Lumps and Bumps. What’s That Hard Mass Under My Cat’s Skin?


Lumps and bumps are abnormal masses of tissue that form underneath a cat’s skin or fur. They come in all shapes, sizes and textures, and can occur anywhere on the cat’s body. While some lumps are benign and harmless, others can indicate more serious medical conditions like cancer. Lumps in cats can be concerning for pet owners, and often raise questions about what’s causing them and whether they require treatment.

This article provides an overview of the most common causes of lumps and bumps in cats. It discusses the typical symptoms of various types of masses, from benign cysts to malignant tumors. Diagnostic steps for identifying the lump are outlined, along with details on available treatment options. The article also offers guidance on when veterinary care is recommended, and provides tips for monitoring lumps at home and potentially preventing recurring growths.

By reviewing the comprehensive information in this guide, cat owners will gain a better understanding of the possible sources of skin masses. The goal is to address common owner concerns and questions about mysterious lumps and bumps in cats, so readers feel informed and empowered to make decisions regarding their pet’s health.

Possible Causes

There are several potential causes for lumps under a cat’s skin, including:


Cysts are fluid-filled sacs that form under the skin. They are benign but can grow and cause discomfort. Cysts often form on the head, neck, legs, or torso. They feel like soft, movable lumps under the skin. Cysts are common in cats and may resolve on their own or can be drained if troublesome.1


Abscesses are pockets of pus caused by bacterial infections. They may start from a bite wound, scratch, or foreign object that introduces bacteria under the skin. Abscesses feel like firm, painful masses that are hot to the touch. They require antibiotic treatment and draining to resolve.2


Feline skin tumors may be benign growths or cancerous. Common forms include mast cell tumors, squamous cell carcinoma, and basal cell tumors. Tumors can vary greatly in appearance and feel. Any new lump on senior cats or fast-growing mass should be checked by a vet.3


Sebaceous cysts are one of the most common causes of lumps under a cat’s skin. They are benign fluid-filled sacs that form when a hair follicle or oil gland gets damaged and blocked. The medical term for these cysts is an epidermal inclusion cyst.

Sebaceous cysts often feel round and firm. They form under the skin and can range from pea-sized to a few centimeters across. The cysts contain thick, yellowish fluid comprised of fatty acids and cellular debris. They are usually slow-growing and painless.

Sebaceous cysts develop when a hair follicle or sebaceous gland gets obstructed. This obstruction causes secretions to get trapped, forming a sac. Specific causes include:

  • Genetics
  • Skin trauma
  • Allergic reaction
  • Chronic skin inflammation

To diagnose sebaceous cysts, vets perform a physical exam and fine needle aspirate. This involves inserting a small needle into the cyst and withdrawing some fluid for examination under a microscope. Cytology can help rule out cancer.

Treatment options for sebaceous cysts include:

  • Surgical removal – This completely eliminates the cyst and prevents recurrence. It is the preferred treatment if the cyst is large, growing, or interfering with normal function.
  • Drainage – A vet lances the cyst with a scalpel and drains the contents. The empty sac may slowly shrink. This carries a risk of infection and recurrence.
  • Observation – Small sebaceous cysts that don’t bother the cat may simply be monitored. But they could enlarge over time.

According to, topical antibiotic ointment can help prevent infection after surgical removal or drainage. Pain medication may also be prescribed. Most cats recover fully with minimal scarring.


Abscesses are pockets of pus that form under a cat’s skin when bacteria infects a wound or area of infection. They typically appear suddenly as a painful swelling that may feel firm or fluid-filled. Abscesses often form after cat fights, bites, or scratches that introduce bacteria under the skin. They can also develop from infected anal glands, tooth infections spreading under the skin, grass seeds or foxtails getting trapped, and more (Abscesses in Cats – VCA Animal Hospitals).

Common symptoms of an abscess include:

  • Sudden swelling under the skin
  • Firm, fluid-filled lump
  • Pain and tenderness
  • Reddened skin over the abscess
  • Crusting or draining wound over abscess
  • Loss of appetite
  • Lethargy
  • Fever

To diagnose an abscess, a veterinarian will examine the cat and perform tests like a needle aspirate to check for pus. Treatment usually involves draining the abscess and flushing it, along with antibiotics. Severe or recurring abscesses may need surgical treatment. Abscesses should not be left untreated, as they can rupture internally and cause a life-threatening infection if the bacteria spreads. With prompt veterinary treatment, most abscesses can be resolved.

Prevention involves keeping cats up to date on vaccines, preventing fights between household cats, and checking for foxtails or grass seeds after time outdoors (Cat Abscesses – Causes & Treatment). Monitoring any wounds or swollen areas and seeking prompt treatment can also reduce the risk of abscesses developing.


Various types of tumors and cancer can cause lumps under a cat’s skin [1]. Tumors may be benign (non-cancerous) or malignant (cancerous).

Common benign tumors include lipomas (fatty tumors), sebaceous adenomas (oil gland tumors), and mast cell tumors. Lipomas are soft, moveable lumps under the skin, while sebaceous adenomas appear as firm nodules. Mast cell tumors can appear raised and hairless. Benign tumors tend to grow slowly and usually don’t spread to other areas of the body.

