mobile lump without symptoms, or a lymph node during an infection, can be watched for a few weeks — with a photo and a tape measure.
2. Examination at the GP practice. The practice feels the lump, asks about how long it has been there, growth and accompanying symptoms, and can order blood tests if needed. Bring your photos and a list of your medicines.
3. Ultrasound. It shows whether the lump is fluid-filled or solid, how deep it lies and whether it has a blood supply — the most important examination for most lumps under the skin.
4. Specialist, if needed. Dermatology for skin nodules, surgery for bothersome lipomas, cysts or hernias, orthopaedics or hand surgery for a ganglion, rheumatology for rheumatoid or gout nodules. For unclear, large or deep lumps, MRI and a tissue sample follow, ideally at a specialised centre before any operation.
5. Treatment according to the cause. Lipomas and cysts are removed under local anaesthetic if they cause problems, abscesses are opened, ganglia are only operated on if they cause problems, and hernias are operated on depending on the findings. Antibiotics are not always needed for an abscess — the decision lies with the treating practice.

The medication angle: when injections and tablets cause lumps

An underestimated share of lumps under the skin has to do with medicines — above all with those injected under the skin.

Insulin: fatty lumps at the injection site

If you always inject insulin in the same place, rubbery pads of fatty tissue (lipohypertrophy) often form there. They are harmless but treacherous: insulin is absorbed unreliably there, blood sugar levels fluctuate, and more insulin is often needed. If you then switch to healthy skin, the same dose may cause low blood sugar — so discuss the dose and the change of site with the practice. Less often, the insulin itself is deposited as firm lumps. How to rotate injection sites properly is shown in our guide Injecting insulin correctly.

Heparin, weight-loss injections and biologics

After heparin injections such as enoxaparin, small bruises and hardened areas often remain and recede over days to weeks. GLP-1 medicines such as semaglutide and biologics such as adalimumab can also cause injection site reactions with redness and hardening. After vaccinations, a small, hard lump can remain palpable at the injection site for a few weeks. If an injection site becomes increasingly red, hot and painful, that is a reason to see a doctor.

Blood thinners

On anticoagulants such as apixaban, rivaroxaban or phenprocoumon and on antiplatelet drugs, even minor knocks can cause palpable bruises that feel like lumps. They usually become softer and smaller within weeks. Large, growing or very painful swellings should be looked at by a doctor. Even so, do not stop the blood thinner on your own — tips are in our guide Living with blood thinners.

Tablets as triggers

Hormonal contraceptives such as the pill and some antibiotics are among the described triggers of erythema nodosum. Cortisone injections can leave a dent at the injection site due to loss of fatty tissue. Whether a medicine is the cause is for the practice to decide — do not stop it, but document the timing.

Painkillers for inflamed lumps

For a painful boil or erythema nodosum, ibuprofen or paracetamol can help in the short term. According to the package leaflet, over-the-counter painkillers should generally not be taken for more than three to four days in a row without medical advice. Painkillers do not make an abscess better — it needs to be treated.

How to help prevent lumps under the skin

Lipomas and most cysts cannot be specifically prevented. With inflammatory lumps and injection sites, however, there is quite a lot you can do:

• Rotate injection sites systematically — abdomen, thighs, buttocks in a fixed pattern, each injection at least a few centimetres from the last one, and do not reuse needles.
• Shave gently — a sharp blade, in the direction of hair growth, not over inflamed areas; this lowers the risk of boils in the armpit and groin.
• Keep blood sugar well controlled — with diabetes, skin infections heal less well and come back more often.
• Do not squeeze — leave cysts, spots and boils alone, and they will become inflamed less often.
• Check your skin regularly — feel your body and look at your moles once a month, and from age 35 use the skin cancer screening every two years that is covered by statutory health insurance.

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