Female Dogs In Heat: What They Look Like [Pictures & Vet Info]

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female dog in heat with a diaper on

This article was updated on October 30th, 2023

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You may be prepared for the bleeding that will accompany your dog’s first heat cycle, but there are other bodily changes that might come as a surprise. When your dog experiences their first heat cycle, between six and eighteen months of age, you may also notice a dramatic swelling of the vulva.

The term “in heat” is used to describe the time in a female dog’s reproductive cycle when she is receptive to mating and able to conceive. The true term for this period of her cycle is called estrus. During this time, there are multiple surges and drops of her hormone levels, which have varying effects on her body.

Read on to learn more about what to expect when your female dog is in heat. You will also find a few pictures of swollen female dogs to help you understand what is normal, and when you might need to call your vet.

beautiful white Samoyed dog in classy living room by the couch

What does a female dog look like when in heat [with pictures]?

Whether or not you have ever owned an intact (unspayed) female dog, you likely are familiar with the idea that a dog in heat will have bloody vaginal discharge. What you may not know, however, is that your dog’s vulva will also swell significantly when they are in heat. This is a normal finding, and it’s caused by the effects of estrogen on your dog’s reproductive tract.

A swollen vulva is often one of the first signs that a dog is going into heat. The vulva will remain enlarged throughout the dog’s fertile period, and then it will gradually decrease in size. It’s important to note, however, that your dog’s vulva may never return to the size that it was before her first heat cycle. Dogs that have had one or more heat cycles will often have a vulva that remains permanently larger than that of dogs spayed before their first heat.

In these 2 pictures below, you can see the appearance of a slightly swollen canine vulva, accompanied by a small amount of bloody vaginal discharge:

female dog in heat with bloody vulva discharge

This picture shows the swollen vulva of a dog in heat (on the right):

swollen vulva of a dog in heat

What are the visual characteristics of a swollen vulva of a dog in heat?

Some of the signs are subtle or behavioral in nature. However, there are also clear visual cues that indicate a dog is in heat. A dog that is in heat will often have visible swelling and enlargement of the vulva. Additionally, you may see bloody or blood-tinged vulvar discharge.

Signs your dog may be in heat:

  • Swelling or enlargement of the vulva
  • Bloody or blood-tinged discharge from the vulva
  • Urinating more often than usual
  • Licking at the vulva more often than usual
  • Increased mounting/humping behavior
  • Increase in anxious behavior
  • Roaming or increased interest in male dogs

Abnormal swelling in some dogs

Some dogs experience much more dramatic swelling of their vulva while in heat. Click here to see a picture showing a degree of swelling that may be normal in some dogs, but is likely abnormal or problematic swelling in most dogs.

Is my dog swollen because she is in heat, or is something else wrong?

While swelling of the vulva is a common sign of heat, there are also medical conditions that may cause an appearance that suggests vulvar swelling. It’s important to be able to distinguish between heat and these potentially-serious conditions.

1. Vaginitis

While a dog’s heat cycle is accompanied by vulvar swelling and bloody discharge, you may also notice inflammation of the vulva and a purulent (pus-filled) discharge if your dog has vaginitis. This condition is common in young puppies, but can also occur in adult female dogs. Vaginitis may also be accompanied by redness around the vulva.

Click to enlarge picture.

There are a variety of recommended treatments for vaginitis in dogs, depending on your dog’s overall condition and the severity of the vaginitis. See your veterinarian if you suspect that your dog may have vaginitis.

2. Vaginal hyperplasia

Vaginal hyperplasia is another condition that can cause swelling in the area of the vulva. In this condition, fluid-filled vaginal tissue prolapses from the vulva and is visible outside the body. This condition is most common in intact dogs and is associated with the effects of estrogen.

This picture may be shocking to some readers: click here to view.

If your dog has vaginal hyperplasia, they need veterinary care to prevent infection and injury to their prolapsed vaginal tissues. Your veterinarian will also likely recommend spaying your dog, to prevent future episodes of vaginal hyperplasia.

