Signs Your Dog Is Going Into Heat

The earliest signs a dog is going into heat are usually a swelling vulva, spots of bloody or pink discharge, more frequent urination, extra licking of her rear, and clingy or restless behavior — often paired with sudden, intense interest from any intact male nearby. These signs mark the start of proestrus, the opening phase of heat. Not every dog shows all of them, and tidy self-groomers can make a heat look almost invisible, so it pays to know the full range.

Spotting the start of heat matters because the fertile window follows within days. If there's any chance of a mating, dates start counting immediately — and the free dog pregnancy calculator can turn a mating date into a due-date window in seconds. Below: the physical signs, the behavior changes, when to expect the first heat, and what's normal versus a vet call.

The Physical Signs to Watch For

The most reliable early tells are physical, and they cluster at the start of proestrus:

A swollen vulva. This is often the clearest sign. The vulva enlarges, sometimes noticeably, sometimes just enough that you'd only spot it if you were looking. Swelling tends to appear right at the start of heat, before or alongside any discharge.

Bloody or pink discharge. The classic sign most people picture. Early discharge is often bright to deep red and heaviest in the first several days, then lightens toward pink or straw-colored as the cycle moves into the fertile window. The amount varies enormously between dogs — big enough to need diapers in some, barely visible in others.

More frequent urination. A dog going into heat often pees more often and in small amounts, partly to spread scent signals. You might notice more marking behavior on walks.

Increased licking. Many dogs groom their rear far more than usual once heat begins — sometimes so thoroughly that they clean up discharge before you ever see it. Persistent licking of the genital area can be the first thing an owner notices, especially in tidy dogs.

The Behavior Changes

Heat isn't just physical. Hormones shift behavior, sometimes before the physical signs are obvious:

• Clinginess or neediness. Some dogs become velcro dogs, following you room to room and seeking extra affection.
• Restlessness or moodiness. Others get edgy, pace, whine, or seem generally out of sorts.
• Changes in appetite. Eating a little less (or occasionally more) is common and usually nothing to worry about on its own.
• More interest from male dogs. This is frequently the loudest signal of all. Intact males can detect a female entering heat from a surprising distance and will suddenly fixate on her — sometimes before you've noticed a single physical sign. If neighborhood dogs start showing up at your fence, take the hint.

Early in heat she'll typically refuse male attention even as they pursue it — the receptive, fertile stage comes a bit later. That mismatch (interested males, uninterested female) is itself a useful early marker. The full behavior picture is covered in dog in heat behavior explained.

When to Expect the First Heat

If you're watching a puppy for her first-ever heat, timing depends heavily on size:

First heats are also frequently irregular — lighter than later cycles, "silent" (minimal visible signs), or oddly spaced. An unremarkable or easily-missed first heat is normal. If a dog reaches around two years old with no sign of a heat at all, that's worth mentioning to your vet. More detail lives in what age do dogs go into heat.

How the Signs Progress

The early signs aren't a fixed snapshot — they evolve over the cycle. Reading the progression helps you tell "just starting" from "fertile now":

• Days 1–3ish (early proestrus): swelling begins, first spotting appears, males take notice, she refuses them.
• Mid proestrus: discharge often heaviest, behavior changes more obvious.
• Into estrus: discharge lightens in color and volume, swelling softens, and — crucially — she becomes receptive. This is the fertile window.

Here's the trap worth flagging: many owners relax when the bleeding lightens, assuming heat is winding down. Often it's the opposite — lighter discharge can signal the start of the fertile window, when pregnancy risk peaks. Watch behavior, not just blood. The full timeline is in how long does a dog stay in heat.

What to Do Once You Spot the Signs

The moment you're fairly sure heat has started:

1. Mark day one on a calendar. This is the anchor for tracking her cycle and predicting the next one (see how often do dogs go into heat).
2. Tighten containment. Leash-only outings, no dog parks, no off-leash areas, and a hard look at your fence and gate latches. Assume she'll try to get out and intact males will try to get in.
3. Manage the mess. Washable blankets over her favorite spots and washable dog diapers for indoor bleeding, if needed.
4. Watch her comfort. Some dogs sail through; others are visibly off. Quiet routines and patience help. Never give any human or leftover medication for discomfort.

