Updated September 25, 2026. Fact-checked against veterinary sources; review by a licensed veterinarian is in progress. See our editorial policy.
Quick answer: Most female dogs that haven’t been spayed come into heat about every 6 months, though small breeds may cycle more often and giant breeds only once a year. A heat usually lasts 2–3 weeks, with a swollen vulva, bloody discharge, and a period when she’ll accept males. There’s no safe medication vets routinely use to stop a heat. Management means hygiene, comfort, and strict separation from intact males. Spaying prevents heats and serious uterine infection (pyometra).
Stages of the heat cycle
- Proestrus (about 9 days, can vary): swollen vulva and bloody discharge. Males are attracted, but she won’t accept them yet.
- Estrus (about 9 days, can vary): discharge often becomes lighter and straw-colored. She’s fertile and may seek out males.
- Diestrus (about 2 months): hormone levels stay high whether or not she’s pregnant. False pregnancy can occur during or after this stage.
- Anestrus: a resting phase until the next cycle.
First heats usually start between 6 and 15 months, later in large breeds.
Signs your dog is in heat
- Swollen vulva
- Bloody or straw-colored discharge, and more licking of the area
- Urinating more often, or marking
- Restlessness, clinginess, or grumpiness
- Tail held to the side when touched near the tail (a sign of estrus)
- Male dogs showing lots of interest
Managing her heat at home
- Keep her away from intact males for the whole cycle and a few days after. Males can smell a female in heat from a long way away and may jump fences.
- Leash walks only, even in a fenced yard, and avoid dog parks and daycare.
- Dog diapers or heat pants help keep your home clean. Change them often to prevent skin irritation and infection, and remove them for bathroom breaks.
- Washable bedding and covers on furniture.
- Keep her clean: wipe with a damp cloth or unscented pet wipes.
- Extra calm and attention: puzzle toys and quiet time help restless dogs.
Spaying
- Spaying ends heats and prevents unplanned litters and pyometra. Spaying before the first or second heat also greatly lowers the risk of mammary cancer.
- The best age to spay varies by breed and size. For some large breeds, research suggests waiting may reduce certain joint and cancer risks. Talk it through with your vet.
- Many vets prefer to spay 2–3 months after a heat, when the uterus has less blood supply, but it can be done during a heat if needed.
Warning signs after a heat
Pyometra is a life-threatening uterine infection that most often develops within about 2 months after a heat, usually in middle-aged or older unspayed dogs. See a vet immediately if your dog:
- Is lethargic or not eating
- Drinks and urinates much more than usual
- Has a smelly, pus-like, or bloody discharge, or a swollen belly
- Vomits or has a fever
With a “closed” pyometra there may be no discharge at all, so general illness after a heat always needs a vet.
Also call your vet if bleeding lasts more than about 3 weeks, heats come much closer together than usual, or she has signs of false pregnancy that don’t settle.
What to avoid
- Human pain relievers for discomfort. Ibuprofen, naproxen, and acetaminophen are dangerous for dogs.
- Products or supplements claiming to “stop” or “mask” a heat. Hormone drugs that suppress heat can cause serious side effects and aren’t routinely recommended for pet dogs.
- “Let her have one litter first”: there’s no health benefit to a litter before spaying.
- Diapers left on too long, which trap moisture and bacteria.
Frequently asked questions
Can my dog get pregnant on her first heat?
Yes. She can conceive on any heat, including the first.
Do dogs have periods like people?
Not exactly. The bleeding in dogs happens before ovulation, as part of heat, rather than as the shedding of the uterine lining.
My dog was accidentally mated. What should I do?
Call your vet as soon as possible to discuss options. Don’t use human medications.
Sources
- Merck Veterinary Manual: Reproductive physiology and the estrous cycle of dogs
- Merck Veterinary Manual: Pyometra in small animals
- American Veterinary Medical Association (AVMA): Spaying and neutering
- Hart BL, et al. Assisting decision-making on age of neutering for 35 breeds of dogs. Front Vet Sci. 2020
This article is for general education and is not a substitute for care from your own veterinarian. Learn about The Pet Vet and our editorial policy.