Common dog skin lumps in UK dogs: lipoma, cyst, wart, mast cell explained

Once you've found a lump on your dog and decided whether it's a same-day vet call or a routine appointment (covered in our when to worry guide), the natural next question is: what could it actually be?

This is the UK guide to the lump types vets see most often in first-opinion practice. We cover what each one usually looks and feels like, the breeds at higher risk, how UK vets diagnose them, and what treatment usually involves. Important caveat up front: you cannot reliably diagnose a lump by feel, including from this guide. Use it for orientation, not for self-diagnosis.

Lipoma — the most common

What it usually feels like: soft, doughy, freely movable under the skin (think marble in a stocking). Slow-growing over months. Most often on the trunk, armpits, or chest of middle-aged to older dogs.

Higher-risk UK breeds: Labradors, Cocker Spaniels, Dachshunds, Doberman Pinschers, Weimaraners.

What UK vets do: fine-needle aspirate (FNA) to confirm. Cytology shows fat cells. If confirmed, most lipomas are monitored rather than removed unless they're growing fast, in an awkward location (under the armpit affecting movement, near a joint, on the eyelid), or causing the dog discomfort.

The catch: some “lipomas” turn out to be infiltrative lipomas or liposarcomas, which are aggressive. FNA confirmation matters — even though the lump feels classic.

Sebaceous cyst

What it usually feels like: small (5–20mm), firm, dome-shaped, often under the skin on the back, neck, or head. Sometimes ruptures and weeps a thick, cheesy, foul-smelling material. May resolve and recur in the same spot.

Higher-risk UK breeds: Schnauzers, Spaniels, Yorkshire Terriers, Poodles.

What UK vets do: visual inspection plus FNA if there's any uncertainty. Most sebaceous cysts are left alone unless they keep rupturing, becoming infected, or are in a high-friction location.

Don't squeeze it at home. Squeezing risks rupture into surrounding tissue, infection, and scarring.

Histiocytoma — the “button tumour”

What it usually feels like: small (typically <2cm), firm, raised, button-shaped, often pink or red, sometimes ulcerated. Fast-growing — appears within weeks. Almost exclusively in young dogs under 3 years.

Higher-risk UK breeds: Boxers, English Bulldogs, Great Danes, Scottish Terriers.

What UK vets do: FNA confirms histiocytoma cells. Most regress spontaneously within 2–3 months without treatment. Watchful waiting is the usual approach.

The catch: the fast growth can feel alarming and looks similar to mast cell tumours on visual exam. FNA is essential to tell them apart.

Wart (papilloma)

What it usually looks like: cauliflower-textured growth, often on the lips, mouth, eyelids, or face. Can occur singly or in clusters. Caused by canine papillomavirus.

Most common in: young dogs under 2 (immune system still developing) and older dogs (immune system declining).

What UK vets do: visual diagnosis is usually enough. Most warts resolve on their own within 1–5 months as the dog's immune system clears the virus. Removal is offered if they're interfering with eating, getting traumatised, or persisting.

Mast cell tumour — “the great pretender”

What it can look like: almost anything. The reason UK vets call it the great pretender is that mast cell tumours can look like insect bites, lipomas, ulcers, or unremarkable raised lumps. Often itchy. May change in size from day to day — release of histamine causes intermittent swelling.

Higher-risk UK breeds: Boxers, English Bulldogs, Boston Terriers, Pugs, Labradors, Golden Retrievers, Pit Bulls, Sharpeis.

What UK vets do: FNA is essential and almost always diagnostic. Mast cell tumours are graded I, II, or III by histopathology after surgical removal, and staging may include lymph node FNA, spleen and liver scan, and chest x-rays.

This is the lump UK vets most commonly miss when not aspirated. If you take one thing from this article, it's that any new lump on a high-risk breed deserves an FNA, even if it looks innocent.

Soft tissue sarcoma

What it usually feels like: firm, often anchored to deeper tissue (doesn't roll under the skin like a lipoma), slow-growing but locally aggressive. Most common on the limbs.

Higher-risk UK breeds: larger breeds, middle-aged to older.

What UK vets do: FNA may suggest the diagnosis but biopsy is usually needed for confirmation and grading. Treatment is surgical removal with wide margins; some types need radiation follow-up.

Mammary tumour

What it usually feels like: a firm lump along the mammary chain (the row of nipples down the belly) in unspayed or late-spayed female dogs.

The critical point: roughly 50% of canine mammary tumours are malignant. Do not wait. UK vets recommend prompt surgical removal of any mammary lump, with histology to determine if further treatment is needed.

Spaying before the first season eliminates this risk almost entirely; spaying after several seasons provides much less protection.

Skin tag (acrochordon)

What it looks like: small, soft, pedunculated (on a stalk) growth, often skin-coloured. Common in older dogs.

What UK vets do: visual diagnosis is usually enough. No treatment needed unless they're getting caught and bleeding.

Abscess

Not strictly a lump in the tumour sense, but worth covering because it presents the same way to owners. Sudden onset of a hot, painful, often soft swelling, sometimes with visible puncture wound. The dog may be lethargic and off food. Most commonly results from a bite (other dog, cat, fox) or a foreign body.

Same-day vet call. Abscesses often need lancing, flushing, and antibiotics.

How daily nutritional support fits in

Skin and immune health are part of overall wellness. Super Everyday is Superwild's vet-developed daily powder, designed to support the seven pillars of canine wellness, including skin barrier and immune resilience, across the lifespan. It is not a treatment for any lump and does not prevent or shrink tumours.

Frequently asked questions

What is the most common lump on dogs in the UK?

Lipomas are the single most common lump UK vets diagnose, particularly in middle-aged to older Labradors, Cocker Spaniels, and Dachshunds. They feel soft, doughy, and freely movable under the skin. Despite being almost always benign, fine-needle aspirate (FNA) confirmation is recommended because some lipomas turn out to be infiltrative or liposarcomas.

How can I tell the difference between a lipoma and a mast cell tumour?

You cannot reliably tell them apart by feel — UK vets cannot either. Mast cell tumours are called “the great pretender” because they can look like lipomas, insect bites, ulcers, or unremarkable raised lumps. The only reliable way to differentiate is fine-needle aspirate (FNA), which is quick, cheap, and in-clinic.

What does a histiocytoma look like on a dog?

A histiocytoma is typically a small (under 2cm), firm, raised, button-shaped lump, often pink or red, sometimes ulcerated. They appear suddenly and grow fast over weeks, almost always in dogs under 3 years old. Most regress spontaneously within 2–3 months. FNA is needed to confirm because they can mimic mast cell tumours.

Should I have my dog's lipoma removed?

Most UK vets monitor confirmed lipomas rather than remove them. Removal is recommended if the lipoma is growing fast, in an awkward location (affecting movement, near a joint, on the eyelid), causing the dog discomfort, or if cytology suggests it might be infiltrative. Anaesthesia carries risk; the lipoma usually doesn't.

Are warts on dogs contagious?

Yes — canine papillomavirus is contagious between dogs, particularly young dogs in social settings (kennels, dog parks, training classes). It is not contagious to humans or other species. Warts usually resolve on their own within 1–5 months as the dog's immune system clears the virus.

Last updated April 2026. This guide is intended for general information and does not replace advice from a UK-registered MRCVS veterinarian. Any new lump warrants veterinary assessment.