Types of Cysts, Lumps, and Growths on Dogs

Updated October 17, 2022
Veterinarian preparing the dog for surgery

Finding a lump, bump, or swelling on your dog can be a scary discovery. Regardless of your pet's age, a new growth could be a quickly developing malignancy, or it could be completely benign. There are different ways to diagnose and treat each type. An understanding of some basic characteristics of each can help you take the appropriate steps to figure out exactly what to do when you find a growth on your dog.

Why Do Dogs Develop Cysts, Lumps, and Growths?

Dogs develop masses for several reasons. They could be caused by an overgrowth of cells, a clogged hair follicle, or even an infectious virus. It's important to be able to differentiate between these three types of canine bumps.

  • Cysts. Cysts are encapsulated sacs of fluid or hardened material that create a lump. In general, the contents of the cyst can be squeezed out, but they tend to fill back up. Cysts are almost always nonmalignant.
  • Benign lumps. Noncancerous lumps can involve the skin cells or might sit just beneath the skin. These bumps don't necessarily have to be removed unless they interfere with your dog's ability to move or eat.
  • Tumors. Rapidly growing, abnormal cells can develop right under or on a dog's skin. Although not all growths are cancerous, many types of bumps are and can spread to other organs.

Common Types of Cysts on Dogs

The various types of cysts differ based on what type of gland or tissue they originate from. Generally, these bumps are more annoying than harmful to your dog. Some breeds may be predisposed to developing cysts, such as Schnauzers, Boxers, and Basset Hounds, among others.

Sebaceous Cysts

Plugged oil glands cause these common cysts in your dog's skin. They can resemble a pimple and may feel like a hard, raised bump. A sebaceous cyst may go away on its own after being expressed. However, if it comes back or becomes irritated, it may need to be removed by your veterinarian.

A Sebaceous Cyst on a dog

Follicular Cysts

These cysts form as a result of blocked or abnormal hair follicles and can contain fluid or cheese-like material. Follicular cysts usually begin as a small bump under the skin or can look like a whitehead. You should not squeeze them as they can easily become infected.

Follicular cyst on a dog's paw

False Cysts

A false cyst is a fluid-filled pocket under the skin that most commonly forms from trauma. It can resemble a hematoma, a blood-filled structure under your dog's skin. False cysts usually resolve on their own.

Common Types of Canine Lumps

There are a few types of benign lumps that dogs frequently develop. Unfortunately, it's impossible to determine if a bump is benign or cancerous just be looking at it.


Lipomas, or fatty tumors, are a very common type of lump in dogs. They are composed of a build-up of fatty tissue under the skin. Lipomas feel soft and movable and are usually painless. However, they can become very large and may restrict your dog's movement or feel uncomfortable depending on where they are located. In rare cases, lipomas may actually be a cancerous tumor called a liposarcoma. These bumps are usually found as a normal aging occurrence in older dogs, but obese dogs are more prone to them.

Veterinarian shows Lipoma on the dog's body


Histiocytomas are raised bumps caused by an overgrowth of immune cells. They are most often found in young dogs between 8 weeks and 6 years of age. Histiocytomas have a recognizable red, button-like appearance on the skin. These tumors are benign and often go away on their own. However, your veterinarian may recommend surgical removal, especially if your dog irritates the growth by licking, biting, or scratching at it.

Histiocytoma on dog

Skin Tags

Skin tags are common, especially among aging dogs. They tend to be the same color as the surrounding skin and dangle from your dog's body, as opposed to residing below or above the skin. The cause is unknown. Skin tags are non-cancerous and only cause problems if they become irritated or grow to significant sizes. These are often confused with canine warts.


Warts are technically called papillomas, as the papillomavirus causes them. This virus is contagious among dogs, but cannot spread to people or other animal species. Papilloma warts appear as small, cauliflower-like raised bumps that pop up quickly. They may be solitary or grow in clusters.

Warts can occur anywhere on a dog's body, but are most commonly seen around the muzzle, eyelids, paws, and genital areas. They tend to be harmless and only need treatment if they begin to bleed or interfere with your dog's ability to eat. If you believe your dog has warts, keep them away from other dogs to avoid the spread of the virus.

Cocker Spaniel Dog Breed with papilloma virus infection

Common Types of Cancerous Growths

If you've noticed a new growth on your pet's skin, your mind may immediately jump to "cancer." Unfortunately, some lumps are composed of rapidly growing cancer cells and can spread to other parts of a dog's body if not addressed quickly.

Soft Tissue Sarcomas

Soft tissue sarcomas originate from abnormal muscle, connective, or nervous tissue growth and can occur anywhere on your dog's body. These cancerous tumors may initially look like lipomas, but they increase rapidly in size, unlike lipomas. Depending on the growth's location, it can quickly become painful and inhibit your dog's movement.

For example, it may cause limping if the tumor is located on the leg. The larger the mass becomes, the more challenging it can be to remove surgically and the greater the chance of metastasis, or the development of secondary malignant growths.

Big tumor on the leg of a dog

Cutaneous Hemangiosarcoma

You may have heard of hemangiosarcoma tumors most commonly growing on a dog's spleen, but this type of tumor can also attack the skin. Cutaneous hemangiosarcomas are a dangerous skin cancer that dogs can develop as a result of sun exposure. They resemble a little red or black button on the skin, usually on the belly, and they often bleed.


