Why Are My Dogs Nipples Popping Out?

What are canine nipples?

Canine nipples are located on the underside of a dog’s belly on both male and female dogs. Female dogs typically have between 8-10 nipples, while males have 8-10 nipples arranged in two even rows from chest to groin area.

The purpose of canine nipples is to deliver milk to nursing puppies. Behind each nipple is a mammary gland which produces milk after pregnancy. The nipples extract the milk from the glands which the puppies drink for nourishment.

The anatomy of canine nipples is similar to human nipples. They contain small openings at the tip which extract milk from the mammary glands. The nipples protrude slightly from the skin and become swollen and enlarged during pregnancy and nursing due to increased blood flow.


When are protruding nipples normal?

Protruding nipples can be normal in female dogs during certain times, such as:

During heat cycles and pregnancy – A dog’s nipples will often become enlarged and protruding during estrus cycles as her body prepares for potential pregnancy and nursing. According to Dogster, nipples grow up to 1⁄2 inch during pregnancy.

While nursing puppies – It’s very common for a mother dog’s nipples to protrude significantly while she is nursing puppies. The nipples enlarge and protrude to allow the puppies to easily latch on and nurse. The nipples will likely shrink down after weaning.

In puppies and young dogs – Puppy and adolescent dog nipples may protrude more than normal until the dog matures. Protruding nipples in young dogs usually resolve as the dog grows.

Causes of abnormal nipple protrusion

There are several potential causes of abnormal nipple protrusion in female dogs:


Pseudopregnancy is a common cause of nipple protrusion in intact female dogs. It occurs after an estrus (heat) cycle when progesterone levels remain elevated, causing the female’s body to think she is pregnant. The nipples enlarge and mammary glands swell as they prepare for nursing puppies that do not exist. Pseudopregnancy usually resolves on its own within 2-3 weeks.1

Hormonal imbalances

Abnormal levels of estrogen, progesterone, prolactin, or other hormones can also cause nipple enlargement and swelling. Hormone imbalances may be caused by issues with the ovaries or adrenal glands. Diagnostic testing can identify the underlying cause, and treatment usually involves medications to restore hormone balance.


Mastitis is inflammation and infection of the mammary glands. It causes swelling, pain, and often discharge from the nipples. Mastitis requires prompt veterinary treatment with antibiotics, anti-inflammatories, and warm compresses.2

Breast cancer

Though less common than in humans, dogs can develop malignant mammary tumors. Cancer often appears as swollen, misshapen, or ulcerated nipples. Any abnormal nipple changes, especially in older female dogs, warrant veterinary evaluation to check for cancer.

Allergic reaction

Allergies to foods, insect bites, or other environmental triggers can cause itchy, swollen skin and nipples. Dogs may excessively lick or scratch at their breasts. Treatment involves removing the allergen and providing symptomatic relief.


Pseudopregnancy, also known as false pregnancy, is a hormonal condition that mimics pregnancy in unspayed female dogs. It occurs about 2-3 weeks after the dog goes into heat and can last for 2-3 weeks (1).

The condition is caused by hormonal imbalances after the progesterone levels drop following the end of the heat cycle, which triggers the release of prolactin. This leads to symptoms like swollen mammary glands, milk production, nesting behaviors, mothering inanimate objects, lethargy, vomiting, and abdominal enlargement (2).

While pseudopregnancy may resolve on its own, treatment usually involves resolving the hormone imbalance. This may involve medications prescribed by a vet to suppress lactation and other symptoms. Spaying the dog is also an effective long-term solution. Pseudopregnancy is not dangerous on its own, but dogs should be monitored for complications like mastitis (3).

Hormonal imbalances

Various conditions like thyroid disease or adrenal disease can cause hormonal imbalances that lead to abnormal nipple protrusion in dogs.

The vet will need to run testing like a full thyroid panel or an ACTH stimulation test to diagnose the specific hormonal imbalance. Treatment usually involves medications like thyroid hormone replacement or corticosteroids for adrenal disease.

Supplements may also help balance hormones, but should not replace prescription medication prescribed by the vet. It’s important to identify and treat the underlying condition causing the hormonal imbalance.


Mastitis is a bacterial infection of the breast tissue that causes swelling, pain, and discharge from the nipples [1]. It usually occurs in female dogs who are nursing new puppies. The mammary glands become inflamed, hot, and painful as infection sets in. There may be a watery or pus-like discharge from the nipples as well.

