I Found Sudden Lumps Under My Dog’s Skin: What Now?

8 min read

Updated - Feb 9th, 2023

Key Points

  • A lump under your dog’s skin can be caused by many different factors – not just cancer. 
  • After finding a lump or bump, pet owners should consult their vet for a proper diagnosis. 
  • It’s important to continuously monitor sudden lumps under dog skin, checking their size and shape.

You’re petting your dog and showering them with love – when suddenly, you feel a suspicious new lump underneath their skin. Your first reaction might be to panic as a thousand questions run through your head: Can it be cancerous? Has it been there for a long time? Does it look like my dog is in pain? 

Discovering sudden lumps under dog skin can be a frightening experience, and moments like this remind us that – just like humans – dogs can get sick, too. The last thing you want is for your fur-ever pal to go through an unexpected health issue. However, there are various reasons for lumps and bumps, and many of them aren’t life-threatening. 

Here, we’ll walk you through some common symptoms, causes, and diagnoses associated with  sudden lumps under dog skin. At the end of the day, it’s crucial that you schedule an appointment with your vet and get more detailed information, as every case is different. 


After you find the lump, assess your dog’s body to see if there are any more lumps that you didn’t catch. Sometimes, bumps and lumps are so slow-growing so they’re difficult to notice. Dr. Jamie Whittenburg (DVM) explains, “All masses grow from just a few microscopic cells into larger masses that may be felt on the dog. A ‘sudden’ appearance of a mass or lump may be the owner just finding the mass for the first time, a very aggressive cancer, or even a cyst, seroma, or abscess filling with fluid.” 

When you notice a bump under your dog’s skin, follow these steps:

  • Feel the bump with your fingers. Is the bump soft or hard to the touch? Is it dry or oozing fluid? Make sure to take note so you can relay these details back to your vet.
  • Measure the size of the bump. Take accurate measurements of your dog’s bump, especially if you think it appeared out of nowhere. That way, when you meet your vet, you can have it measured again to see if there was any abnormal growth.
  • Take note of the bump’s color and texture. Though it might be difficult to assess the physical appearance of a bump if your dog has long fur, try your best to take note of any discoloration or strange skin textures.
  • Monitor for other abnormal symptoms. Aside from the bump, is your dog eating and drinking normally? How is their temperament? If anything seems out of the ordinary, bring it up to your vet during your visit.
  • Contact your vet as soon as possible. There’s no way to get a proper diagnosis and treatment options without seeking medical expertise. After your initial observations, call your vet and try to meet them sooner rather than later. Although there’s a good chance your dog’s bump is benign, you don’t want to wait to find out. 

Causes of lumps under dog skin

There are several reasons for sudden lumps under dog skin – some are non-life threatening, while others more critical. Factors like age, weight, and breed can have an effect as well. Below are several common types of lumps: 

Warts: Caused by the papillomavirus, warts are common in dogs that don’t have strong immune systems. They resemble small cauliflowers and can either go away naturally or be surgically removed. Keep in mind that warts are contagious between dogs, so if you have another puppy family member, it may be safe to separate them temporarily.

Abscesses: Abscesses are swollen infections where puss accumulates underneath the skin. They can be caused by an animal or insect bite. They can be painful for your dog if not treated promptly, especially if they burst. Your vet may prescribe antibiotics to curb serious infection. 

Hives: Like people, dogs can get small, bumpy hives due to an allergic reaction. These bumps may get very itchy and swell due to scratching.

Skin tags: When cells like fibroblasts overreact, they can cause your dog to grow extra skin that might look like sudden bumps. Most of them are harmless, but visiting the vet is the best way to give yourself peace of mind. 

Lipomas or fatty tumors: “The most common benign growth on dogs is likely the lipoma. These are squishy, moveable masses under the dog’s skin comprised of fat cells,” says Dr. Whittenburg. “They are more common in more senior dogs and overweight dogs, but may affect any dog. Unfortunately, these masses are not always benign and can be liposarcomas, which are cancerous and aggressive.”

Sebaceous cysts: Sebaceous cysts can look similar to warts, as they’re small, pimple-like bumps that form due to clogged oil glands. Breeds like the Poodle or the Bichon frise are more likely to develop these types of cysts.

Histiocytomas or button tumors: Histiocytomas are abnormal growths that take on a red, bubbly appearance. They mainly affect young pups that are anywhere from a few months to three years of age.

Mast cell tumors: Mast cell tumors in dogs are cancerous masses that can grow anywhere on a dog’s body. They vary in size and shape and can either be soft or hard. Because they have a chance of becoming more aggressive over time, it’s important to treat them as soon as possible.

