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Lumps, Growths, and Cysts on Dogs

Lisa K. Campbell, DVM
An old dog

Finding a lump, bump or swelling either above or under your dog's skin can be a scary discovery. Most lumps and bumps are found in older dogs but some are also common in puppies. There are different ways to diagnose and treat each one. An understanding of some basic characteristics of these can help you take the appropriate steps to figure out exactly what to do when you find one on your dog.

How to Identify a Lump, Bump or Cyst

Any swelling that is hard or soft in a place where it wasn't there before, is considered abnormal. There may or may not be pain associated with the swelling. A lump is a swelling under the skin and a bump is raised above the skin. Your veterinarian may refer to the lump or bump as a growth, or a mass. The skin may or may not appear red or irritated around the swelling.

A cyst is an empty space within tissues, and may contain liquid material or solid material. Cysts may feel soft and squishy, or spongy. The skin around a cyst can range from normal looking to slightly white or bluish in color.

Common Types of Lumps and Bumps

There are many types of lumps and bumps that a dog can develop. Some are benign (non-cancerous), and some are malignant (cancerous). Below is a list of some of the most common masses that occur in dogs.


A lipoma is a very common type of lump. It is made up of an abnormal build up of fatty tissue under the skin. Lipomas feel soft and movable and are usually painless and benign. However, they can grow to be very large and cause pain, depending on where they are located. In rare cases they may actually be a cancerous tumor called a liposarcoma. They are usually found as a normal part of aging in older dogs, but obese dogs are more prone to them.


This is a lump most often found in young dogs between the ages of eight weeks and three years of age. It has a red, raised button-like appearance above the skin. These tumors are benign and often go away spontaneously on their own. Histioctyomas can be problematic if your dog is licking, biting, or scratching at them, and causing irritation. They are caused by an over growth of a specific type of immune system cell.

canine cutaneous histiocytoma

Mast Cell Tumors

This is a cancerous type of lump that often looks like many of the other non- cancerous lumps, which is what makes them so dangerous. This tumor can look like a small lump under the skin, or a red, raised, ulcerated, or hairless bump above the skin. They may change in size and spontaneously become smaller or larger. Mast cells are a type of immune cell found in your dog's skin and other organs. They have an important role in managing inflammation and allergies.

Mast cell tumor on dog

Skin Tags

Skin tags are common and seen in aging dogs. The cause is unknown. They can be confused with warts. A skin tag is commonly teardrop shaped instead of round. They are usually very small, but can get larger. They tend to be the same color as the surrounding skin, and dangle from your dog's body, as opposed to being below or above the skin. Skin tags are non cancerous and only cause problems if they get irritated or grow to be very large.


Warts can be confused with skin tags. They are technically called papillomas because they are caused by a papilloma virus. This virus is contagious between dogs, but not to people or other types of animals. They start out as small cauliflower-like raised bumps that appear to pop up overnight. They may be solitary or grow in clusters. They can appear anywhere but are more commonly seen around the muzzle, eyelids, feet and genital areas. They tend to be harmless and only need treatment if they start to bleed, or your dog is chewing on them and causing trauma.

Soft Tissue Sarcomas

These are cancerous tumors that can initially look like lipomas. They come from an abnormal production of connective, muscle, or nervous tissue, and can show up anywhere on your dog's body. They feel like a firm or semi-firm lump in the deeper layers of skin, often under muscle tissue. They grow rapidly and press on the surrounding tissues. They can initially be non-painful, but as they grow pain can be related to the location of the tumor. Such as limping if the tumor is located on the leg.

sarcoma on the leg of a dog

Types of Cysts

Cysts are different from lumps or bumps and there are several types. Cysts are almost always non-cancerous.

Follicular Cysts

These form due to blocked or abnormal hair follicles and can contain fluid or cheese-like material. They usually start out as a small bump under the skin or can look like a whitehead. You should not squeeze them because they can become infected.

Sebaceous Cysts

These common cysts are caused by plugged oil glands in your dog's skin. They can resemble a pimple and will feel like a hard, raised bump. It may go away on its own or it could rupture and not need any treatment. If it comes back or gets irritated, it may need to be removed by your veterinarian.

False Cysts

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

How to Tell if a Mass Is Cancerous

The only true way to tell if an abnormal swelling or growth on your dog is cancerous is to have it surgically removed by your veterinarian. The entire mass will be sent to a veterinary lab where a pathologist will look at it under the microscope and determine if it is cancerous or benign.

There are other, less invasive and less expensive ways to gather information about the mass and determine if it is cancerous and needs to be removed.

Impression Smears

Ulcerated masses can be looked at by your veterinarian taking a glass slide and pressing it directly on the mass. The cells can then be looked at under the microscope to determine the type of growth it is, and if it is cancerous.

Fine Needle Aspirate

This is a fairly simple and painless procedure. A small needle attached to a syringe is inserted into the mass and cells are suctioned into the syringe and then smeared onto a glass slide. Your veterinarian may look at the slide in her clinic as well as send the slide out to a veterinary pathologist to identify whether there are cancer cells present.

Tissue Biopsy

A biopsy is taking a larger chunk of tissue than with a fine needle aspirate. This is done under local or general anesthetic. A large portion of the mass is removed surgically and sent to the lab to see if it is cancerous or benign.

When to Seek Care

Any abnormal swelling, lump, or bump that does not go away should be looked at by your veterinarian. If the mass just appeared, and it is small, it may be appropriate for you to monitor it for a few weeks before seeking care. Some lumps can even be caused by a bug bite or an injection. These types of swellings will go away within a few weeks.

If the mass appeared suddenly, but then gets bigger or changes quickly, it should be looked at immediately by your veterinarian. Any mass that is painful or ulcerated should be also be looked at right away.


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 lumps and bumps are out of a pet owner's control. The best you can do is to go over your dog's body once a month. 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.

Lumps, Growths, and Cysts on Dogs