Lumps and Bumps on Dogs: When to Worry

Common lumps on dogs

These are the lumps owners find most often. Only a test can confirm which one your dog has.

• Lipomas are soft fatty lumps under the skin and one of the most common benign tumors in dogs. They are seen most in older, overweight dogs, often on the chest, sides, and upper legs, and most move freely under the skin.
• Histiocytomas are small, raised, often hairless pink or red bumps, usually in dogs younger than three and a half years. They favor the head, ears, and legs, and most go away on their own within two to three months.
• Skin cysts form from hair follicles. They can hold a gray, brown, or yellow cheesy material and may burst.
• Warts (papillomas) are caused by a virus. Young dogs can get several at once, often on the lips and inside the mouth.
• Sebaceous adenomas are growths from the oil glands, often several at once and common on the head of older dogs. They are benign but can become irritated or infected.
• Hygromas are soft, painless, fluid-filled swellings over the elbows of large dogs that lie on hard floors.
• Mast cell tumors are the most common malignant skin tumor in dogs. Boxers, pugs, Boston terriers, and golden retrievers are among the breeds at higher risk.
• Mammary tumors are lumps along the teats of female dogs. About half of all tumors in female dogs are mammary tumors, and a little under half of these are cancer.

Looks and touch are not enough

A soft lump that moves under the skin is often just fat. This is only a rough guide. A mast cell tumor can look and feel exactly like a lipoma. Mast cell tumors can also swell and shrink from one day to the next, so they may seem to come and go. Some soft tissue sarcomas form a thin false capsule that makes them feel neat and well defined, while they actually reach into the tissue around them. Even veterinary cancer specialists say they cannot tell what a lump is just by looking at it or feeling it.

Some features raise more concern. These include fast growth, a firm lump that feels fixed to the tissue below, and a surface that is ulcerated or bleeding. Location matters too. Malignant melanomas tend to appear on the lips, in the mouth, and in the nail beds. A tumor in a nail bed can look like a swollen toe or a nail infection that does not clear up. Squamous cell carcinoma is linked to sun exposure and often appears on the lower belly of white-skinned, short-haired dogs such as Dalmatians, bull terriers, pit bull types, and beagles.

When to see the vet

Many veterinary cancer specialists use a simple rule. If a lump is the size of a pea or larger and has been there for a month, they recommend testing it with a needle or a biopsy. It is a good idea to book a visit sooner if you notice any of the following.

• A new lump in a middle-aged or older dog
• A lump that grows, changes shape or color, or feels different
• A firm lump that does not move under the skin
• Any lump in the mouth, on a toe, or around a nail
• Any lump along the teats of a female dog
• A sore or bleeding spot that does not heal
• A lump your dog keeps licking, scratching, or chewing

Before the visit, write down where the lump is and when you found it. Measuring it or taking a photo next to a coin helps you and your vet see whether it changes over time.

When it is an emergency

Most lumps can wait for a regular appointment. Some situations need same-day care. Contact your vet or an emergency clinic if a lump bleeds heavily or suddenly becomes swollen and red, or if your dog vomits, stops eating, seems weak, or passes black, tarry, or bloody stools. Mast cell tumors can release histamine and other substances when they are disturbed, and this can lead to stomach ulcers and bleeding. A lump that appears quickly and feels hot and painful may be an infection, which also needs prompt attention.

How vets check a lump

The usual first step is a fine needle aspirate. The vet slides a thin needle into the lump, collects a few cells, and looks at them under a microscope or sends them to a lab. It is a simple procedure done during a normal visit, and it often gives an answer. Veterinary references recommend this test before surgery. It can spare many dogs an operation for a harmless lump, and it helps the vet plan the right surgery for one that is not.

Sometimes the needle does not collect enough cells, or the result is unclear. The vet may then suggest a biopsy, where a small piece of tissue is taken, usually with sedation or anesthesia. A biopsy also allows a tumor to be graded, which shows how aggressive it is likely to be.

If a lump is cancer, the vet may check whether it has spread. This can include a needle sample from the nearest lymph node, chest X-rays, and an ultrasound of the belly. Any lump that is removed should go to a lab for a full report, even if it looked harmless.

How lumps are treated

Treatment depends on what the lump is. Many benign lumps can simply be watched. A histiocytoma often disappears by itself, and a small lipoma that is not growing or bothering the dog may be left alone. Your vet may still suggest removing a benign lump that grows large, gets infected, or gets in the way of movement.

Surgery is the main treatment for most skin tumors. For cancers such as mast cell tumors and soft tissue sarcomas, the surgeon removes the lump together with a wide border of healthy tissue. The first surgery gives the best chance of removing it completely, which is one reason a diagnosis before the operation matters. Some dogs also need radiation therapy or chemotherapy, especially when a tumor has a high grade or could not be fully removed. Your vet or a veterinary cancer specialist can explain which choices fit your dog and what outcome to expect.

After surgery, the lab report shows what the lump was and whether it was fully removed, and your vet can explain any follow-up checks.

Home checks and prevention

Most lumps cannot be prevented, but you can catch them early. Check your dog's skin regularly, for example while brushing, and include the lips, mouth, paws, nail beds, armpits, and belly. A few steps also lower specific risks. Spaying lowers the risk of mammary tumors, and the benefit is greatest when it is done before the first heat. Your vet can advise on the best timing for your dog. Light-skinned, short-haired dogs may benefit from shade and less time in strong midday sun, which can help protect against squamous cell carcinoma. Soft bedding protects the elbows of large dogs from hygromas. Keeping your dog at a healthy weight is good for many reasons, and lipomas are more common in overweight dogs.

It is best not to squeeze a lump that looks like a cyst, because the contents can leak into the surrounding tissue and cause inflammation. It is also wise not to poke or rub a known mast cell tumor, since handling can make it release its chemicals.

Lumps that can spread

Most lumps cannot pass to other pets or to people. Warts are the main exception among common lumps. The virus spreads between dogs through direct contact and shared items such as toys, bowls, and bedding, and it can affect several dogs where young dogs live together. Dog wart viruses are species specific, so they are not considered a risk to people or cats. Warts often go away on their own with time, and it is still worth having your vet confirm that a growth is a wart.

Lumps in rescued dogs

Rescued dogs often come with an unknown history and an estimated age, and lumps become more common with age. A female adopted as an adult may have gone through heat cycles before she was spayed, so her risk of mammary tumors may be higher than for a dog spayed before her first heat. Gently checking along her teats during grooming is a good habit.

At Paw Squadron, the first stops after every rescue are the vet and a bath, and every animal gets a checkup, treatment, vaccinations, and a microchip before adoption. A lump can still appear at any time, so it helps to point out anything new at your first visit with your own vet and to keep up regular checkups after that.

You can meet dogs looking for homes on our Adoptions page and find more health guides in PawPedia.