Hot flashes: why they happen, how long they last and what helps

Hot flashes happen because your brain reacts more sharply to small temperature shifts while your oestrogen falls. They almost always last longer than women expect. In the SWAN study, frequent hot flashes persisted for a median of 7.4 years.

That number changes the conversation. Not because it is bleak, but because it moves you from "just get through it" to having a plan.

What strikes us about the questions Lunara receives: women underestimate that duration, and overestimate what a single hormone test can say about it. More on both below.

What exactly is a hot flash?

A hot flash is a sudden wave of heat across your face, neck and chest. Sweating, flushed skin and sometimes palpitations come with it. It builds within seconds and usually fades within five minutes. Doctors call these vasomotor symptoms.

The explanation sits in your hypothalamus, the temperature centre of your brain. That centre works with a thermoneutral zone: a margin inside which your body does not need to act.

As oestrogen levels fall, that margin narrows. Freedman and Krell measured in 1999 that women with hot flashes had a clearly narrower zone than women without symptoms. A tiny rise in core temperature then already falls outside the margin.

Your body responds as if you are overheating. The blood vessels in your skin open wide, you start sweating, and afterwards you feel cold.

That last part is often forgotten.

It explains why you can shiver after a flash, and why a cool bedroom beats an extra blanket. Your thermostat is not broken. It is set more sensitively.

How many hot flashes a day is normal?

There is no medical cut-off for normal. Research usually works with bands, where roughly four or more in 24 hours counts as frequent. What matters in the consulting room is not the count, but how much it disrupts you.

The table below is descriptive, not diagnostic. Its main use is making your symptoms concrete before you see your GP.

Track it for two weeks before booking. Note the time, the duration and what you were doing.

Those two weeks are worth more than any self-test. They show a pattern you would never reconstruct from memory.

How long do hot flashes last?

Longer than most women think. In the SWAN study, which followed more than 1,400 women for years, frequent vasomotor symptoms lasted a median of 7.4 years. Among women whose final period was observed, they continued for a median of 4.5 years afterwards.

Median means half had less, and half had more. It is not a prediction for you personally.

There is a pattern worth knowing. Women whose symptoms started early in perimenopause had the longest total duration on average. Women whose symptoms started only after their final period were done fastest.

We think that is one of the most useful figures in menopause research. It takes the pressure off "when will this end" and moves it to "what do I want to do in the meantime".

The stage-by-stage picture is in the 5 phases of menopause.

Why do hot flashes hit in the evening and at night?

Your core temperature fluctuates across the day and peaks in the early evening. Because your thermoneutral zone is narrower, that normal peak now falls outside the margin more often. This is why hot flashes and night sweats cluster in the evening and the first hours of sleep.

Night sweats are the same reaction, except you sleep through it until it gets severe. Many women only wake once the bed is already damp.

The result is fragmented sleep rather than short sleep. You might be in bed for eight hours and wake five times.

A few things that make a practical difference: a bedroom around 17 degrees, cotton or linen instead of synthetics, and two thin duvets you can kick off separately. Alcohol close to bedtime backfires for many women.

How sleep and menopause reinforce each other is covered in poor sleep during menopause.

At what age do hot flashes usually start?

Most Dutch women get their first hot flashes between 45 and 55, in the years around their final period. The average age of menopause in the Netherlands is around 51. For many women hot flashes begin several years earlier, during perimenopause.

If they start consistently before 40, that is worth having checked. Not because it always means something, but because early menopause does have consequences for your bones and heart.

More on that in early menopause symptoms and osteoporosis after menopause.

What helps against hot flashes without hormones?

No single remedy works for everyone. What research and practice suggest helps most is a combination of avoiding triggers, keeping your environment cool and protecting your sleep. RIVM and Thuisarts also point to physical activity and not smoking as general measures.

The best-known triggers are hot drinks, spicy food, alcohol, smoking and a warm room. Stress belongs on the list too, though it is harder to steer.

The point of triggers is not that you should cut everything. The point is working out which of those five actually counts for you.

For most women that is one or two, not all five. It saves a lot of unnecessarily strict living.

