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Why Does My Cat Have A Fluid-Filled Lump?

Cuddling up and petting your cat is one of the most enjoyable parts of being a pet parent. Not only is it a special time to bond with your cat, but it can also be informative. For example, you might notice lumps and bumps on your cats that weren't there before. If your cat has a fluid-filled lump anywhere on their body, it could be an indication of a health problem. 

A fluid-filled lump typically feels like a bump on or under your cat's skin, but it's softer than your average lump, indicating it's filled with some type of fluid. Of course, your cat can get other types of lumps that are harder, too. Fluid-filled lumps can be small but grow over time. 

Any time you notice something new on or under your cat's skin, you should get it checked out by a vet. Whether your cat has a fluid-filled lump on their head, body, legs, tail, or anywhere else, you and your vet need to know what's causing it and how to treat it. Infections, inflammation, and tumors are all possible reasons why your cat has a fluid-filled lump. This article will discuss the causes of fluid-filled lumps on cats, diagnosis, and treatment. Let's get started. 

Fluid-Filled Lump Causes 

If your cat has a fluid-filled lump, it could indicate various health problems, with some being more severe than others. These are some of the potential causes of fluid-filled lumps in cats. 


1. Cyst

If your cat has a fluid-filled lump under their skin, it could be a cyst formed by a blocked hair follicle. Cysts are hollow bumps filled with fluid and may occur in multiples.1 Sebaceous cysts can ooze or rupture, so it's important to visit your vet as soon as possible to prevent serious infection. As a pet parent, you shouldn't treat cysts at home. Your cat can have a sebaceous cyst just about anywhere on their body, but they typically appear on the chest, sides, and legs.

Sebaceous cysts are fluid-filled bumps that are non-cancerous and likely don't cause any pain. They will look like an oval lump on your cat that's firm with a soft center. Since cysts can continue to grow until they rupture, it's important to visit your vet as soon as possible to remove the cyst and prevent possible problems later on.

When you take your cat to the vet, they'll have a physical exam that allows the vet to look at the cyst and determine whether there are any more. Cysts can look like tumors associated with skin cancer, so your vet might choose to biopsy your cat's skin to confirm that it's not cancerous.

Once your vet confirms that your cat's fluid-filled lump is a cyst, they can start treating it. If the cyst isn't growing, your vet might choose to leave it as long as it's not uncomfortable for your cat. On the other hand, if your cat has a big fluid-filled lump or cysts that are growing, they will likely require surgery that will remove the hair follicle and cyst wall. 


2. Abscess

    An abscess occurs when a large pocket of pus forms under the skin.1 These infections typically develop after a wound has healed and pus is being prevented from draining. Abscesses appear as fluid-filled lumps containing swollen tissue and are most typically found on a cat's arm or leg if they've been scratched or bitten or their skin has been punctured somehow. 

    Treatment for abscesses depends on where the infection is, but most are treated easily. First, your vet will likely remove the pocket of pus by surgical methods or draining and flushing. Your vet may also prescribe antibiotics to treat the abscess and any infections, based on the type of bacteria involved.


    3. Tumor

      If your cat has a fluid-filled lump, it may also indicate the growth of a tumor. Tumors can appear anywhere on your cat's body, and some are cancerous while others are non-cancerous.1 Cats with tumors are typically older, but cancer can affect cats of all ages. If your vet believes your cat's fluid-filled lump could be cancerous, they will perform a biopsy to identify the type of tumor it is to come up with a treatment plan. Different types of treatment for tumors in cats are:

      • Surgery
      • Chemotherapy
      • Radiotherapy

      Types of tumors

      Several different types of tumors can occur in cats, but these are the most common. 

      Basal Cell Tumors: Basal cell tumors are the most common type of skin tumor in cats, but they are benign. Basal cell tumors are typically small, firm lumps that can be found on the cat's head and neck and are removed via surgery.

      Squamous Cell Carcinomas: These tumors are typically found around the ears, nose, and eyelids of senior cats and are cancerous. During the early stages of squamous cell carcinoma, the skin may look like scabby, red skin or a skin rash, but it worsens over time. While this type of cancer rarely spreads throughout the body, it can be fatal. Early treatments are most successful, and your vet may recommend surgery or radiotherapy. 

      Mast Cell Tumors: Mast cell tumors can occur in singles or multiples, most commonly around the head and neck, but they can also occur near the spleen, liver, and bone marrow. These tumors are not usually aggressive, and surgery can remove them easily.

