You're stroking your cat and your fingers stop on something that wasn't there last week: a small, firm bump, or a soft swelling that seems to have appeared overnight. The first word most people reach for is "cyst".
Sometimes that's right. But in cats, a true cyst is often not the most likely explanation. A lump that pops up quickly on a cat that goes outside is often an abscess from a bite. Others turn out to be inflamed skin, an oil gland problem, a tick, a nipple, or a tumor. Several of these look and feel almost the same, and no one can tell them apart by touch. So the plan is the same for every new lump: don't squeeze it, and have your vet check it, usually with a quick needle sample.
What Is a Cat Cyst?
A cyst is a closed sac in or under the skin with its own lining, which fills the sac with fluid or a semisolid material. Cysts are benign: they don't spread. The trouble is that they can look a lot like lumps that do.
Cats get two main kinds:
- Keratin-filled (follicular) cysts. Most form from a malformed hair follicle and fill with keratin, the tough protein in the outer layer of skin. They feel like a lump with a hard or solid core and may be the same color as the surrounding hair. According to the Merck Veterinary Manual, they're only occasionally found in cats.
- Sweat gland (apocrine) cysts. These show up in middle-aged and older cats, most often on the head and neck, as fluid-filled lumps or small blisters. In cats the fluid inside can be dark, so a cyst on the ear can look like a pigmented tumor.
A rarer relative is the dilated pore of Winer, a growth seen in senior cats, usually on the head. It looks like one very large blackhead and is benign.
Surgical removal is the usual treatment for both kinds. Merck notes that removing a sweat gland cyst completely cures it.
Two Common "Cysts" That Aren't Cysts
Feline acne shows up as blackheads (comedones) on the chin and lips. It's usually cosmetic, but the spots can become infected and sore. Popping them makes things worse. Our guide on treating cat acne covers it in more detail.
Stud tail (tail gland hyperplasia) is an overgrowth of the oil glands on the top of the tail near its base. You may see a patch of hair loss, greasy fur, blackheads or crusts, and sometimes an infection. Testosterone is the most common driver, so it's most often seen in intact males, although any cat can get it. Neutering can help stop it from getting worse, and your vet may also look for anything that makes it hard for your cat to groom.
Other Lumps and Bumps on Cats
Abscesses
An abscess is a pocket of pus under the skin. One of the most common causes in cats is a bite from another animal, which carries bacteria under the skin, so cats that go outside or get into fights are at higher risk.
An abscess usually appears suddenly as a painful swelling that may feel firm or squishy, like a water balloon. Many cats also run a fever, seem tired, or go off their food. Some abscesses burst, leaving a raw wound and a thick, foul-smelling discharge.
Abscesses aren't cancerous, but they need a vet: the pus has to come out, and your vet decides on antibiotics and pain relief. Keeping your cat indoors lowers the risk of fight wounds (we weigh up indoor vs outdoor cats separately).
Eosinophilic granuloma complex
Eosinophilic granuloma complex is a group of inflammatory skin lesions driven by eosinophils, a type of white blood cell. It usually traces back to an allergy, often to flea or other insect bites. It can show up as raised, yellowish to pink bumps (often on the back of the thighs, the chin or the lips), as red, very itchy plaques on the belly or thighs, or as a sore on the upper lip, the so-called rodent ulcer. A Cornell veterinary dermatologist describes some lesions as "big tumor-like bumps", which is why they need a proper diagnosis.
Tumors
Benign tumors stay put; malignant (cancerous) ones can invade nearby tissue and spread. Only a sample examined under a microscope tells them apart, and that matters more in cats than many owners expect. Veterinary oncologist Dr. Sue Ettinger, writing in Today's Veterinary Practice, notes that four tumor types (basal cell tumors, mast cell tumors, squamous cell carcinomas and fibrosarcomas) make up about 70% of skin tumors in cats, and that once basal cell tumors are left out, studies report 70% to 80% of feline skin tumors are malignant. Those figures come from tumors that were sampled, not from every lump on every cat, but they're a good reason not to assume.
A few names you may hear from your vet:
- Basal cell tumors are common in older cats: firm, often dark, and able to form cysts, so they can pass for one. They're benign.
- Mast cell tumors are the second most common skin tumor in cats, usually a single hairless lump on the head or neck. Most behave benignly in cats, but some come back after surgery or spread.
- Lipomas (soft fatty lumps) are only occasionally seen in cats, and Merck advises against ignoring them, because only testing separates them from rarer cancerous fatty tumors.
- Squamous cell carcinoma often starts as a sore that won't heal on the ears, nose or eyelids of cats with white fur there. Sun exposure is a major cause.
Lumps where your cat was vaccinated
Rarely, a cancer called an injection-site sarcoma develops where vaccines or other injections are given, such as between the shoulder blades, on the back or on the hind legs. The 2020 AAHA/AAFP Feline Vaccination Guidelines give a "3-2-1" rule for a lump at a vaccination site. A biopsy is warranted if the lump:
- is still there 3 months after vaccination,
- is larger than 2 centimeters (a little under an inch) across, or
- is still growing 1 month after vaccination.
Keep it in proportion: Merck puts the risk at about 1 in 10,000 vaccine doses and says the protection vaccines give outweighs it.
