Cat Skin Lumps, Bumps, and Cysts

By Katie Grzyb, DVM on Jul. 25, 2022

older woman sitting on bed and petting white cat

Not sure whether to see a vet?

Answer a few questions about your pet's symptom, and our vet-created Symptom Checker will give you the most likely causes and next steps.

What Causes Tumors on Cats?

A tumor is an abnormal growth of cells. Tumors that affect the skin or the subcutaneous tissue, the tissue directly below the skin, are the most common in cats. Veterinarians believe this is because the skin is always exposed to tumor-causing environmental factors such as UV radiation, viruses, and chemical pollutants, similar to humans. Tumors can also be caused by genetic or hormonal issues.

What to Do If You Find a Lump or Bump on Your Cat

If you find a mass on your cat during a grooming or while petting them, schedule an appointment with your veterinarian. They will perform diagnostic testing to investigate the cause, and whether the mass could become a larger issue or needs treatment now.

Lumps That Show Up on Your Cat Overnight

It is common for a mass to develop so fast that it seems like it popped up overnight on your cat. These are often raised, reddened masses that can be benign or malignant. It is important to schedule an appointment with your veterinarian if you find a lump or bump on your cat, especially if it:

Does not go away within a week
Grows larger quickly
Changes color
Seems to bother your cat

Types of Lumps and Bumps on Cats

Masses on cats can be either benign or malignant. Benign masses are defined as tumors that do not spread, or metastasize, to other areas of the body. Usually, benign masses do not have invasive characteristics, while malignant (or cancerous) tumors can attack the surrounding tissue or spread.

Speedy diagnosis and treatment of malignant tumors is necessary to give your cat the longest and best quality of life possible. If you are concerned about abnormal skin lumps on your cat, contact your veterinarian so they can give a thorough physical examination and do diagnostic testing.

Benign Lumps and Bumps on Cats

Some masses are benign and require little to no therapy. Here are some common reasons for benign tumors in cats:

Trauma: If a cat bumps a part of their body, lumps or firm bruises can form in these areas. These types of bumps usually go away in less than a week.

Insect/Parasite Bites: These often show up as red, raised areas and frequently cause irritation or itching. You may see fleas in the area, or a tick feeding on the skin. Spider bites and ant bites look similar to flea and tick bites. These red bumps usually go away within a few days, but they can cause concern for pet parents.

Allergic Reaction/Anaphylaxis: Some environmental irritants, such as foods or insect bites, can cause hives, which cause itchy bumps that can be flattened or raised and sometimes reddened. This is often a benign process, though some malignant tumors (specifically, mast cell tumors) can cause the body to react this way.

Skin Tags: These skin growths are benign overgrowths of skin cells that can pop up anywhere on the body. Usually, these are small and do not bother the cat at all. They do not grow quickly and usually do not change color unless they are irritated.

Abscesses: An abscess is a walled-off infection within tissue. The infection develops underneath a healed wound, and this prevents the infected fluid (or pus) from draining.

Abscesses are often associated with puncture wounds, such as animal bites or scratches, and they can be found anywhere on a cat’s body. They are most commonly seen in outdoor cats due to fighting. An abscess usually starts forming with little to no clinical signs, and the puncture wounds are usually small and hidden in the fur.

Eventually, they start to swell and become warm and painful. Left untreated, abscesses can cause fevers, pain, and lethargy in cats. Sometimes these lumps can come to a head, burst, and drain pus and sometimes blood.

Abscesses should be treated by a veterinarian. They will probably surgically drain the abscess, thoroughly clean the area, and prescribe antibiotics and pain and anti-inflammatory medications.

Cysts: These benign masses often contain fluid or thicker, non-infected material. They are usually raised and can be round or oval, firm or soft. The inner lining of the cyst wall contains cells that secrete material or fluid until the entire lining is removed.

Cysts are usually not painful, but they can get inflamed or infected over time, especially if your cat is bothering the area consistently. Draining the cyst can be helpful, but surgical removal is usually necessary, so the cyst doesn’t keep refilling.

Certain types of cysts are seen frequently in animals.

Sebaceous adenomas (or sebaceous cysts) often look like warts and appear most commonly on the head, though they can be found anywhere on the body. They form within the skin’s hair follicles when oil clogs the area or the follicle becomes inflamed. Surgical removal will usually cure these types of cysts.

Another common condition in cats is apocrine gland cystadenomatosis, which presents as dark-colored cysts inside the ear. You will usually find several of them together in the ear. Although the cysts are benign, they can cause pain if they become infected, drain into the ear canal, or grow large enough to block the ear canal. Your veterinarian may recommend surgical removal of the cysts.

Granulomas: These areas of chronic inflammation form a solid mass that is often gritty in consistency. Granulomas can appear as small, raised, well-delineated masses or as red, raised, ulcerated areas of skin that can have a “ground glass” appearance.

Cats can develop a condition called eosinophilic granuloma complex (EGC) that makes them prone to granulomas. This condition is often associated with allergies and/or genetic predisposition. It’s often treated with steroid therapy or other immunosuppressive medications. There are three forms of eosinophilic granuloma complex:

Eosinophilic granulomas (also called linear granulomas) are raised, hairless, bumpy, reddened, linear skin lesions around the thighs, lips, feet, or chin.
Eosinophilic plaques are raised, reddened, bumpy, often ulcerated and painful regions of skin most commonly seen on the abdomen, groin, or inner thigh, or around the anus.
Indolent ulcers (also called rodent ulcers) are reddened, thickened, ulcerated areas around the lips and sometimes the tongue and gums.

