Lumps & Bumps
Finding a lump on your cat can be an alarming moment. The good news is that the majority of lumps and bumps in cats turn out to be harmless — but the important thing is that you can't tell which is which just by looking or feeling. The only way to know what you're dealing with is to have it checked by your vet. The sooner that happens, the better the outcome if it does turn out to be something that needs treatment — and the sooner you can stop worrying if it doesn't.
The Golden Rule — Get It Checked
No matter what a lump looks like, feels like, or where it is, the rule is always the same: new lump, see your vet. Not eventually — within a few days.
This isn't about causing unnecessary alarm. Most lumps are benign. But you genuinely cannot tell a harmless cyst from a tumour by touching it — and neither can your vet without proper investigation. What you can do is give your cat the best possible chance by catching anything concerning early, before it has time to develop. A lump that's easy to remove at a small size can become much harder to treat if left to grow.
Get into the habit of running your hands gently over your cat's whole body during grooming sessions. Cats with thicker or longer coats can hide lumps particularly well, so feel as well as look. If you find something new — even something small — note when you found it, where it is, and book a vet appointment.
Common Benign Causes
Many lumps in cats are completely harmless. Some of the most frequently seen include:
Abscesses are one of the most common causes of sudden lumps, particularly in outdoor cats. They develop when bacteria get under the skin — most often from a bite wound sustained in a cat fight. Abscesses are painful, feel warm to the touch, and may have a small puncture mark at the centre. They can grow surprisingly quickly and sometimes burst, releasing pus. Your vet will need to drain and clean the wound and will usually prescribe antibiotics. Cat bites are notorious for causing infection because of the bacteria in a cat's mouth, so always get a suspected bite wound checked promptly rather than waiting to see if it settles.
Cysts are fluid-filled or keratin-filled sacs that form just under or within the skin. They're typically round, firm, and smooth, and may be present for months or years without causing any problems. They can occasionally become infected or burst. Most are left alone unless they're causing discomfort or repeatedly becoming inflamed.
Lipomas are soft, slow-growing fatty lumps that sit just under the skin and move freely when you press them. They're more common in older or overweight cats. Lipomas are generally harmless and don't usually need treatment unless they grow large enough to cause problems.
Skin tags and warts are small, fleshy benign growths that become more common with age. They rarely cause any issue for the cat, though your vet will want to confirm that's what they are.
Post-vaccination swellings can occur in the days following an injection and are usually a normal, temporary response. A small, firm lump at the injection site that reduces and disappears within a few weeks is generally nothing to worry about — but see below for important information about lumps that persist.
Injection Site Lumps — What You Need to Know
This is something every cat owner should be aware of.
In a small number of cats, a lump at a vaccination or injection site doesn't resolve as expected — and in rare cases, this can be the first sign of a condition called Feline Injection Site Sarcoma (FISS), an aggressive form of cancer that can develop at the site of a previous injection.
The risk is rare — estimated at somewhere between 1 in 1,000 and 1 in 10,000 injected cats — but because FISS can be serious, any lump at an injection site that doesn't behave as expected needs prompt attention. Vets use what's called the 3-2-1 rule as a guide:
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See your vet if a lump at an injection site is still present 3 months after the injection
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See your vet immediately if the lump is larger than 2 cm in diameter
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See your vet if the lump has been growing for 1 month after you first noticed it
If any of these apply, your vet will investigate further. It's important to be clear that the risk of the diseases prevented by vaccination far outweighs the very small risk of injection site reactions — this information is not a reason to avoid vaccinating your cat. But it is a reason to monitor injection sites after vaccination and act promptly if something doesn't resolve.
When Lumps Are More Serious
Some lumps are malignant — meaning they're cancerous and have the potential to spread. These can look and feel identical to benign lumps from the outside, which is exactly why vet assessment matters so much.
Some of the more common cancerous lumps seen in cats include:
Mast cell tumours can appear anywhere on the skin and vary widely in appearance — some look like small raised bumps, others are flat or ulcerated. They can behave unpredictably, sometimes growing slowly for months before suddenly changing. Mast cell tumours are usually surgically removed and often have a good outcome when caught and treated early.
Squamous cell carcinoma is more common in white or pale-coloured cats, and most often appears on sun-exposed areas — the ears, nose, and eyelids. It can start as a crusty, reddened area that doesn't heal, progressing to an open sore. Sun protection and keeping at-risk cats out of direct sun during peak hours can reduce the risk.
Mammary tumours are relatively common in unspayed female cats, and unfortunately are more likely to be malignant in cats than in dogs. Any lump near the mammary glands — which run in two rows along the underside of the abdomen — should be checked promptly. Spaying before the first season significantly reduces the risk.
What Your Vet Will Do
When you bring your cat in with a lump, your vet will examine it carefully — noting its size, shape, texture, location, and how it behaves when pressed. They'll check whether it's freely moveable or fixed to underlying tissue, and whether there are other lumps elsewhere.
Depending on what they find, they may recommend a fine needle aspirate (FNA) — a quick, minimally invasive procedure where a tiny needle is used to draw out a sample of cells for examination. This can often be done during the appointment without sedation. An FNA gives useful information but isn't always conclusive, and a biopsy — removing a small sample of tissue for laboratory analysis — may be needed to get a definitive answer.
If a lump needs to be removed, your vet will discuss the best approach. For some lumps this is a straightforward procedure; others require wider surgical margins or referral to a specialist, depending on the type and location.
When To Act Quickly
Most lumps warrant a prompt appointment rather than an emergency visit — but there are situations where you should contact your vet the same day:
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A lump has appeared very suddenly and is growing rapidly
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The lump is warm, painful, or your cat is distressed when it's touched
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There is any discharge, bleeding, or open skin over the lump
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Your cat is unwell in other ways alongside the lump — off food, lethargic, or hiding
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A lump at a previous injection site is still present three months later, growing, or larger than 2cm
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Any lump near the mammary glands in an unspayed female cat
When in doubt, always call your vet and describe what you've found. A quick phone conversation will tell you how urgently your cat needs to be seen — and finding something early is always better than waiting.