What Is a Hot Flush? The Science No One Explains

You are in the middle of a meeting and the heat arrives from nowhere. It climbs up your chest and neck, your face goes red, and within seconds your blouse is damp at the back. Thirty seconds ago you were fine. Now you are fanning yourself with a notepad and hoping nobody is looking. A hot flush is one of the most recognised signs of menopause, and also one of the most misunderstood. You have probably been told it is just part of getting older and that you should ride it out. What almost nobody explains is what is actually happening inside your body when one hits, and why it has nothing to do with weakness, stress, or you overreacting.

What a hot flush actually feels like

A hot flush is a sudden wave of heat that spreads through the upper body, often with skin flushing, sweating, and sometimes a racing heart. For many women it is followed by a chill as the body cools back down. Each episode usually lasts between thirty seconds and five minutes, but it can feel much longer when you are sitting through it.

What surprises many women is that before the heat itself, there is often a brief sense that something is about to happen — a prickle at the scalp, a wave of dread or agitation for no reason, a feeling of being suddenly switched on. Researchers call this the premonitory aura, and it can begin around thirty to sixty seconds before any heat is felt (Carpenter et al. 2018). Your heart rate has already started to climb before your brain registers the word hot.

Knowing this matters in a very practical way. The warning gives you a small window, and there are tools that work best if you use them in those first seconds rather than once the flush is in full swing.

What is happening in your brain during a hot flush

For years, hot flushes were explained as simply oestrogen dropping. The science now tells a more detailed story. Deep in your brain sits the hypothalamus, an area like a thermostat that controls body temperature. Inside it is a small cluster of nerve cells known as KNDy neurons. The name comes from three chemical signals they use: kisspeptin, neurokinin B, and dynorphin. While your oestrogen levels were steady, these neurons stayed quiet and balanced. As oestrogen falls and fluctuates through perimenopause, they become overactive.

One of the signals they release, neurokinin B, floods the brain's temperature centre and sends a false message: you are too hot. Your body believes it completely. It does exactly what it would do on a genuinely hot day. It opens the blood vessels near your skin, raises your heart rate, and switches on your sweat glands to shed heat that was never really there. The trigger is astonishingly small. A rise in core body temperature of as little as 0.03 to 0.05 of a degree Celsius — a few hundredths of a degree — can be enough to set the whole response in motion (Freedman 1999).

Here is the science:  A hot flush is not your body failing. It is your body responding correctly to a faulty signal. The heat is real, the sweat is real, and the response is exactly what your brain is designed to do — it has simply been triggered by a false alarm in the temperature centre (Khan et al. 2023).

Why the thermostat becomes so sensitive

There is a second element that explains why even small things set a flush off. Oestrogen normally widens what scientists call the thermoneutral zone — the comfortable temperature range your brain tolerates before it reacts. With steady oestrogen, that zone is wide enough that a warm room or a cup of tea passes without incident.

As oestrogen falls, that comfortable zone narrows, and in some women the gap between the temperature that triggers sweating and the temperature that triggers shivering can shrink almost to nothing (Freedman 1999). When the zone is that narrow, the smallest input tips you over the edge — a warm doona, a glass of wine still being broken down, a stuffy office. A rise of a few hundredths of a degree is all it takes, and your body reads it as overheating and launches the full cooling response.

This matters because it shifts the explanation away from you. You are not failing to cope with ordinary warmth — your thermostat has become so finely tuned that a change too small to notice produces a full-body response.

How common are hot flushes, and are you imagining the frequency?

Hot flushes and night sweats are grouped together under the medical term vasomotor symptoms, which simply means symptoms involving the widening and narrowing of blood vessels. Around 80 per cent of women experience them, and about one in four find them frequent or severe enough to affect their quality of life (Patel et al. 2025).

How often they come varies enormously between women. Researchers describe symptoms as high in frequency when they occur on six or more days in a fortnight (Patel et al. 2025). That variation is normal. It reflects how reactive your individual thermostat has become, not how well you are managing.

What this means for you

Understanding the mechanism changes how you respond to a flush in the moment. When you feel the early warning, try to act before the heat peaks rather than waiting until you are mid-flush.

Three slow breaths, with a longer breath out than in, help to settle the nervous system that is driving the response. Cooling the palms of your hands or the inside of your wrists with a cold glass shifts your sense of temperature faster than fanning your neck, because those surfaces exchange heat efficiently. None of this fixes the underlying hormonal change, but it makes each episode easier to manage while you decide on the bigger picture.

Most importantly, knowing that a hot flush is a real physiological event gives you the language to take it seriously and to ask for help, rather than quietly enduring it.

Three takeaways

1. A hot flush is a real event driven by overactive KNDy neurons in your brain's temperature centre — not stress, not weakness, and not you overreacting.

2. There is often a thirty to sixty second warning before the heat. Use that window for slow breathing and palm or wrist cooling.

3. Around 80 per cent of women experience hot flushes, and about one in four find them frequent or severe enough to affect their quality of life. The range is wide and normal.

This is not your body failing you. It is your body responding correctly to a faulty signal — and that signal can be addressed.

This information is educational only and does not constitute personal medical advice. Always consult a qualified health professional about your individual circumstances. © Menopause Hub 2026.

REFERENCES

Patel AH, et al. Advent of NK3R Antagonists for the Treatment of Menopausal Hot Flushes: A Narrative Review. BJOG 2025. doi:10.1111/1471-0528.18338. (Prevalence ~80%; ~25% problematic symptoms; high frequency defined as six or more days of episodes per fortnight.)

Carpenter JS, et al. What's in a name: are menopausal hot flashes a manifestation of neurovascular dysregulation? Menopause 2018;25(7):832–838. (Premonitory aura.)

Freedman RR, Krell W. Reduced thermoregulatory null zone in postmenopausal women with hot flashes. American Journal of Obstetrics & Gynecology 1999;181(1):66–70. (Core temperature trigger ~0.03–0.05°C within a reduced thermoneutral zone.)

Khan SJ, Kapoor E, Faubion SS, Kling JM. Vasomotor Symptoms During Menopause: A Practical Guide on Current Treatments and Future Perspectives. International Journal of Women's Health 2023. (Mechanism and false-alarm framing.)