Dogs can develop both benign melanomas and malignant melanomas, although the noncancerous variety is more common. These lesions appear on the skin as a small, pigmented growth. They can develop anywhere on the body, but malignant melanomas most often arise in dogs' nail beds, face, and oral cavity. Treatment involves surgical removal. In toenail tumors, amputation of the digit may be indicated. A vaccine is also available to prevent the spreading or metastasis of malignant melanomas.

Tumor on front dog's leg

Mast Cell Tumors

Mast cell tumors (MCT) are the most common cutaneous cancer in dogs and account for approximately 1/5 of all diagnosed masses. These bumps are a cancerous type of growth that often resembles the benign varieties of lumps. Unfortunately, this is one element that makes them particularly dangerous. Mast cell tumors can look like a small lump under the skin or a red, raised, ulcerated, or hairless bump above the skin. They may also spontaneously shrink or grow in size.

Other Types of Swellings

Some other types of firm swellings could be easily mistaken as growths.

Lymph Nodes

If the bumps you feel are symmetrical on either side of your dog's neck under their jaw line, they could be swollen lymph nodes. Palpably enlarged lymph nodes in a dog can indicate a serious systemic problem. This could point to an infection, virus, or cancer, so it's important to have them examined by your vet.

Professional veterinarian palpates some lymph nodes in dog


An abscess is an accumulation of infected fluid. These can occur anywhere in the body, but most commonly develop in an area of trauma such as a laceration or wound. Although the fluid-filled portion of the abscess is generally soft, the infected tissues can feel firm, just like a lump or growth. Thorough cleaning of the affected area (potentially under sedation if the tissues are particularly painful) and antibiotic therapy can resolve the infection.

Abscess on dog


A seroma is a pocket of fluid under a dog's skin. This most commonly occurs at a surgical site following a procedure if the patient is too active. Movement at the incision can cause inflammation and then an accumulation of fluid. The body often absorbs the fluid as the inflammation goes down, but sometimes your veterinarian may want to drain the fluid to make your pet more comfortable. To avoid a seroma, keep your dog quiet and calm while they are recovering from a procedure.

How to Tell if a Growth Is Cancerous

It is impossible to know just by looking at a growth whether it's cancerous or harmless. However, there are a few different diagnostic methods veterinarians use to determine whether a growth is concerning. In general, they will begin with the least invasive to get an idea of what type of cells the abnormal swelling or growth contains.

If a test is inconclusive, they may recommend a more aggressive method to get a definitive diagnosis. Your vet clinic may send the samples out to a reference laboratory for evaluation by a veterinary pathologist.

Painful hot spot on dog's front paw

Impression Smear

If the mass is ulcerated, meaning the surface of the skin on the growth is broken and bleeding or oozing, your vet might recommend an impression smear. This non-invasive diagnostic method involves taking a glass slide and pressing it directly against the mass. It's important to note that any cleaning solutions or ointments could interfere with this test, so avoid putting anything on an ulcerated mass before you head to your appointment.

Fine Needle Aspirate

Another simple and painless procedure is a fine needle aspirate. This involves inserting a slender needle into the lump. Pets generally tolerate this method very well. Because the needle is hollow, it will collect cells from within the mass, which the veterinarian will gently apply to a glass slide.

Tissue Biopsy

A tissue biopsy is slightly more invasive, as it involves removing a small piece of the growth. This is generally done under local or general anesthesia. Your veterinarian will surgically remove a portion of the mass and send it out to the laboratory to determine whether it is concerning or benign.

A veterinarian taking a biopsy of a tumor


Your vet may recommend removing the entire lump and sending it to the lab for analysis. This may be the case if it's affecting your dog's movement or daily life. Additionally, if your dog has developed cancerous growths in the past, removing a new mass immediately can prevent it from growing further. If the entire lump is evaluated and found to be cancer, the pathologist can advise your vet on whether they removed the lump with clear margins, meaning the edges are free of concerning tissues, ensuring no cancer was left behind.

When to Seek Veterinary Care For a Lump

Any abnormal swelling, lump, or bump that does not go away should be looked at by your veterinarian. Dr. Sue Ettinger, an accomplished veterinary oncologist, recommends early detection with her signature catchphrase, "Why wait? Aspirate!" She advises that, "When a skin mass is the size of a pea or larger or has been present for one month," it should be aspirated or biopsied. Early identification and treatment of malignant growths can save your pet's life.

Regardless of the size of a mass, if it rapidly grows in size or changes its characteristics quickly, have your veterinarian look at it immediately. Any mass that is painful, bleeding, or affects your dog's ability to move or eat should also be addressed right away.

Early Detection Is the Key to Prevention

It is very difficult to prevent most lumps and bumps. Lipomas can be prevented, in part, by keeping your dog at a healthy weight. Most other growths are out of a pet owner's control. The best you can do is to routinely feel your dog's body to identify any new masses. Make a note of any swelling or lump that you notice and bring it up to your veterinarian. Early intervention is key to treating any lumps that might be cancerous.

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Types of Cysts, Lumps, and Growths on Dogs