Why Are My Dog’s Nipples Enlarged? Causes And Reasons For Alarm

Picture this: you are giving your fur baby a nice belly rub when you feel something unusual, like swollen and seems like ‘tender to the touch’ nipples. It’s alright to be alarmed, more so if it’s your first time to care for a female dog. Today, we’d share with you what it means if your female pooch has swollen nipples.

Dog nipples get enlarged usually during pregnancy and and heat cycles as the mammary glands around the nipples gets loaded with milk, a natural, biological and maternal reaction. The dog nipples can get red and swollen as result, which is totally natural during these periods. However, if your fur baby is not pregnant and the nipples are getting bigger, an infection can be the culprit.

Let us now understand deeply why your dog’s nipples are enlarged and under what circumstances should you be alarmed…

How Long Does A Dog’s Nipples Stay Swollen After Being In Heat?

Dog nipples usually stay swollen for up to 2 weeks before the swelling begins to subside.

It is not uncommon to see dogs with swollen nipples of different sizes, some pet owners observe that the 2 bottom nipples are typically more swollen than the others. This is a result of a normal heat cycle that begins with Proestrus, Estrus, Diestrus, and lastly the Anestrus.

How do you know if your dog is going into heat? First, your female pooch will get into heat between 6 to 15 months of age, with a majority of them having 2 estrous cycles each year. One of the common signs of a dog entering the heat cycle is swollen nipples. Let’s now look at the other symptoms for each stage of the heat cycle.


This is the start of the heat period wherein your dog’s body is being prepped up for possible mating. The proestrus stage normally lasts for 9 days, but for some, it may be as short as 3 days while for some dogs, maybe longer to up to 17 days

At this point, your female pooch won’t be showing any signs of interest in boy dogs, at least, not just yet. In fact, if a male dog attempts to get close to her, she’d respond in an aggressive manner.

The most obvious signs of proestrus stage are bloody discharge, licking of the genital area, increased food intake, and a clingy behavior.


This is the stage wherein your female pooch is ready and receptive to mating. On average, the estrus stage lasts between 5 to 10 days.

During this time, the bloody discharge lessens and stops eventually. The nipples begin to enlarge or get swollen, and so is the genital area. Changes in the sizes of the nipples and the vulva are due to the elevated levels of progesterone.

It is also the progesterone that intensifies the effects of estrogens in your female dog’s brain to demonstrate outward signs of heat such as tail flagging and frequent urination as a form of marking.


After the ‘in heat’ period’ comes the diestrus stage wherein your dog’s body proceeds with the pregnancy after successful mating. If not, her body will take a rest for an average of 2 months. This is the time when the vulva returns to its normal size and the swollen nipples begin to shrink.

Once all the swellings and discharge have disappeared, the heat cycle is ‘officially completed’.


Also referred to as the ‘repair or the resting phase in the heat cycle’. This is the longest stage in the cycle that lasts an average of 100 to 150 days, at the end of which, the heat cycle begins again.

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Does Enlarged Nipples Mean A Dog Is Pregnant?

Most of the time, dogs with enlarged nipples are pregnancy. Along with enlarged and discolored nipples, the other indications that your dog is pregnant are decreased activity, change in appetite, unusual behavior, weight gain, and nesting behaviors.

Enlarged And Discolored Nipples

The development of enlarged or pregnant dog nipples is one of the signs of early pregnancy. A female dog’s nipples are usually small but when it becomes pregnant, her nipples will grow and become raised and noticeable.

After successful mating, you’d notice the enlargement of nipples to begin around 2 to 4 weeks and will continue to swell until it gives birth. Apart from growing bigger, her nipples will also turn darker as a result of increased blood flow.

Decreased Activity

Do you notice that your pooch is sleeping a lot? Lethargy and increased tiredness are the other signs of early pregnancy. So much is going on in her pregnant body so it’s normal if she does not show any interest in her usual activities such as playing fetch.

However, we do not recommend that you totally stop her exercise regimen, just take it slow so her body remains fit, healthy, and ready for the birth of her puppies.

Change In Appetite

The appetite of your pregnant pooch fluctuates depending on the stage of pregnancy. During the early part, you could see her eating less and may also vomit frequently, which is the canine equivalent of morning sickness.

Towards the middle stage of her pregnancy, her appetite increases, so you should gradually increase her food intake around the 5th week of pregnancy.

Unusual Behavior

A lot of pregnant dogs become more clingy and affectionate, seeking more attention and increased cuddle time from their human families. On the flip side, some of them may display the opposite, preferring to be by themselves, being distant and withdrawn.

These are normal behaviors that are triggered by their fluctuating hormones.

Weight Gain

As your pooch’s pregnancy progresses, you’d observe a significant increase in its weight along with her larger abdomen. If you touch her tummy, you may also feel some movements from her growing puppies.

Nesting Behaviors 

Your pregnant pooch will let you know if she is about to go into labor through nesting behaviors. She’d begin to shred newspapers and gather materials like blankets and pillows to build a nest for her puppies.