Diagnosis of lumps under dog skin

Masses can either be benign or cancerous, but there’s no way of knowing without consulting your vet. If you notice sudden lumps under dog skin, the best course of action is to get a clinical diagnosis. 

“In general, cancerous masses grow more rapidly than benign ones,” says Dr. Whittenburg. “However, because there are so many different types of skin tumors in dogs, as well as different levels of aggressiveness, growth rate is not an accurate indicator of whether a mass is benign or malignant.” 

While a physical assessment might be the first step, your vet may need to conduct additional tests to narrow down the cause with a fine needle aspirate, biopsy, or other diagnostic method. 

What to expect at the vet

When it comes to identifying skin lumps, time is truly of the essence. “Waiting to see how a lump behaves may delay treatment until it has had a chance to spread, becoming a much more serious, even fatal, medical issue,” says Dr. Whittenburg. 

In other words, the faster you meet with your vet, the sooner your dog can receive the treatment they need to get better.  

When you meet with your vet, they may perform a simple physical examination, take blood work, and ensure that your dog isn’t presenting other concerning symptoms. Then, they’ll likely take additional tests, such as a: 

  • Fine needle aspiration: Your vet may use a syringe and small needle to pull cells directly from the bump and have them examined by a veterinary pathologist.
  • Biopsy: This test requires your dog to be sedated or under some form of anesthesia. Depending on your dog’s case, your vet may take a small sample of the mass or remove it entirely.
  • Ultrasound: An ultrasound might be helpful in getting a clear picture of the bump and determining whether it’s impacting your dog’s internal organs.
  • X-ray: If your dog has cancerous lumps, an X-ray can help determine whether the cancer has spread to other body parts.

The treatment for lumps on dogs varies widely. Whether your fur baby has to undergo a surgical removal, chemotherapy, or take prescribed medication, communicating with your vet will help you understand your dog’s health condition — and how you can help them recover, one step at a time. 

The bottom line

Sudden lumps under dog skin are alarming for any pup parent, but acting quickly can help alleviate worries and allow you to form a plan. Continue to keep a careful eye on the mass; you can even keep a log of your observations. Take a deep breath, acknowledge that these situations are scary, and remember that you’re not alone. 

Tip: Pumpkin Pet Insurance plans cover up to 90% of eligible vet bills for conditions like skin infections, cancer, and more. Protect your pup’s health get a free quote today


What causes sudden lumps under dog skin?

There are several reasons why your dog may develop bumps and lumps. It can be a benign growth, skin infection, allergic reaction, or something more serious like cancerous tumors. Consult with your vet to get an official diagnosis and treatment plan. 

Are cancerous lumps hard or soft? 

Compared to a lipoma, which can feel squishy and fatty, cancerous lumps are typically more firm to the touch. 

What is the difference between a lipoma, a cyst, and a skin tumor?

A lipoma is considered harmless and often slow-growing. A cyst is caused by a blocked oil gland and can rupture if not treated properly. A tumor can either be benign or malignant. Dr. Whittenburg notes, “Cancerous masses may be rapidly growing and therefore seem to appear suddenly. Though some benign masses tend to be slower growing than aggressive cancers, this is not an accurate way to identify a benign versus cancerous mass as many cancers have different behaviors and rates of growth.”

What are the signs of a mast cell tumor?

Mast cell tumors can look like a raised bump on your dog’s skin. Tumors vary in shape, size, and texture, depending on their chemical makeup. Keep in mind that touching a cancerous tumor can worsen your dog’s symptoms. 

What is the treatment for lumps or bumps on dog’s skin?

Treatment options for sudden lumps under dog skin depend on the cause of the lump. It’s best for concerned pet parents to talk to their vet to determine the best path forward. 

Did you know?

  • Some skin bumps are more common in older dogs or young pups. 
  • Waiting to see how a bump develops can be dangerous for your pet, so it’s important to get them seen by a vet asap. 
  • A swift vet visit can make a significant difference in your dog’s diagnosis, treatment, and recovery – and is therefore our strongest recommendation for any unexpected lumps and bumps underneath their skin. 

  • https://www.petmd.com/dog/symptoms/lumps-bumps-and-cysts-dogs
  • https://www.imprimedicine.com/blog/lumps-on-dogs
  • https://www.hillspet.com/dog-care/healthcare/types-of-lumps-on-dogs

Shi-won Oh

Shi-won is a copywriter and an enthusiastic dog aunt to Maltese and Shih Tzu puppies.
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