Mammary (breast) lumps
Cats have two rows of four mammary glands along the belly, each with a nipple. According to the Cornell Feline Health Center, a mammary tumor can start as a small, firm nodule about the size of a BB near a nipple, and about 85% of mammary cancers in cats are malignant adenocarcinomas, which tend to spread. More than 95% occur in females, and spaying young greatly lowers the risk. Any lump along your cat's belly line needs a prompt vet check.
Ticks
A tick can feel just like a small lump. One that has just attached looks flat; after a few days of feeding it swells into a rounded, bean-like bump. Ticks are less common on cats than on dogs, but outdoor cats often pick them up, and they can carry diseases. Ask your vet which tick prevention suits your cat (our guide to external parasite prevention for cats covers the options), and see your vet if a bite site turns red or swollen.
Lymph nodes and nipples
Some lumps are normal anatomy: lymph nodes (the easiest to feel are under the jaw and behind the knee) and the nipples along the belly. If your vet tells you the lump you found was one of these, don't be embarrassed. They would much rather check a normal nipple than miss something that needed treatment.
Why You Shouldn't Squeeze or Drain a Lump
It's tempting to give a lump a gentle squeeze to see what's inside. Please don't. The Merck Veterinary Manual is direct about keratin cysts in cats: squeezing releases keratin into the surrounding tissue and sets off severe inflammation, so a quiet little bump can turn into a much larger, sorer one. Breaking the skin also lets bacteria in. And you can't know it's a cyst in the first place. The same goes for lancing, draining or home remedies. If a lump bursts on its own, call your vet and ask what to do until they can see your cat.
How Your Vet Works Out What It Is
Your vet will ask when you first noticed the lump, whether it has changed, and how your cat is otherwise. They'll examine it, measure it so there's a baseline for later, and check the rest of the skin. Point out every lump you've found, not just the one that worried you. As Dr. Ettinger puts it, even an experienced cancer specialist can't look at or feel a mass and know what it is.
From there, the usual next steps are:
- Fine needle aspirate (FNA): your vet slides a thin needle into the lump to collect cells. It's quick and can usually be done during the appointment. The cells go on a slide for cytology, an examination under the microscope, often by a veterinary pathologist at a lab.
- Biopsy: if the needle sample isn't clear, or the lump needs to come out anyway, a piece of the lump (incisional biopsy) or the whole lump (excisional biopsy) goes to a lab for histopathology. A pathologist confirms what it is and, if it was removed, checks the edges (the "margins") to see whether all of it came out. For a suspected vaccination-site tumor, the guidelines recommend taking a piece first, because a needle sample may not give an answer.
A suspected cancer may also need blood tests or imaging.
Treatment Depends on What It Is
Once your vet knows what the lump is, the plan follows from it. For a lump a sample has shown to be benign, that isn't ulcerated or bothering your cat, no treatment can be the most sensible choice, especially in an older cat; your vet measures it and rechecks it at later visits.
Surgery is the usual treatment for cysts and many tumors. For a malignant tumor, your vet also removes a margin of healthy tissue and may refer you to a veterinary oncologist. Abscesses, eosinophilic lesions, acne and stud tail are managed by treating what's driving them, and your vet chooses any medicines and doses.
When to Call Your Vet About a Lump
Every new lump gets a vet check; the tiers are about how soon.
- Call now: a lump that is hot, painful, swelling quickly, bleeding, oozing or has burst; or any lump on a cat that is tired, feverish, hiding or not eating.
- See your vet soon: any new lump; a lump that has changed in size, shape or color; a lump near a nipple; a pea-sized (1 centimeter) lump that has been there for a month, which oncologist Dr. Ettinger says should be sampled, not just watched; a vaccination-site lump that meets the 3-2-1 rule; a sore on the ears or nose that won't heal.
- Mention at your next visit: a lump your vet has already sampled and diagnosed that hasn't changed at all.
Checking Your Cat for Lumps
You can't prevent most lumps, but you can find them early. The Cornell Feline Health Center suggests a monthly check for new lumps.
- Run your hands over your cat from nose to tail, including the chin, ears, armpits, belly and the base of the tail.
- Feel along both rows of nipples on the belly, where mammary lumps start small.
- For each lump, note where it is, its size compared with something familiar (a pea, a grape), and the date you found it. A quick photo helps.
- Book a check rather than waiting to see if it goes away.
If you also share your home with a dog, our guide to sebaceous cysts on dogs covers the canine side.
Originally written by Helen Roberts. Updated by the I Love Veterinary editorial team.
Sources
- Merck Veterinary Manual: Tumors of the Skin in Cats
- Merck Veterinary Manual: Epidermal and Hair Follicle Tumors in Animals
- Merck Veterinary Manual: Eosinophilic Granuloma Complex in Cats
- Merck Veterinary Manual: Ticks of Cats
- Cornell Feline Health Center: Eosinophilic Granuloma Complex
- Cornell Feline Health Center: Mammary Tumors
- Cornell Feline Health Center: Warning Signs of Cancer
- Cornell Feline Health Center: Feline Vaccines: Benefits and Risks
- AAHA/AAFP: 2020 Feline Vaccination Guidelines
- Today's Veterinary Practice: Tumor Detection in Dogs and Cats (Sue Ettinger, DVM, DACVIM)
- VCA Animal Hospitals: Abscesses in Cats
- VCA Animal Hospitals: Stud Tail (Tail Gland Hyperplasia) in Cats
- Texas A&M College of Veterinary Medicine: Managing Feline Acne
This article is for general information and is not a substitute for advice from your veterinarian.
