Lumps Under Dogs Nipples After First Heat


If you own a female dog, you may already be familiar with some of the signs and changes associated with a dog’s heat cycle. During the heat cycle, a dog’s breasts may swell and become sensitive, among many other changes. 

But what if they have lumps under the nipples, or swollen nipples after heat, is that also normal?

In some cases, lumps under the nipples of an intact female dog might be associated with the heat cycle and would disappear a few weeks after heat, this is known as mammary gland hyperplasia. 

Let’s further explore what swollen nipples after heat and lumps under a dog’s nipples could mean…

Is it normal for dogs to have swollen nipples after heat?

The nipples and mammary glands in dogs typically do not enlarge at the peak of the heat cycle. However, when the heat cycle is almost complete and the progesterone levels are at their highest, you might observe a notable enlargement in your dog’s nipples and breasts.

During the heat cycle, your dog’s body experiences several hormonal changes, all of which may trigger a small enlargement of the nipples and mammary glands.

Female dogs tend to feel stressed when in heat, and as a result, the vulva and nipples are licked excessively, which also contributes to their swelling.

If your dog appears to be in good health and exhibits other typical signs of being in heat, you shouldn’t be concerned if you notice a sudden increase in the size of their nipples.

After the heat cycle, a dog’s nipples often remain swollen for 2 to 3 weeks before returning to normal on their own. Except, if they are experiencing a pseudo-pregnancy, in which case the nipples will remain swollen for much longer (up to 9 weeks).

Another thing to consider is actual pregnancy. It’s possible that your intact female dog is currently pregnant, if she mated while in heat. Your dog’s nipples and breasts will get larger within the first two weeks of mating, as this prepares her body for milk production.

Typically, it takes a couple of weeks for heat-related changes in a dog’s nipple to resolve, therefore it may not be necessary to take her to the vet right away.

What are the symptoms of a female dog in heat?

Having an understanding of a dog’s heat cycles and the changes that come with it will help you to better prepare for what to expect and how to care for your dog during this period. 

You will notice different changes during each phase of her heat cycle, and depending on the stages, you will notice the following signs;

  • Enlarged vulva
  • Change in tail position
  • Bloody discharge coming from the vulva
  • Friendly to canine males
  • Genital licking that is excessive
  • Aggressive, agitated, or nervous behavior
  • Urinating more often

What age do most dogs experience their first heat?

The age at which a dog has her first heat cycle varies considerably by breed. While large breeds may take up to 2 years to reach their first heat cycle, toy breeds can reach their first heat cycle as early as 4 months. Most dogs have their first heat cycle between the ages of 6 and 15 months.

Can nipples become swollen in young female dogs that have been spayed?

Yes, this is possible if the female dog has an infection or inflammation of the breast tissue. Swollen nipples are a common symptom of mastitis in dogs. Mastitis is typically caused by a bacterial infection, although it can also be caused by fungal infections of the breast.

An injury to the mammary gland can make it possible for microbes to get inside the breast tissue and cause inflammation. Staphylococcus, E. coli, and Streptococcus are the most common microorganisms that cause mastitis.

Why does my female dog have lumps on her breast?

There are quite a few reasons why a female dog will have lumps in her nipples, and here are the most common ones;

  • Mastitis
  • Mammary gland tumor
  • Mammary gland hyperplasia

Mammary gland hyperplasia: Mammary gland hyperplasia is a condition in which the mammary glands of an intact female dog form lumps during the heat cycle. It’s caused by high levels of progesterone and happens within 1 to 2 weeks after the estrus stage of the heat cycle. The lumps disappear as the hormone levels associated with the heat cycle reduce.

Mastitis: swollen or lumpy nipples are a common symptom of mastitis in dogs. Dogs with mastitis experience painful swelling of their mammary glands. It happens when the mammary glands become infected. Mastitis is most commonly seen in nursing dogs. 

Mammary gland tumors: Breast lumps can be an indication of mammary tumors. These tumors are most common in dogs who have not been spayed or who were spayed after their second heat cycle.

Can a female dog get mastitis without being pregnant?

Mastitis can affect dogs who have never been pregnant, but it most frequently affects dogs who have recently given birth. Dogs experiencing pseudo-pregnancy can also develop mastitis.

Female dogs who have not been spayed may have pseudo-pregnancy, also known as false pregnancy, in which they exhibit pregnancy-related signs like the growth of their breasts and lactation without actually being pregnant. 