At this time, your pooch may become more irritable and restless as it is preparing itself to give birth and to nurse her puppies.

At about 3 to 4 weeks after birth, the puppies’ weaning process should begin. And, one week after weaning, the enlarged nipples should slowly go back to their normal size because milk production is gradually decreasing. For some dogs, the sizes of their nipples may shrink but they will not likely return to the same size as before.

Image from Majestic Pet Products

Why Are My Dog’s Nipples Swollen But Not Pregnant?

False or phantom pregnancy is one reason why your dog has swollen nipples, even if she is not pregnant, which is fairly common among unspayed female dogs. It is so common that an estimated 50% to 70% of female dogs will experience false pregnancy in their lifetime.

Before we discuss the symptoms, let’s first talk about why false pregnancies happen.

The main cause of false pregnancy is that after the heat season, hormonal changes happen in the body as a preparatory step towards possible pregnancy, even if fertilization did not happen or was not successful.

This comes naturally to dogs to help nurse the growing pups. If a number of dog aunts in the pack undergoes false pregnancies and produce milk, more pups will be nursed and have a high chance of survival in this way.

The symptoms of false pregnancy usually last from 1 week to a month. There are physical and behavioral signs that your pooch may be going through a phantom pregnancy.

Physical Signs 

The signs of false pregnancy are commonly seen within 4 to 8 weeks after the heat season.

One of the common signs is swollen nipples or the enlargement of the mammary glands. The swollen nipple glands also produce a serum that looks like breast milk only less viscous and lighter.

The other physical signs of phantom pregnancy are pretty much the same as an actual pregnancy. These signs are loss of appetite, swollen belly, and weight gain.

Behavioral Signs

Along with the physical changes that come along with false pregnancy, behavioral changes are also observed.

If your pooch is going through it, you’d see her acting as if she has puppies. She’d collect soft objects like stuffed toys, socks, and blankets and then collect these things in her favorite nook. Watch out because she will guard, protect, and nurture these things with all her might.

Do not bother her because at this point, she believes that these things are her puppies. She can be aggressive if she perceives threat.

What Should You Do About False Pregnancy?

As we’ve said, swollen nipples are the signs of false pregnancy, so you should focus on addressing this issue. Swollen mammary glands and milk production can cause your pooch to lick her nipples until they turn sore. Unfortunately, this leads to more milk production and possibly, an infection.

To stop excessive licking of the mammary gland, an Elizabethan collar or a shirt can be used to control licking. But, don’t worry because this, too, shall pass in 1 to 4 weeks.

Image from Majestic Pet Products

Can Dogs’ Nipples Get Infected?

Yes, the nipples of your dog can get infected.

Some of these health issues are mastitis and mammary cancer. Pyometra is another condition that can occur after the heat season.


Mastitis is an infection that affects the breasts of your female pooch. If you have a lactating female pooch and you see that her nipples are swollen, chances are high that she has mastitis. In addition to swollen mammary glands, the nipples become discolored, pretty much like a bruise. 

Also, if you see some pus or blood oozing out from her teats, you shouldn’t discount the possibility of mastitis infection. Avoid touching the mammary glands (unless you’d apply warm compress) and do not give belly rubs because mastitis is a very painful condition. 

Mastitis happens when the mammary glands become inflamed as a result of bacterial infection or accumulation of milk. The bacteria enters the glands through the teats and causes an infection. Other times though, there is no bacteria infection, rather, mastitis happens as a result of accumulation of excess milk in the mammary glands.

Once diagnosed, treatment includes oral antibiotics or anti-inflammatory medicines. But, if excessive milk is the cause, you can help ease the pain by gently massaging her mammary glands to express the excess milk. Applying warm compress 4 to 6 times every day is also recommended to keep the dog’s nipples clean.

Mammary Cancer 

Another health issue that causes the nipples to get swollen is a mammary gland tumor where there is a growth of a mass near the nippples. This condition can be likened to breast cancer in humans.

Mammary glands problems like cancer are common among intact and unspayed dogs because the hormones during the heat cycle can cause abnormal growth.

The tumor can either be soft or hard that eventually develops into an abscess. Not all tumors are cancerous, the benign usually takes a longer time to grow and has a smooth texture. On the one hand, if it’s a malignant tumor, the growth is rapid and has an irregular shape.


This medical condition is a serious threat to the life of your female dog. It is more common among those who have not given birth and occurs 4 to 6 weeks after her heat season. Pyometra happens if there is an infection in the uterus.

For the open pyometra, her cervix is relaxed and she will have a foul-smelling vaginal discharge. For the closed pyometra, the pus is trapped inside the uterus causing abdominal swelling.

If left untreated, the uterus will rupture and the female dog will develop high fever, rapid heart rate and sepsis, leading to fatality in severe cases.

Image from Best Bully Sticks
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Pete Decker