If there's any chance a mating has already happened, note the date and, for an unwanted mating, call your vet promptly — options are time-sensitive.

Signs That Are Easy to Miss

Not every heat announces itself. A few situations make the signs subtle, so it's worth knowing where the misses happen:

• Tidy self-groomers. Some dogs clean up discharge so thoroughly you'll never see a drop. Swelling, extra licking, and male attention may be your only clues.
• Silent heats. Especially on a first cycle, a young dog can have a real heat with minimal visible signs. If you only watch for blood, you'll miss it — watch behavior and swelling too.
• Behavior-first heats. Some dogs show mood changes (clinginess, restlessness) a bit before obvious physical signs, so an out-of-character few days can be the earliest hint.
• Light first cycles. First heats are often lighter and shorter than later ones, making them easy to overlook.

The fix is to watch the whole picture — swelling, discharge, licking, urination, mood, and male interest — rather than waiting for one dramatic sign.

Tracking From Day One

The moment you spot the signs, that's day one of a cycle worth logging. A simple record pays off:

• Day one: first swelling or spotting.
• When discharge lightens: the fertile window likely opening.
• When everything returns to normal: heat over.
• The gap to the next heat: her personal interval.

After two or three cycles you'll know her pattern — how her heat looks, how long it runs, and roughly when to expect the next one. That makes spotting the next start almost effortless and helps you plan supervision, boarding, and grooming around it. See how often do dogs go into heat for what those intervals usually look like.

Normal vs. Call-the-Vet

Normal signs of going into heat: swelling, moderate bloody discharge that lightens over time, extra urination and licking, clingy or restless behavior, mild appetite changes, and lots of male attention.

Worth a vet call:

• Foul-smelling, green, or pus-like discharge — at any point, but especially in the weeks after a heat, when pyometra (a serious womb infection) classically appears. Combined with lethargy, heavy drinking, vomiting, or a swollen belly, treat it as urgent.
• Signs of genuine illness during the supposed heat — refusing food entirely, lethargy beyond mild moodiness, or apparent pain.
• Very heavy or very prolonged bleeding, or bleeding lasting well past four weeks.
• No first heat by around two years old.
• Heat-like signs in a spayed dog — worth ruling out retained ovarian tissue.

FAQ

What are the first signs a dog is going into heat?

Usually a swelling vulva and spots of bloody discharge, along with more frequent urination, extra licking, and clingy or restless behavior. Sudden interest from intact male dogs is often the first thing an owner notices, sometimes before the physical signs are obvious.

How long before a dog's heat do symptoms start?

The signs essentially mark the start of heat itself — proestrus is the first phase. There isn't a separate "pre-heat" period; when you see swelling and spotting, the cycle has begun. From there, the fertile window follows within roughly a week.

Can a dog go into heat without bleeding?

Yes. Some dogs have "silent" heats with minimal visible discharge, and fastidious groomers clean themselves up before you notice. Swelling, behavior changes, and male attention can be the only clues, which is why watching the whole picture beats watching only for blood.

How do I know if my dog is starting her first heat?

Watch for the same signs — swelling, spotting, licking, clinginess, male interest — around the age typical for her size, from about 6 months in small breeds to up to 24 months in giants. First heats are often light or irregular, so they can be easy to miss.

My dog is acting clingy but I see no discharge. Is she in heat?

Maybe. Behavior changes can precede or overshadow physical signs, and some dogs bleed very little. Check for vulvar swelling and watch for male attention. If you're unsure, note the date and keep watching — and see your vet if anything seems off rather than typical.

Should I do anything special when I spot the signs?

Mark day one, tighten containment (leash-only, no dog parks, secure fencing), and manage any mess with washable bedding or diapers. If a mating might have happened, note the date and call your vet promptly for an unwanted one.

Catch It Early, Plan Ahead

The signs your dog is going into heat — swelling, spotting, extra licking and peeing, mood shifts, and a crowd of interested males — all cluster at the start of the cycle. Spot them, mark day one, and tighten containment before the fertile window opens. Track a couple of cycles and you'll recognize her personal pattern instantly. And if a mating happens inside that window, get ahead of the next 63 days: the free dog pregnancy calculator turns the date into a due-date window and week-by-week plan in seconds.