Mastitis is typically caused by a bacterial infection, most commonly by staphylococcus or streptococcus bacteria, which enters through cracks or wounds in the nipple skin [2]. It can develop from blocked milk ducts or trauma from the puppies’ suckling. Older female dogs may also get mastitis as their mammary glands involute after weaning.

Treatment for mastitis involves antibiotics to clear the bacterial infection along with anti-inflammatory medication to reduce swelling and pain. Puppies may need to be weaned early to allow the mother’s breasts to rest and heal. Severe cases may require surgical drainage or removal of the affected mammary glands. Prompt veterinary care is important for treating mastitis in dogs.

Breast Cancer

Breast cancer in dogs is a rare but aggressive type of cancer that affects the mammary glands. While not common, it is one of the most frequent cancers seen in female dogs that have not been spayed. Dogs with breasts cancer often develop lumps, swelling, and discharge from the nipples (VCA Hospitals, 2022).

There are various treatments available for canine breast cancer including surgery, chemotherapy, and radiation therapy. The prognosis depends on how early it is detected and how far it has spread. Like in humans, early detection gives the best chance for successful treatment. It is important for dog owners to routinely check their dog’s breasts for any abnormalities and see the vet if any lumps, skin changes, or discharge from the nipples are noticed (Blue Cross, 2023).

Some of the signs of breast cancer in dogs include (Atlantic Coast Vet, 2022):

  • Lumps or bumps around the nipples
  • Swollen or painful breasts
  • Bloody or pus-like discharge from the nipples
  • Ulcers or skin changes on the breasts

While scary, breast cancer in dogs can often be treated successfully if caught early. Being vigilant about checking a dog’s breasts and any changes is critical. If any abnormalities are found, make an appointment with the vet right away.

Allergic Reaction

Exposure to allergens can sometimes cause the nipples and surrounding skin to become swollen and irritated. Dogs have sensitive skin, and allergens like pollen, flea bites, certain foods, and chemicals can provoke an allergic reaction. The main symptom is itchy, red, swollen skin and nipples. There may also be hives or small bumps. According to this veterinary source, allergic reactions are one of the most common causes of nipple irritation and swelling.

The best treatment is identifying and removing the allergen that is causing the reaction. Your vet can help you figure out what your dog may be allergic to. They may recommend an elimination diet or allergy testing. Topical hydrocortisone creams can help reduce inflammation and itching. Antihistamines may also be prescribed to control the allergic response. The swelling and irritation should go away once exposure to the allergen stops.

When to see the vet

If your dog’s nipples remain extended or protruding for more than a few days after their heat cycle ends, it’s a good idea to make an appointment with your veterinarian. According to PawSafe, enlarged nipples that persist could signify an underlying health issue like a hormonal imbalance or tumor.

You should also see your vet if your dog’s nipples seem painful, swollen, or are oozing any kind of discharge. These can be signs of a more serious condition like mastitis or a mammary tumor. Your vet can help diagnose the cause and prescribe any necessary treatment.

It’s also a good idea to take your dog to the vet if she seems lethargic, is eating less, or generally seems unwell. Changes in behavior along with nipple abnormalities could indicate she’s not feeling well for some reason. Your vet can give your dog a full exam and determine if her symptoms are related.

In most cases, a quick vet visit can identify the cause of protruding nipples and rule out any serious underlying problems. Early evaluation and treatment greatly improve the chances of a full recovery. Don’t hesitate to call your vet if your dog’s nipple issues persist or worsen. They can provide an accurate diagnosis and appropriate treatment plan tailored to your dog’s specific condition.


There are some steps dog owners can take to help prevent abnormal nipple protrusion in their dogs:

Spaying or neutering dogs at an early age can help prevent hormone-related causes like pseudopregnancy according to [URL1]. The hormones from heat cycles and intact reproductive organs can lead to nipple changes.

Keeping your dog free of skin allergies through good nutrition and grooming can prevent allergic reactions that lead to nipple swelling per [URL2]. Check for any skin irritation during regular brushing and bathing.

Examine your dog’s nipples regularly during grooming and petting for any abnormalities recommends [URL3]. Early detection of changes allows for quicker veterinary diagnosis and treatment if needed.

Annual veterinary exams provide an opportunity for professionals to inspect your dog’s nipples and identify any issues. Routine wellness checks lead to early diagnosis of potential problems.

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