Mastitis is often caused by a bacterial infection, but it can also happen in the absence of an infection. Mastitis caused by bacteria occurs when the bacteria enter the mammary glands through the nipples. 

Dogs who live in a dirty environment or have injuries to the nipples or mammary tissue have a higher risk of developing breast infections. Mastitis is also caused by a fungal infection.

This condition can be very serious and should be treated quickly in order to stop the infection from spreading and further inflaming the breast tissue.

If your dog is found to have mastitis, your vet might recommend antibiotics and NSAIDs for pain management.

Lumps can be a sign of mammary tumors in dogs

A mammary gland tumor is another possible cause of lumps or swollen nipples in a dog, and female dogs are more likely to develop mammary gland tumors than male dogs. A mammary tumor forms as a result of abnormal cell replication in the breast tissue.

A lump that is located close to the nipples is a sign of a mammary gland tumor. The tumor may be either soft or hard, and it has the potential to become an abscess. Mammary gland tumors can either be benign or malignant, and they vary in size, color and location. 

Benign (non-cancerous) tumors often develop slowly and have a smooth texture, while malignant (cancerous) tumors typically grow much faster and tend to have an uneven form.

Only about 0.5% of dogs who are spayed or neutered before their first heat will develop mammary cancers. However, this rapidly rises to a risk of 8% after the first heat and jumps to 26% after the second heat.

Age also seems to be a risk factor; as a dog reaches 7 years of age, the risk of tumor growth considerably increases and remains high until 11–13 years of age. Genetics and breed type are also factors that contribute to the risk of mammary gland tumors in canines. 

How do I know if the lump on my dog is a tumor?

The most typical clinical symptom of benign mammary tumors is one or more lumps that you may feel under the skin of your dog’s lower chest or abdomen.

These lumps can be found along the mammary chain, within or next to the nipple. Dogs have 5 pairs of mammary glands on their chest and abdomen, it starts just below the armpits and runs down to the groin. The mammary glands make up the mammary chain.  The size and appearance of the lumps can vary, but they are often firm and nodular, and are usually not painful.

Can breast lumps in dogs dissolve on their own?

It’s not advisable to ignore a tumor with the hope of it dissolving on its own, because dogs with benign mammary tumors are more likely to develop malignant tumors. And it is believed that benign tumors potentially lead to malignant ones, although some benign tumors may remain small and benign for as long as they last.

While other benign breast tumors may grow, generate new tumors in fresh spots along the mammary chain, and turn malignant. The best chance for long-term tumor control is to find and treat these tumors while they are still small and haven’t spread. Hoping that they dissolve on their own is not a good management option for mammary tumors. 

What does a mammary tumor look like on a female dog?

Dogs have ten teats or nipples. A growth around one or more of the nipples is referred to as a mammary gland tumor.

Tumors might show up as a soft or hard lump in the breast, they can be red, purple or the same color as your dog’s skin. These lumps are initially covered with hair and skin, and as they progress they may form an abscess, burst open and bleed. 

Since canine mammary tumor usually affect female dogs, it is necessary for dog owners to constantly inspect the mammary area for lumps. Cancer and tumors of the mammary gland are particularly common in female dogs, and early detection is important as it determines the success of the treatment.

How common are mammary tumors in dogs?

Dogs frequently develop mammary tumors, and half of these are cancerous. Intact female dogs are more likely to develop mammary cancers, than spayed female dogs. In fact, spaying a dog before the first or second heat cycle greatly lowers the chance of mammary tumor development in dogs.

Overweight dogs that are fed a high-fat diet have a higher risk of developing mammary tumors. 

If you discover a lump on or around your dog’s nipples or anywhere along the mammary chain, endeavor to have her promptly examined by a vet, especially if she is intact.

After each heat cycle, some intact female dogs may develop lumps that come and go. These are often caused by rapid growth of the mammary tissue, and referred to as mammary gland hyperplasia.

How do you get rid of mammary tumors in dogs?

Surgery is by far the best option for treating canines with mammary tumors. If your dog only has a single small lump with no sign of spread, then the tumor is surgically removed. However, if a dog has multiple tumors along the mammary chain, then all the affected breast tissues will be removed. 

Sometimes, an entire mammary chain or both are removed, depending on the severity and amount of spread. And if the dog is intact, she will be spayed during the surgery. Whether a tumor is benign or malignant, early detection with prompt and appropriate treatment offer the best chance of a full recovery.