On herbal preparations and phyto-oestrogens we are more cautious than most web shops. The evidence is mixed and the quality of over-the-counter products varies widely. Discuss them with your GP or pharmacist, certainly if you take other medication.

If nothing helps enough, hormone therapy is a reasonable conversation to have. What the options are is set out in menopause hormone therapy.

Which blood values change during menopause?

During menopause your oestradiol falls and your FSH rises, because your brain pushes harder at ovaries that respond less. That shift is real, but in perimenopause it is erratic. A single measurement therefore cannot confirm or rule out that you are in menopause.

This is what we run into most often. A woman has her hormones tested, gets a value labelled normal, and concludes her symptoms are not menopausal.

When two weeks later the number could have been entirely different.

So your FSH value and oestradiol value are context, not proof. In Dutch general practice, menopause is diagnosed on your symptom pattern and your cycle, not on a tube of blood.

Here is an example we use often. Two women aged 48 have their FSH measured. Both come back at 28 IU/l.

The first has had an erratic cycle for eight months. She sleeps badly and gets hot flashes daily. The second still menstruates like clockwork and notices nothing.

Same number, entirely different story.

For the first woman the value fits a clear picture. For the second it says almost nothing. A single measurement only captures the swing of that one week.

This is why we keep pushing the symptom pattern. The number plays the supporting role.

Where blood testing does add something is in ruling out other explanations. That is the next section.

For a value-by-value walkthrough, see hormone balance during menopause.

When are hot flashes not menopause?

Hot flashes are not exclusive to menopause. An overactive thyroid, anaemia, certain medications and anxiety can produce the same sensation. The distinction is worth making, because the approach differs per cause.

The table below is meant to sharpen your conversation with your GP. It does not make a diagnosis and does not replace an assessment.

If you have hot flashes without any change in your cycle, that first row is less likely. We worked through the other causes separately in hot flashes without menopause.

The thyroid trail is the one most often missed. Slow thyroid and menopause covers the reverse confusion.

To my mind that second row is the most important in the table. An overactive thyroid feels almost identical from the inside. The difference sits in what happens around it, not in the heat itself.

Which other symptoms belong to this?

Hot flashes get the most attention, but they rarely arrive alone. Dizziness, nausea, back pain and hair loss are often not linked to menopause by women themselves, even though they surface in the same period. Recognising that they belong together saves months of searching.

We described the four that go unrecognised most often:

• Dizziness during menopause, with the vestibular explanation and what to rule out.
• Hair loss during menopause, and why the pattern differs from iron deficiency.
• Nausea during menopause, a symptom that rarely makes the standard lists.
• Back pain during menopause, with what MRI research showed in more than 1,500 women.

And because alcohol keeps coming up with hot flashes: menopause and alcohol lays out the numbers.

When should you see your GP?

Go if your hot flashes structurally affect your sleep, work or mood, if they start before you are 40, or if you have symptoms alongside the heat that do not fit menopause. Any bleeding after menopause is always a reason to make contact.

Bring your two weeks of notes and your medication list. That turns a vague conversation into a concrete one.

What strikes me most: women wait too long, because they assume menopause is something to sit out. It is not. There is plenty to choose from, including if you would rather avoid hormones.

If you want to rule out the other explanations in the same appointment, the menopause check or the broader menopause blood test lets you include your thyroid and iron values. Discuss the result with your GP afterwards.

References

• Avis NE, Crawford SL, Greendale G, et al. Duration of menopausal vasomotor symptoms over the menopause transition. JAMA Internal Medicine, 2015. PMID 25686030.
• Freedman RR. Menopausal hot flashes: mechanisms, endocrinology, treatment. Journal of Steroid Biochemistry and Molecular Biology, 2014. PMID 24012626.
• Freedman RR, Krell W. Reduced thermoregulatory null zone in postmenopausal women with hot flashes. American Journal of Obstetrics and Gynecology, 1999. PMID 10411797.
• RIVM, information on health and lifestyle around menopause.
• Thuisarts.nl, menopause and hot flashes.

Lunara Health provides blood testing and explanation, not diagnosis. Your results are reviewed by a BIG-registered doctor. Always involve your GP if you have symptoms, and do not use this article to treat yourself or adjust medication.