      Sebaceous Adenomas: Sebaceous Adenomas can look and feel like warts and occur anywhere on the cat's body. Sebaceous adenomas are typically benign but can be removed if they are causing your cat discomfort. 


      4. Fibromas

        Fibromas begin in the middle layer of skin, also known as the dermal layer, and have defined edges.Fibromas are common in domestic animals and are usually benign but appear as raised lumps that can be soft and fluid-filled. In most cases, treatment will be optional unless the fibroma is interfering with your cat's daily life.


        5. Lipomas

          Lipomas are benign fatty tumors typically found in senior cats commonly found on the abdomen.2 Lipomas may feel soft and fluid-filled and even move around when touched. While lipomas are benign, they should be surgically removed because they can grow.


          6. Acne

            Cat acne is another cause of fluid-filled lumps in cats and can occur for many reasons, including when the hair follicles produce too much oil.3 Cat acne can appear as small, raised bumps or larger fluid-filled lumps on your cat, most commonly on their faces and chins. Cat acne is simply a cosmetic problem unless it causes infection. In most cases, you'll be able to treat your cat's acne by keeping their faces clean. However, if your cat's acne doesn't clear up over time, you might seek veterinary care to help clear up your cat's acne, especially if it's affecting their quality of life. 

            Bee sting or insect bite

            7. Bee Sting Or Insect Bite

              Like humans, cats can be stung or bitten by insects, which can cause inflammation and swelling along with an allergic reaction.4 Signs of an allergic reaction include minor symptoms such as a lump with swelling and major symptoms such as diarrhea, vomiting, and weakness. If your cat is having any type of allergic reaction, seek veterinary care immediately since they can be life-threatening.

              When To See A Vet

              There are many reasons cats can develop fluid-filled lumps on their skin. Some causes of lumps are benign and non-life-threatening, while others, such as tumors, can be life-threatening. If you notice a lump on your cat's skin, call your vet for an appointment. You should also be prepared to answer questions about when you noticed the lump, how big it is if it's growing, and if it seems to be causing your cat any discomfort. 


              To effectively treat your cat for fluid-filled lumps, your vet must diagnose them. Since there are many causes for lumps on your cat, a vet may diagnose your cat in the following ways:

              • A skin scrape or impression smear: Skin scrapes involve taking a sample from the top layer of your cat's skin above the lump and looking at it through a microscope. 
              • A fine needle aspirate: Your vet will insert a small needle into your cat's lump to test the cells within. 
              • A biopsy: A biopsy requires your vet to take a small tissue sample and send it to a pathologist to help identify the cause of your cat's lump. 


              Based on the diagnosis, your vet will form a treatment plan that depends entirely on the cause of the lump on your cat. For example, if the lump is a tumor, they will determine the type of tumor and decide whether to use surgery or cancer treatment. On the other hand, a lump caused by an insect bite might be treated with anti-inflammatory medications and topicals. 

              Cat owner with cat in lap attending pet telehealth appointment via laptop

              Final Notes

              Whether it's skin tags, moles, growths, or tumors, feeling a lump on your cat can be scary, but you should always go to the vet as soon as possible to have them diagnose and treat it. There are many causes of fluid-filled lumps on cats, including cysts, abscesses, tumors, acne, and other various skin conditions. While it might be concerning to have to get a lump diagnosed by the vet, it's necessary for the health and wellness of your cat. Not only can going to the vet give you peace of mind, but it can also help you catch health conditions before they worsen, giving your cat their best chances of success. 

              Dutch offers telemedicine for pets to help your pet live a better life. Going to the vet can be stressful for pets and their owners, so instead of worrying about grabbing all your cat treats, harnesses, leashes, carriers, and more, you can have a vet visit from the comfort of your own home to help you handle a variety of medical conditions.


              1. Jennifer Coates, DVM. “Lumps, Bumps, Cysts, and Growths on Cats.” PetMD, PetMD, 5 Nov. 2020,

              2. Villalobos, Alice E. “Tumors of the Skin in Cats - Cat Owners.” Merck Veterinary Manual, Merck Veterinary Manual, 18 Apr. 2022,,underlying%20muscle%20and%20connective%20tissue.

              3. “Managing Feline Acne.” CVMBS News, 11 Mar. 2022,

              4. “Bee Sting Safety: Cats.” SF SPCA, 5 May 2021,

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