Sudden Lumps on Dog Under Skin: What It Could Mean

Finding a lump on your dog can be concerning, but it’s not necessarily a reason to freak out. Lumps on a dog can be a sign of underlying cancer, infection, or aging. Let’s talk about why dogs get lumps and bumps and which ones are a big deal.

Why do dogs develop sudden lumps on their skin?

Dogs can develop lumps for a variety of reasons, including insect stings, injuries, tumors, and infections. Occasionally, lumps can be identified based on physical appearance and the dog’s medical history. However, most lumps on your dog require evaluation by a veterinarian and diagnostic testing to determine the exact cause. 

Lumps on dogs can be benign or malignant. Benign lumps are non-cancerous. They may grow in size, but they don’t invade other tissues or spread to other parts of the body. Malignant lumps, on the other hand, are cancerous. They can invade nearby tissues, spread to other parts of the body, or cause harm to major organs. Many times, benign and malignant lumps on dogs can look very similar. 

Related article

Why Does Your Dog Have Bumps on Their Back?

Hmm, those weren’t always there...

Benign causes

Lipomas

Lipomas are benign tumors made up of fat cells. They’re common in older dogs and are often the reason senior dogs get “lumpy” with age. Dogs can have a single lipoma or develop many over time. Lipomas are typically soft and moveable under the skin, though they can feel firm if they develop beneath a layer of muscle, which is less common. Because lipomas are benign, they don’t invade the surrounding tissues; however, they can continue to grow until they cause issues. They can become a nuisance or impact quality of life if they grow in a location that interferes with normal movement, like in the armpit. 

Cysts

Two common types of cysts in dogs are sebaceous cysts and follicular cysts. Sebaceous (oil) glands produce sebum, which is a substance that helps keep a dog’s skin soft and their coat shiny. When the sebaceous glands become clogged, a sebaceous cyst can form. Similarly, follicular cysts can form when the hair follicle gets clogged with a protein called keratin. These cysts usually don’t cause any issues, but they can become infected if they rupture.

Hematoma

A hematoma is a pocket of blood underneath the skin. Hematomas can be the result of trauma or a bleeding disorder. If it’s secondary to trauma, the body will typically reabsorb the blood during the healing process. If a hematoma forms as a result of a bleeding disorder, treatment for the underlying issue is needed to prevent further blood loss. 

Abscesses

An abscess is a pocket of pus that forms under the skin, usually as the result of bacterial infection. If bacteria are introduced under the skin from a scratch or puncture, the body will respond by “walling off” the affected area and sending a ton of white blood cells (pus). Abscesses are often accompanied by fever and pain. They must be drained and cleaned for the infection to be cleared. 

Histiocytoma

Histiocytomas are benign growths commonly diagnosed in puppies. Histiocytomas tend to appear suddenly. They are small, raised, hairless, red lumps and are often described as “button-like”. Histiocytomas typically go away on their own over weeks to months. They are typically only of concern if they start bleeding, become infected, or don’t go away as expected. 

Malignant causes

Mast cell tumor

Mast cell tumors are exactly what they sound like — they are tumors of mast cells, which play a role when a dog has an allergic reaction. They are the most common type of skin cancer in dogs. Mast cell tumors can occur anywhere in the body and commonly develop on the limbs and trunk. They can vary widely in size and appearance. Mast cell tumors can be hairless, red, or ulcerated. They famously seem to wax and wane, sometimes  getting smaller and resolving on their own before returning. Mast cell tumors are more likely to develop in older dogs, but they have been diagnosed in young adults and puppies. 

Melanoma 

Melanoma is a cancer of the melanocytes, the pigment-producing cells of the skin. Melanomas commonly develop in the mouth or on the toes. They’re typically dark skin masses, but they can be pink as well. Malignant melanomas tend to grow quickly and be very invasive, spreading to other tissues, lymph nodes, and organs. 

Squamous cell carcinoma

Squamous cell carcinoma (SCC) is a cancer of the cells that make up the outer layers of the skin. These tumors often appear on areas of the body with less hair or pigment such as the belly, ears, nose, or eyelids. SCC is locally invasive. Chronic sun exposure may increase the risk of SCC in some dogs. 

Soft-tissue sarcomas

Sarcomas are tumors made up of connective tissue. Sarcomas range in severity, but they can be extremely invasive, fast-growing, and form a well-developed blood supply — all of which can make complete removal tricky. 

Lymphoma

Lymphoma is a cancer of the lymphocytes, which are a type white blood cell. In many cases, the first sign of lymphoma is enlarged lymph nodes, which can feel like firm lumps under the skin. The easiest-to-find lymph nodes on a dog are located under the jaw, in front of the shoulder blades, in the armpits, and behind the knees. 

Other potential causes

Skin infection or irritation

Skin diseases can lead to lumps and bumps on dogs. Skin irritation can cause papules to form. Papules are bumps that are firm and small (less than a centimeter). Pustules are also less than a centimeter but are the result of infection and are filled with pus. Nodules are pus-filled lumps that are larger than a centimeter, and they are usually a sign of deep skin infection. 

Allergic reaction

Allergic reactions can cause dogs to develop hives on their body. Hives are raised, red areas of the skin and tend to be itchy. Dogs can develop hives if they have an allergic reaction to insect bites/stings or other substances in their environment. 

