Monitor — routine vet appointment

Lump on a cat's skin

Check the lump's size, location, and texture, then book a vet appointment — any lump at a vaccination site that persists beyond 4 weeks or grows must be seen urgently.

Cat

In the next 60 seconds

Stay calm and handle your cat gently — a painful abscess can cause a cat to bite or scratch.
Examine the lump carefully without squeezing or pressing hard. Note its size (pea, grape, golf-ball?), texture (soft/fluctuant vs hard/firm), location, and whether the overlying skin is broken.
If the lump is at or near a previous vaccination site (commonly between the shoulder blades or on a limb), note exactly how long it has been there.
Do not attempt to lance, burst, or squeeze the lump — this risks spreading infection or damaging underlying tissue.
If the lump is warm, painful, and fluctuant (feels fluid-filled), apply a warm (not hot) compress with a clean cloth for a few minutes to soothe discomfort, but do not delay seeing a vet.
Keep the area clean and dry. If the lump is already discharging, cover loosely with a clean gauze pad to prevent contamination.
Book a vet appointment. For most lumps, a non-urgent appointment within a few days is appropriate — but see below for red flags requiring urgent attention.
Photograph the lump at regular intervals so your vet can assess change over time if needed.

Recognise the signs

A new, palpable swelling under or within the skin
Lump is warm, painful, or fluctuant — suggests abscess or haematoma
Hard, fixed, irregular, or rapidly growing lump — raises concern for malignancy
Lump located between the shoulder blades or at another previous injection site
Discharge of pus, blood, or malodorous fluid from the lump or a nearby wound
Multiple lumps along the belly in a female or unspayed cat — possible mammary tumours
Cat grooming, scratching, or appearing uncomfortable around the lump
Weight loss, lethargy, or reduced appetite alongside the lump

First aid steps

Stay calm and handle your cat gently — a painful abscess can cause a cat to bite or scratch.
Examine the lump carefully without squeezing or pressing hard. Note its size (pea, grape, golf-ball?), texture (soft/fluctuant vs hard/firm), location, and whether the overlying skin is broken.
If the lump is at or near a previous vaccination site (commonly between the shoulder blades or on a limb), note exactly how long it has been there.
Do not attempt to lance, burst, or squeeze the lump — this risks spreading infection or damaging underlying tissue.
If the lump is warm, painful, and fluctuant (feels fluid-filled), apply a warm (not hot) compress with a clean cloth for a few minutes to soothe discomfort, but do not delay seeing a vet.
Keep the area clean and dry. If the lump is already discharging, cover loosely with a clean gauze pad to prevent contamination.
Book a vet appointment. For most lumps, a non-urgent appointment within a few days is appropriate — but see below for red flags requiring urgent attention.
Photograph the lump at regular intervals so your vet can assess change over time if needed.

Do NOT

Do NOT squeeze, pop, or lance the lump at home — you risk spreading infection or causing serious injury.
Do NOT apply human antiseptic creams (e.g. Savlon, TCP) directly — many are toxic to cats if licked.
Do NOT delay if the lump is at a vaccination or injection site and has been present for more than 4 weeks or is growing — this is a specific red flag for injection-site sarcoma (ISS).
Do NOT assume any lump is harmless just because it is soft or your cat seems unbothered — mast cell tumours and early ISS may be painless.
Do NOT give your cat paracetamol (acetaminophen) or ibuprofen for pain — both are fatal to cats.

