Dog in heat: when it starts, how long it lasts and what owners should do

2026-10-104 min read

A dog's first heat usually starts at 6–12 months: earlier in small breeds, and in large and giant breeds sometimes not until 18–24 months. Heat comes roughly every 6 months and lasts 2–3 weeks on average. Signs: a swollen vulva, bloody discharge, frequent urination, interest from male dogs and behaviour changes. During this time walk your dog only on a lead, away from males; at home, dog diapers and pads help. Pus-like discharge, lethargy and strong thirst after a heat are reasons to see a vet urgently.

Stages of the heat cycle

Stage	Duration	What happens
Proestrus	About 9 days on average	The vulva swells, bloody discharge, males are interested but the female won't accept them
Oestrus	About 9 days on average	Discharge becomes lighter, the female accepts males and moves her tail aside — ovulation occurs and pregnancy is possible
Dioestrus	About 2 months	Discharge stops; false pregnancy may develop
Anoestrus	Several months	A resting phase until the next heat

Stage length varies a lot between dogs, so you can't count “safe” days on a calendar: pregnancy is possible during almost the entire heat.

Signs that a heat has started

a swollen vulva;
bloody discharge — very slight in some dogs, especially those that lick themselves clean;
frequent stops and marking on walks;
extra attention from male dogs;
behaviour changes: clinginess or irritability, disobedience, restlessness, changes in appetite.

How to walk your dog during heat

On a lead only — even the most obedient dog may run off in heat. Use a reliable lead and check the collar or harness buckle.
Avoid dog parks and places where dogs run off-lead.
Walk at quiet times and on different routes.
Don't leave her alone in the garden: males can climb fences.
Warn other owners if an off-lead male approaches.

Keeping the home clean: diapers and pads

Dog diapers (season pants) protect furniture and carpets from discharge. Choose by waist size with a tail hole, such as CROCI Doggy Pants or hygiene pants No. 2 for a spaniel or French bulldog. You can add a replaceable pad inside. Take them off for walks and at night so the skin can breathe, and make sure your dog doesn't overheat.

Important: season pants are not contraception — a male can pull them off. Pads are handy on the bed and favourite spots, for example Trixie 40×60 cm. More in dog toilet accessories.

Warning signs: see a vet urgently

pus-like, foul-smelling discharge;
lethargy, refusing food, vomiting;
strong thirst and frequent urination, especially 2–8 weeks after a heat;
a swollen belly, fever;
a heat lasting much longer than 3–4 weeks or coming too often.

These symptoms may point to pyometra — a life-threatening infection of the uterus. In the closed form there may be no discharge at all.

False pregnancy after heat

1–2 months after a heat, some dogs develop a false pregnancy: the mammary glands swell, milk may appear, and the dog builds a nest, carries and guards toys, and becomes restless or lethargic. It usually passes on its own within 2–3 weeks. More walks and play to distract her and a temporarily smaller portion help. Don't express milk or massage the nipples — that stimulates lactation. Remove the toys she is mothering. If the glands are hot, painful or red, or she refuses food, see a vet: it could be mastitis.

Mating, heat-suppressing pills and spaying

Breeding a dog on her first heat isn't recommended: her body isn't ready yet. Don't use hormonal drugs to suppress heat without a vet's prescription — they raise the risk of pyometra and tumours. If you don't plan puppies, discuss spaying with your vet: it ends heats and lowers the risk of several diseases. After an unplanned mating, contact your vet straight away.