Finding a lump on your dog is alarming, and the reassuring truth is that most are benign — particularly in older dogs, where fatty lumps are extremely common.
The unreassuring truth is that you cannot tell by feel, and neither can your vet. Appearance and texture are not reliable indicators. The only way to know is to sample it.
The common benign ones
Lipoma. Soft, movable fatty lumps under the skin, usually on the chest, belly or legs. Very common in middle-aged and older dogs, especially overweight ones. Usually left alone unless they interfere with movement.
Sebaceous cyst. A blocked gland. Firm, sometimes discharging a thick white material. Can become inflamed.
Histiocytoma. A small, raised, hairless red button, usually on a young dog’s head, ear or leg. Appears quickly and often regresses on its own within a few months. Genuinely benign.
Wart (papilloma). Cauliflower-textured, often around the mouth in young dogs, caused by a virus. Usually resolves.
Skin tag. Small, soft, stalked. Harmless.
Abscess. Hot, painful, rapidly appearing swelling, often after a bite or a puncture. Needs treatment, not observation.
The ones that matter
Mast cell tumour. The great imitator. Can look like anything — a wart, a lipoma, a small pink lump, an insect bite. May change size from week to week, and sometimes becomes red and swollen after being handled, because the cells release histamine.
This is the single best argument for having every lump checked. Mast cell tumours are common, they are variable, and they are treatable when caught early.
Soft tissue sarcoma. Firm, often deep, slow-growing, frequently on a limb or the trunk.
Melanoma. Pigmented lumps, particularly in the mouth or on the toes. Oral melanoma is aggressive.
Squamous cell carcinoma. Often on unpigmented, sun-exposed skin, or on the toes.
Lymphoma. Not a skin lump but frequently found as enlarged lymph nodes — under the jaw, in front of the shoulders, behind the knees. If you find firm swellings in several of these places at once, go the same week.
Mammary tumours. Along the chain of mammary glands, most common in unspayed or late-spayed females. Roughly half are malignant.
Testicular tumours in entire males — any change in size or firmness of one testicle.
Go to the vet promptly if a lump
- Is growing, especially quickly
- Has changed in size, shape, colour or texture
- Is firmly attached to underlying tissue
- Is ulcerated, bleeding or discharging
- Is painful, or the dog licks at it persistently
- Is on the toes, in the mouth, on the eyelid, or near the anus — these locations carry a higher risk
- Appears alongside weight loss, lethargy or reduced appetite
- Is one of several appearing at once
- Involves swollen lymph nodes
And as a general rule: any new lump in a dog over seven is worth a check, and any lump you are thinking about is worth a check. There is no prize for waiting.
The test that gives the answer
Fine needle aspirate. A small needle is used to draw cells from the lump, which are examined under a microscope. Usually done conscious, in a consultation, takes a minute, and costs relatively little.
This is the test that matters, and it is why “let’s monitor it” without sampling is an incomplete answer for anything new.
Biopsy removes a piece or the whole lump for full examination, giving a definitive diagnosis and information about margins. Needed when an aspirate is inconclusive, or when the lump is being removed anyway.
Occasionally an aspirate is not diagnostic — some tumour types do not shed cells easily — and a biopsy follows.
Monitoring properly
If you and your vet decide to monitor a known benign lump, do it with records rather than impressions.
- Measure it with a ruler or calipers, in two dimensions
- Photograph it beside a coin or a ruler for scale
- Write the date
- Map it. Draw a rough outline of your dog and mark each lump with a number. In a dog with multiple lipomas this is the only way to notice that one of them has changed
- Recheck monthly
A lump that has been identical for two years is very different from one that appeared last month.
The monthly check
Two minutes, once a month, ideally while your dog is relaxed:
- Run both hands over the whole body, including the head, ears and muzzle
- Down each leg, between the toes, and over the pads
- Along the belly and the mammary chain
- Around the tail base and the anal area
- Lift the lips and look at the gums and inside the mouth
- Feel the lymph nodes: under the jaw, in front of the shoulders, behind the knees
Dogs generally enjoy it, and it doubles as handling practice that makes vet visits easier.
Do not
- Squeeze, pop or drain a lump. You can rupture a mass, spread cells, or introduce infection
- Apply home remedies — black salve and similar products cause severe tissue damage and are genuinely dangerous
- Assume a soft lump is a lipoma. Some sarcomas are soft
- Wait to see if it grows before booking, unless your vet has already sampled it and advised that
The realistic picture
Most lumps turn out to be nothing. The cost of checking is a consultation and an aspirate. The cost of not checking, in the minority of cases where it matters, is a tumour that was removable in March and difficult in September.
That asymmetry is the whole argument.