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When to phone the vet immediately

Any lump at a previous vaccination or injection site that has been present for more than 4 weeks — ISS must be ruled out with urgent biopsy
A lump that doubles in size over 2–4 weeks
A hard, irregular, or fixed lump (does not move freely under the skin)
Discharge of pus or blood from the lump, or a foul smell
Multiple lumps along the mammary chain (belly) of a female cat — veterinary assessment same day
Cat is feverish, off food, lethargic, or hiding
Signs of systemic illness alongside any lump

When it can usually wait

A small, soft, freely moveable lump that has been present and unchanged for several weeks in an otherwise well cat — book a routine vet appointment within 1–2 weeks
Soft, fluctuant lump that appears a few days after a known injury or bite wound, with no fever and no general illness — still needs vet attention but not same-day

Common causes

Abscess from a bite wound (the most common cause of a skin lump in cats)
Sebaceous or epidermal cyst (fluid or keratin-filled)
Swollen lymph node (reactive or due to infection, immune disease, or cancer)
Mammary tumour (cats have a very high malignancy rate — around 85–90%)
Mast cell tumour (more common in cats than many owners realise — can appear anywhere on skin)
Injection-site sarcoma (ISS) — a rare but aggressive tumour at a previous vaccination or injection site
Lipoma (benign fatty lump — rare in cats, unlike in dogs)
Haematoma (blood blister from trauma or self-trauma)

What you'll need

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What the vet will need to know

When did you first notice the lump?
Has it changed in size, shape, or texture?
Has your cat had any recent bite wounds, fights, or injections at that location?
Is the lump painful when touched?
Has your cat had any previous lumps or medical conditions?
Is the cat eating, drinking, and toileting normally?
When was the cat last vaccinated and where was the injection given?

Aftercare

If the vet has drained an abscess: keep the wound clean as directed, complete the full course of antibiotics, and return for follow-up.
If a biopsy or fine needle aspirate (FNA) has been performed: await results before assuming the lump is benign.
If ISS is confirmed: your vet will refer to a specialist oncologist — surgery with wide margins, radiation therapy, and/or chemotherapy may be recommended. Act quickly as ISS grows aggressively.
If a mammary tumour is removed: discuss spaying if not already done, as oestrogen drives mammary tumour growth in cats.
Monitor the removal site for recurrence and attend all follow-up appointments.

Prevention

Keep cats indoors or in a secure garden to reduce bite-wound abscesses from cat fights.
Neuter male cats to reduce territorial fighting.
Spay female cats before their first season — dramatically reduces mammary tumour risk.
Attend regular vet check-ups so lumps are found early.
Record each vaccination site on your cat's health record — this helps monitor for ISS.
Vaccinations can now be given in the leg (rather than between the shoulder blades) to allow easier surgical removal if ISS develops — discuss with your vet.

Breed-specific notes

Siamese cats have an increased risk of mammary tumours.
Older domestic shorthair cats are at increased risk of mast cell tumours.
No breed is exempt from ISS — it is a risk for any cat receiving injections.

Frequently asked questions

What is injection-site sarcoma (ISS) in cats?

ISS is a rare but aggressive cancer that develops at the site of a previous injection (most commonly vaccines). Any lump between the shoulder blades — or at any injection site — that is present for more than 4 weeks, is larger than 2 cm, or is growing must be biopsied urgently. Early, wide surgical removal gives the best prognosis. If caught late, ISS has a poor outlook.

My cat has a soft lump on its neck. Is it dangerous?

Soft lumps are often abscesses, cysts, or reactive lymph nodes — but softness alone does not confirm benign disease. Any new lump should be assessed by a vet. If the lump is at an injection site, it must be evaluated promptly regardless of its consistency.

Can cats get lipomas like dogs?

Lipomas (benign fatty lumps) are much less common in cats than in dogs. A fatty-feeling lump in a cat is statistically more likely to be something else — including a mast cell tumour or ISS — so all lumps in cats should be checked by a vet rather than assumed to be harmless lipomas.

How are skin lumps diagnosed?

Your vet may perform a fine needle aspirate (FNA) — inserting a small needle to collect cells for analysis — or recommend a biopsy for a larger tissue sample. Both can usually be done under light sedation or local anaesthetic. Imaging (ultrasound or X-ray) may also be used to check for spread.

Are mammary lumps in cats always cancer?

Approximately 85–90% of mammary tumours in cats are malignant, which is far higher than in dogs. Any lump along the mammary chain should be assessed as a priority. Spaying before the first season greatly reduces risk — spaying after two seasons provides much less protection.

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