Parasitic bites

Bites from skin parasites like fleas or mites can cause small bumps to form on a dog’s skin. This is especially true if a dog is both allergic to flea bites and has a large flea burden.

How do vets diagnose sudden lumps on a dog’s skin?

On rare occasions, your vet can look at your dog’s lumps and feel pretty certain about the origin. This is common when your dog gets stung by a bee and then develops facial swelling, itchiness, and hives (small lumps) all over their body. Your vet can say that the lumps are hives due to an allergic reaction to an insect sting with a high degree of certainty. Most other lumps require diagnostic testing, which often involves taking a simple from the tissue.. 

This may involve performing a fine-needle aspirate (FNA), which can be performed relatively quickly. To perform an FNA, a veterinarian will insert a needle into the lump and aspirate (remove) cells or fluid that is present. Then, the sample is examined under a microscope to determine the type of cells present. 

If a larger tissue sample is needed, or if a vet is concerned that a lump may be malignant, then a biopsy can be performed. A biopsy involves removing a chunk of tissue for evaluation by a pathologist in a laboratory. This is typically performed while a dog is under general anesthesia (because, ouch), but can sometimes be done with local anesthetic only. Many times, veterinarians will recommend removing the entire lump and sending the whole thing off for testing in hopes of limiting the process to only one procedure for your pup.

If there are signs of malignancy on initial testing, further testing may be needed to determine if the disease has spread to other parts of a dog’s body. Imaging such as radiographs or ultrasound is a common next step. 

Treatment options for dog lumps 

The treatment for a dog’s lump depends on the diagnosis and the impact it has on a dog’s quality of life. In general, there a few categories of treatment options for dogs lumps:

Surgical removal

Lump removal is typically recommended if the lump is malignant or bothersome. Some dog parents may also opt for removal for cosmetic reasons. Surgical removal for a large mass is performed under general anesthesia and best practice is to get “clean” margins, which means removing an additional two to three centimeters of tissue to make sure no abnormal tissue stays behind. Small lumps may be removed with local anesthesia or lasers.

Monitoring

Some dog parents may opt for a “wait-and-watch” approach to their dog’s lumps. This typically involves monitoring for changes in size, appearance, or comfort level. This is a common course of action for people with older dogs that have slow-growing lipomas or in cases where anesthesia is considered high-risk. 

Drainage

Drainage is an appropriate treatment option for fluid-filled lumps and not solid tissue masses. For example, drainage is part of the standard treatment for abscesses caused by bacterial infections. The fluid must be drained in order for the body to clear the infection. 

Medication

When a lump is related to a systemic issue, medication may be recommended to address the underlying cause. This is true for lumps secondary to allergic reactions or inflammatory disease. 

Related article

Lipomas in Dogs: Causes, Symptoms and Treatment of Fatty Tumors

Here’s why you (probably) shouldn’t worry.

What to do if your dog has a lump on their skin

If your dog develops a lump, don’t panic. A soft, non-painful lump that you happen to find during cuddle time doesn’t require a visit to the ER. In these cases, it’s fine to call your vet and set up an appointment for evaluation. In the meantime, make sure your dog isn’t constantly chewing or scratching the lump and that they’re normal otherwise. 

If your dog has a slow-growing lump that you’ve been monitoring and it suddenly changes, it should be evaluated by a veterinarian. If any lump is causing your dog pain or discomfort, or if your dog has additional symptoms, you should have the lump checked out by a veterinarian. 

When to see a vet

Most lumps aren’t medical emergencies, but many lumps are a sign that your dog needs attention. Seek veterinary attention if your dog’s lump:

• Is causing pain 

• Is bleeding or oozing

• Suddenly changes in size or appearance

• Interferes with normal activities

• Is obviously bothered your dog (constant licking or scratching)

• Is red, irritated, or ulcerated. 

• Is associated with itching and facial swelling and redness

• Appears after trauma or wounds

• Is accompanied by other symptoms like coughing, difficulty breathing, fever, lethargy, or poor appetite

Bottom line

Lumps on dogs can be either benign (non-cancerous) or malignant (cancerous). In most cases, collecting a sample of the lump for testing is needed to determine what type of lump a dog has. Treatment options can range from monitoring to medications to surgical removal. If your dog has a lump, especially one that appeared suddenly and is causing discomfort, it should be evaluated by a veterinarian. 

References

• Bray, Jonathan. “Soft Tissue Sarcoma in the Dog: An Update.” In Practice, vol. 40, no. 9, 19 Mar. 2018, pp. 383–395, https://doi.org/10.1136/inp.k707.

• Cohn, Leah, and Etienne Cote. Cote's Clinical veterinary Advisor: Dogs and Cats - E-Book. Available from: Elsevier eBooks+, (4th Edition). Elsevier - OHCE, 2019.

• ‌“Fundamentals of Surgical Oncology in Small Animals.” Today’s Veterinary Practice, 1 Nov. 2013, todaysveterinarypractice.com/oncology/fundamentals-of-surgical-oncology-in-small-animals/.

• “Tumors of the Skin in Dogs - Dog Owners.” Veterinary Manual, www.msdvetmanual.com/dog-owners/skin-disorders-of-dogs/tumors-of-the-skin-in-dogs.