Whether this is your dog's fifth heat or you're just not sure what you're looking at, here's the full list of signs — physical and behavioral — along with the ones that can look like heat but actually mean something else entirely.
Physical Signs
- Swollen vulva — often the earliest and most reliable sign, appearing a few days before bleeding starts
- Vaginal discharge — typically bright red at first, gradually lightening to pink or straw-colored as the cycle progresses
- Drops of blood left behind when she sits or lies down, rather than blood appearing in her urine stream
- Nipple changes — slight enlargement is common, though usually more subtle than what's seen in pregnancy
- Increased urination frequency, partly due to hormones and partly because she's scent-marking more than usual
Behavioral Signs
- Flagging — holding her tail to the side or up and away when touched near the rear, a receptivity signal
- Clinginess or restlessness, more than her usual temperament
- Mounting or humping — other dogs, toys, or even furniture; this is a normal hormonal behavior during heat, not a training failure or dominance issue
- Increased scent-marking, including in spots she doesn't normally mark
- Attracting male dogs, sometimes from well beyond your yard or block
- Mood swings — some dogs become more affectionate, others more irritable or snappish, particularly with other dogs
Why Does She Hump Other Dogs (or My Leg)?
Mounting behavior during heat is driven by hormones, not dominance or bad manners, and it can show up even in dogs who've never done it before or since. It usually fades once she moves past the fertile stage of her cycle. If it becomes disruptive, redirecting her attention with a toy or short training break works better than scolding — she's not being defiant, she's responding to a hormonal surge she doesn't have much control over.
Wait — Could This Be Something Else? Heat vs. UTI vs. Incontinence
Bleeding and frequent urination show up in all three of these, which is exactly why they get confused. Here's how to tell them apart:
| Sign | Heat | UTI | Incontinence |
|---|---|---|---|
| Where the blood comes from | Vagina — drops left behind when sitting, not mixed into urine | Bladder — blood is visibly in the urine stream itself | Not typically bloody |
| Vulva appearance | Visibly swollen | Usually normal | Usually normal |
| Urination pattern | Slightly more frequent | Frequent, small amounts, often straining or crying | Leaking, especially while relaxed or asleep, without squatting to go |
| Odor | Mild, not foul | Often noticeably foul-smelling | Usually not foul |
| When to call the vet | Only if bleeding is excessive, lasts unusually long, or is foul-smelling | Promptly — UTIs need treatment and rarely resolve on their own | Soon — often manageable but worth diagnosing the cause |
For more detail on the other two, see our guides to female dog UTI symptoms and treatment and female dog incontinence.
Yes, Male Dogs Really Can Smell Her From Far Away
A female dog in heat releases pheromones that intact male dogs can detect at a genuinely surprising distance — commonly cited estimates run into multiple miles under favorable wind and weather conditions, thanks to a dog's exceptionally sensitive sense of smell and a specialized scent-detecting structure called the Jacobson's organ. The practical takeaway matters more than the exact number: don't rely on a fence or a normally-reliable dog's recall during this period. Keep her leashed on walks and supervised in the yard, since a determined intact male may show up from well outside your property.
When a Sign Means Something Other Than Normal Heat
Most heat cycles are unremarkable. A few things are worth a vet call regardless of where she is in her cycle:
- Discharge that's green, yellow, or has a strong foul odor rather than blood-tinged
- Bleeding that continues well past three weeks
- Signs of pain, lethargy, or loss of appetite
- Any of these symptoms appearing two to eight weeks after a heat cycle has ended, rather than during it — this timing is a hallmark of pyometra, a uterine infection that's a genuine emergency. Our guide to pyometra covers exactly what to watch for.
Explore This Guide
- Female Dog Heat Cycle: The Complete Guide — the full overview
- How Long Do Dogs Stay in Heat? — the day-by-day timeline
- Her First Heat: What to Expect — for first-time owners
- Managing a Dog in Heat — practical mess and product tips
- Pyometra in Dogs — the emergency to know about