In some cases, vaginal hyperplasia can block a dog’s ability to pass urine. This is a life-threatening emergency and requires emergency veterinary care.

3. Rectal prolapse

In contrast to vaginal prolapse, rectal prolapse can affect both male and female dogs. In this condition, usually caused by gastrointestinal issues and/or excessive straining to defecate, a small amount of tissue prolapses from the rectum. Rectal prolapse is a medical emergency. Seek veterinary care immediately if you suspect rectal prolapse. Learn about about prolapse in dogs.

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When should you call your veterinarian?

Vulvar swelling is normal when a dog is in heat.

If you know that your dog is in heat and their vulva is mildly to moderately swollen, monitoring your dog at home is a reasonable option.

However, if your dog is demonstrating extreme swelling of the vulva or swelling that is occurring while they are not in heat, you should seek veterinary care. Your veterinarian will perform a thorough physical examination and diagnostic tests to determine the cause of your dog’s vulvar swelling and recommended treatments.

Can you prevent vulvar swelling during future cycles?

As long as your dog is experiencing heat cycles, you will continue to see episodes of vulvar swelling. The only way to prevent heat-related vulvar swelling is to have your dog spayed.

Fortunately, spaying your dog offers a number of additional medical benefits. Spaying your dog while they are relatively young can markedly decrease your dog’s risk of mammary (breast) cancer, a common health threat in dogs. Additionally, spaying your dog will prevent uterine cancer.

Talk to your veterinarian to learn more about having your dog spayed.

5 steps you can take at home to help your dog

Your dog’s heat cycle can be stressful for both you and your dog.

Consider the following steps to reduce your dog’s stress:

  1. Walk your dog during quiet times of the day. Male dogs will be attracted to your dog’s scent. Walk her when fewer dogs will be outside.
  2. Bathe your dog frequently to control odors. Most dogs will groom themselves to remove blood and vaginal discharge. Bathing your dog can help minimizing the amount of self-grooming that she needs to do.
  3. Distract your dog with play. If your dog appears restless or anxious, interactive play can help distract her from her heat cycle.
  4. Keep your dog on-leash and closely supervised. In order to prevent unwanted mating, it’s important not to allow your dog outside unattended.
  5. Have your dog spayed. If you do not plan to breed your dog, you should have her spayed to prevent further heat cycles.

Frequently asked questions

How often do dogs go into heat?

Most dogs go into heat every six months or twice yearly. However, some dogs may have as few as one heat cycle per year, while other dogs may have as many as three heat cycles in a year.

Is my dog in pain when in heat?

Being in heat isn’t painful, but it can cause some discomfort or restlessness. If your dog appears painful, consult your veterinarian. 

What do I do if my female dog’s vulva is swollen but she is not in heat?

If your dog’s vulva is swollen and you know that she is not in heat, contact your veterinarian. Your veterinarian will perform a physical examination and laboratory tests to rule out infections, tumors, and other problematic causes of vulvar swelling.

Do female dogs go through a menopause stage?

Dogs do not experience menopause in the way that we see in humans. A dog’s heat cycles may become less frequent with age, but they do not typically stop completely. Most dogs can become pregnant throughout their lifespan.


  • Dr Cathy Barnette

    Dr. Cathy Barnette has worked as a veterinarian in the United States for 14 years. She graduated in 2006 with a Doctorate in Veterinary Medicine (DVM) from the University of Florida. She lives in Florida with her family, two cats and one dog.

    View all posts

Disclaimer: This website's content is not a substitute for veterinary care. Always consult with your veterinarian for healthcare decisions. Read More.


  1. I have a 9 month old female chihuahua who is in heat. I also have a mastiff, German Shepherd, pit bull who weighs around 140 lbs. and is trying to mount her. Should I be worried?

    • Yes, there is always the potential for a mating and this is not a pregnancy that is advised, given the size difference. A c-section would be needed. We must keep them apart and I’d have one neutered ASAP to prevent any unwanted litters.
      Dr Linda Simon MVB MRCVS
      “The information on this website is not a substitute for in-person veterinary care. Always seek advice from your veterinarian if you have concerns about your pet’s medical condition.”

