6 Signs That Your Dog Is in Heat

A black and a white labrador playing in backyard

Stefan Cristian Cioata / Getty Images

If you're the loving owner of a female dog that has not been spayed, you definitely need to know the signs of your dog being in heat. A female dog of reproductive age that has not been spayed is called a bitch. Canine estrus, or heat, can occur at any time of year. A dog that is spayed cannot go into heat since her ovaries have been surgically removed, leaving the canine sterile.

Your Dog's First Heat

The age of a dog's first heat varies greatly. The average age for the first heat is 6 months, but small breeds may come into heat earlier. Large or giant breeds may experience their first heat as late as 18 to 24 months of age.

Signs That Your Dog Is in Heat

The more aware you are of your dog's cycle, the more prepared you will be for any physical changes and mess that may occur during the dog's estrus. These six signs are what to look out for: 

  • Swollen vulva: This non-painful swelling typically develops a few days before any discharge or bleeding will occur.
  • Bleeding: A bloody discharge from your dog's vulva may be the first sign of heat that you notice. Discharge consistency and color varies during the cycle. It can range from bloody to clear, brown, or straw-colored. The amount of discharge varies from slight to heavy, depending on the dog, as does the length of time discharge occurs.
  • Mounting behavior: Your dog may try to mount other dogs, objects, or your leg. During heat, she will probably tolerate being mounted by other dogs, which may be a change from her normal behavior.
  • Licking genital area: This is your dog's attempt at keeping the area clean. Depending on the dog, this may or may not be successful. Some dogs need to wear "doggy diapers" during the heat cycle to prevent soiling of bedding and the house.
  • Agitated or nervous behavior: Your dog might appear more anxious or clingy than usual while in heat.
  • Urinating more often: Frequent urination is a way of marking and letting other dogs know she is in heat. If you suspect urinary problems, which are also indicated by excessive licking of the genital area or frequent urination, it is important to take your dog to the veterinarian as soon as possible.
illustration of signs your dog is in heat
The Spruce / Vin Ganapathy

The 4 Stages of the Heat Cycle

There are four stages of the canine estrous (heat) cycle. Each has it's own characteristics and lasts for different amounts of time. 

  1. Proestrus: The most obvious signs during the first phase are vaginal swelling and bloody discharge. Males dogs will be attracted to female dogs but the females will be unwilling to mate. This phase usually lasts between 7 and 10 days, although some dogs will have shorter or longer proestrus.
  2. Estrus: The dog will have a swollen vulva. Vaginal discharge may change from red to yellow, brown, or clear. During estrus is when mating occurs. This second phase usually lasts between 7 and 10 days although some dogs will have a shorter or longer estrus.
  3. Diestrus: This is the time after estrus that typically lasts for around 60 days. 
  4. Anestrus: This is the period of sexual and hormonal inactivity between diestrus and the next proestrus. Anestrus can last anywhere between 90 and 150 days.

Specific timing will vary with each dog. Spaying is the best way to prevent pregnancy. Optimal timing for the surgery depends on a dog's individual circumstances, but it is often done before a dog's first estrus. The spay surgery removes both of the ovaries and often the uterus as well. It is a very common surgical procedure and can be done by a primary care veterinarian or at a spay/neuter clinic. If you have any questions about your dog's estrous cycle or see any worrisome behavior or symptoms, speak to your veterinarian right away. 

If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.