Lipomas: These are benign fatty tissue growths that are usually felt under the skin around the abdomen, flank, or neck of a cat. They do not tend to grow from the skin itself, but underneath the skin, in the subcutaneous tissue. These tend to be slow-growing, non-painful tumors. Surgical removal may be recommended by your veterinarian.

Warts: These are benign, bumpy growths found on cats’ skin. Warts (also called papillomas) are caused by papillomavirus and are rarely seen in cats. Papillomas often form when a cat’s immune system is suppressed, which is why they’re more common in younger and older cats. These tend to resolve on their own within 1-3 months, but surgical removal will also cure warts.

Horned Paw: These benign growths, also called cutaneous horns, are often thin and horn-like and show up in a cat’s paw pads. They are caused by keratin overgrowth within the skin, similar to callus formation in humans.

These growths are usually harmless and cause no pain unless they are found on weight-bearing regions of the paw, which can lead to irritation and infection from rubbing. Your vet can trim or surgically remove these growths if they become a nuisance to your cat.

Acne: Cats are prone to feline acne or pimples that tend to develop around the lips, chin, and/or face. Similar to humans, cat acne is caused by oils clogging the pores. It is believed that feline acne is due to allergies and/or genetics.

Using ceramic or stainless-steel food and water bowls is recommended, as cats can be prone to plastic allergies that can set off acne. Certain cat shampoos, topical ointments, or medicated wipes may be recommended to help treat the affected areas.

Malignant Lumps and Bumps on Cats

A University of Missouri study documented benign and malignant cat skin tumors in 340 cats. Just four malignant tumor types made up 77% of all the cases reviewed:

26% basal cell tumors
21% mast cell tumors
15% squamous cell tumors
15% fibrosarcomas

The four are the most common skin tumors in cats, both benign and malignant.

Some of these tumors can spread rapidly, affect other organs, and be fatal. This is why it’s important to identify, diagnose, and treat cat skin masses as soon as possible.

Here is a brief description of the most common types of malignant tumors in cats:

Basal Cell Tumors: These are the most common type of skin tumor in cats and are usually found in middle-aged and older cats. Only 10% of basal cell tumors tend to spread. Basal cell tumors are small, firm masses most commonly seen around a cat’s head and neck. Breed predispositions include Sphynx, Siamese, Persian, and Himalayan. These tumors can usually be cured through surgical removal.

Squamous Cell Carcinomas: These malignant tumors are usually seen in middle-aged and older cats. They’re found in areas with little hair or skin pigmentation, usually around the head, ears, nose, and mouth. Squamous cell carcinomas do not often spread through the body, but they tend to quickly grow into the skin surrounding the original tumor.

This tumor needs speedy diagnosis and therapy, as it can lead to infection, pain, and death if left untreated. Treatment often includes surgery to remove the tumor, as well as radiation and/or chemotherapy.

Mast Cell Tumors: These skin tumors are most commonly found around the head and neck, but they can invade any part of the body. Mast cell tumors affect cats of any age, but more often middle-aged and older cats. They can spread to organs such as the liver or spleen, or even the bone marrow.

If the tumor is only affecting the skin, surgically removal will often cure it, but if it has spread to other organs, the prognosis is more guarded. In this case, surgery, radiation, chemotherapy, and sometimes removal of the spleen is recommended to attempt remission.

Fibrosarcomas: These tumors often affect the limbs or between the shoulder blades in middle-aged and senior cats. These are very aggressive tumors, and though they do not often spread to distant organs, they are quite locally invasive.

They usually start small and firm, then grow quickly into the surrounding area. Injection-site fibrosarcomas are common, which is why vaccines should be given lower on a limb or in the tail, if possible.

This makes surgical removal easier if a fibrosarcoma forms, since amputation is often the recommended surgery, due to the cancer’s aggressive nature. Surgery is commonly followed up with radiation and/or chemotherapy.

How Vets Diagnose Lumps, Bumps, and Cysts on Cats

Your veterinarian will likely assess the mass in terms of color, size, consistency, and movement (growing into the underlying tissue or only felt on the skin).

Often, a fine needle aspirate and cytology will be performed. This is where a small needle is used to obtain a sample of cells from the mass, which are sent to a laboratory for assessment by a pathologist.

With some masses, it’s easy to diagnose them using this test alone. With other masses, like fibrosarcomas, fine needle aspiration might not give you an answer because the cells of the tumor hold on tightly. These masses require surgical biopsy to remove either the entire mass, if possible, or a piece of the mass for testing.

Treatment for Lumps and Bumps on Cats

Treatment ranges from local topical therapy and oral medications (such as steroids and immunosuppressive medications) to surgical removal of the mass. Depending on the type of mass, further therapy with radiation and/or chemotherapy may be necessary, especially if the tumor is locally invasive or has spread to distant organs.

How to Monitor Your Cat's Lumps or Bumps

Your veterinarian might ask you to monitor your cat’s mass. This means watching for any change in shape, growth, or color, and looking for any bleeding, discharge, pain, or itching.

Several times a week, measure the mass and take a picture of it to compare for changes. If you see any of the signs above, contact your veterinarian. They will likely recommend further diagnostic testing to keep your cat happy and healthy for as long as possible.

Featured image: iStock.com/PeopleImages