Malignant tumors include squamous cell carcinoma, basal cell carcinoma, mast cell sarcoma, and fibrosarcoma. Squamous cell carcinoma may start as thickened skin or scabs before becoming an open, oozing wound. Basal cell carcinoma often looks like a pearl-shaped bump or sore. Malignant tumors tend to grow quickly, often ulcerate, and can spread to other parts of the body [2].

Any new lumps or bumps on a cat should be checked by a vet, especially if they change shape or size. Biopsies are needed to determine if a mass is benign or malignant. Treating tumors and skin cancer in cats as soon as possible is important for the best prognosis.

Allergic Reactions

Allergic reactions can cause raised lumps and bumps on a cat’s skin. Cats can have allergic reactions to things like food, medication, vaccines, insect bites or stings, and environmental allergens. These allergies cause the cat’s immune system to overreact, triggering inflammation, itchiness, and hives or bumps on the skin.

Food allergies are a common cause of skin reactions in cats. The bumps may appear shortly after eating the food they are allergic to. Common food allergens for cats include beef, dairy, fish, chicken, or grains like corn and wheat. Medication allergies can also lead to hives, swelling, and bumps. Vaccine reactions may cause facial swelling and hives. Flea bite allergies are very common in cats and can result in small itchy bumps, especially around the head, neck, and base of the tail.

To diagnose a suspected allergy, the vet will take a history of symptoms and may recommend an elimination diet trial or allergy testing. Treatment involves removing the allergen and controlling the reaction with anti-itch medication, steroids, or immunotherapy. Once the allergy is identified, avoiding that allergen can prevent further reactions.


To determine the cause of a lump or bump under a cat’s skin, a vet will typically start with a physical exam, closely inspecting and palpating the area. They may look for key characteristics like size, texture, mobility, and whether it’s painful. Aspiration with a needle to extract cells for examination under a microscope can help rule out cysts or abscesses. A biopsy may be recommended to remove all or part of the lump for laboratory analysis if cancer is suspected. X-rays, ultrasounds, or other imaging tests can also be used to look inside the lump. Bloodwork may help uncover any abnormalities or inflammation. The vet will consider the cat’s medical history, age, lifestyle and if the lump has changed over time. Proper diagnosis is important so the most suitable treatment plan can be determined.


The treatment for lumps under a cat’s skin depends on the underlying cause. Here is an overview of common treatment approaches:

For benign cysts or abscesses, the vet may recommend draining the fluid or pus by aspirating it with a needle. They may also prescribe antibiotics and anti-inflammatory medications. Surgical removal is sometimes necessary if the lump continues growing back.

For malignant tumors, surgery is usually recommended to fully remove the cancerous tissue. This may be followed by chemotherapy or radiation treatments. Specific cancer treatments will depend on the type and stage of cancer.

For allergic reactions, treatment focuses on managing the allergy with medications like antihistamines, steroids, or immunotherapy. Eliminating exposure to the allergen is also important.

The most critical step is having any new, growing, or painful lump examined by a vet as soon as possible. Early evaluation and diagnosis is key to effective treatment. A vet can make the proper diagnosis and recommend the appropriate treatment plan based on the specific cause of your cat’s skin lump.


There are several steps cat owners can take to help prevent lumps from developing:

  • Keep up with vaccines – Vaccines like the feline leukemia vaccine can help prevent viral infections that may cause lump development.
  • Use flea and tick prevention – Parasites like fleas and ticks can cause allergic reactions and abscesses. Using monthly flea/tick medication can help repel these pests.
  • Avoid trauma – Preventing injuries that could lead to hematomas or seromas developing into fluid-filled lumps.
  • Spay/neuter your cat – This can reduce the risk for mammary tumors and some types of reproductive cancers.
  • Don’t allow outdoor roaming – This reduces the risk of abscesses from bites and scratches.
  • Brush regularly – Helps prevent matted fur which can hide lump development.
  • Provide a healthy diet – A nutritious diet supports your cat’s immune system.
  • Limit sun exposure – Can help prevent solar comedones and sun-related skin cancers.

While not all lumps can be prevented, staying on top of your cat’s health and minimizing exposure to parasites, viruses, trauma, and sun can reduce the chances of lump formation.

When to See the Vet

While some lumps and bumps on a cat may be harmless, there are certain warning signs that require urgent veterinary attention. These include:

  • Rapid growth of a lump over days or weeks
  • Ulceration, bleeding or discharge from the lump
  • Lump is fixed to underlying tissues rather than freely moveable
  • Lump is over 2 cm in diameter
  • Lump is rapidly growing and interfering with movement
  • Your cat seems lethargic, loses appetite, or shows other signs of illness
  • Lump is hot, painful, or swollen

According to veterinarians, any lump that seems suspicious or is causing discomfort should be evaluated by a vet as soon as possible. Early detection and treatment greatly improves outcomes for conditions like abscesses or cancer. Even if the lump turns out to be benign, your vet may recommend removal or continued monitoring. Don’t wait to see if it goes away on its own – call your vet promptly when you notice any abnormal lumps or skin changes in your cat.

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