    • Hi there and thank you for this question.
      The inside tissue can be quite dark pink, red or purple. It is very vascular, meaning there are lots of blood vessels, which give it its color.
      However, this is not usually an area we would notice.
      If it is that you can see the tissue looks more red externally, it is swollen, she is licking at it or it has been bothering her, this likely indicates an issue such as a vaginitis, UTI or infection.
      In this case, she should see her vet who can examine the area and perhaps swab it for infection if concerned.
      It may be she needs e.g. some anti inflammatories.
      If she has been licking, we should prevent this by using a buster collar.

      “The information on this website is not a substitute for in-person veterinary care. Always seek advice from your veterinarian if you have concerns about your pet’s medical condition.”

    • Hello and thank you for your question!
      This is Dr Linda, one of the website’s vets.
      How long a season lasts depends on several factors including a dog’s age and breed. However, for most dogs their cycle will last around 3 weeks. Once your bitch has got an established routine, they should have regular heat cycles that are evenly spaced apart and last roughly the same time.
      They will not bleed for this entire time; most only bleed for around half of this time. Similarly, they are not fertile for this entire time.
      For most bitches, the vulva stops being swollen once the cycle has finished, so is swollen for about 3 weeks.

      “The information on this website is not a substitute for in-person veterinary care. Always seek advice from your veterinarian if you have concerns about your pet’s medical condition.”

      • I have called my veterinarian 4 times with questions about the heat cycle/ length of time. I keep getting the same response that it’s normal especially for the first time she’s had it. We noticed the drops of blood beginning December 22 and now we are on weak six and there still are a few drops of blood here in there. What is a length of time that really is normal?

        • Hi Laura and thanks for your question about your dog. A typical heat cycle will only last about 3 weeks, with the dog bleeding for about 10 days or so. However, there can be exceptions to this. Some dogs will bleed for longer and some will experience a ‘split heat’ cycle whereby they seem to come into season, but do not ovulate, and then come back in again fully. This can prolong everything.
          Having said the above, as it has been 6 weeks, I would schedule a vet check. They can assess your dog and check for any underlying issues such as a clotting disorder, UTI or vaginitis. They can also ensure she is not anaemic. By assessing her vaginal cells, they can determine at which stage of her cycle she is currently at, which will help us determine what exactly is going on.
          “The information on this website is not a substitute for in-person veterinary care. Always seek advice from your veterinarian if you have concerns about your pet’s medical condition.”

  2. I have a female golden retriever that has been exhibiting signs of heat since September 22nd, 2023. Today is October 19th and the symptoms aren’t improving. Her progesterone levels have been at a 1.2 for 3 weeks. Her vulva is swollen, she’s urinating quite a bit and my boy has been going crazy.. he sniffs and licks her as well as tasting her pee. She isn’t lethargic, and appetite is still good. I just don’t understand what’s going on. Help?

    • Hi there and thank you for your question. I’m sorry to hear you’ve been dealing with this issue, and can imagine it has been stressful given there is a male dog in the home.

      Given her signs, I would consider a vaginitis or UTI causing her frequent urination and swelling; this can be confused by the male for a bitch being in season even when they are not.

      Another consideration, if that Progesterone levels is measured in ng/ml, she may be experiencing a prolonged pro-oestrus. The level should rise as she ovulates.
      She may have a ‘persistent oestrus’ due to e.g. a hormonal imbalance, exposure to oestrogen (e.g. from a human in the home using certain medication), an ovarian cyst etc.

      It may also be that this is an anovulatory cycle. This is not common in females, but can occur, and they usually come into their next heat cycle earlier than expected.

      I’d use a buster collar to stop her licking her vulva if she is doing this.
      I’d also consider a vaginal swab for infection and urine analysis.
      If issues persist, it is worth consulting a reproduction specialist / endocrinologist who may perform vaginal cytology, some specific blood tests and a reproductive scan, to get a clearer answer.

      “The information on this website is not a substitute for in-person veterinary care. Always seek advice from your veterinarian if you have concerns about your pet’s medical condition.”

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