What causes hot flushes, and why they are worse at night

It arrives without warning. Heat climbs your chest and neck, your face goes red, and within a minute you are damp and looking for air. Then it passes, and you are cold.

Most explanations stop at “hormones”. That is true and not much use. Here is what is actually happening.

A hot flush starts in your brain, not your skin

Deep in your brain sits the hypothalamus. Among other jobs, it is your thermostat. It has a narrow band of temperature it is happy with, and it works hard to keep you inside it.

Oestrogen helps keep that band wide. As oestrogen falls, the band narrows. Your thermostat becomes touchy. A small rise in body temperature that you would not have noticed at forty now reads as overheating, and the brain responds the way it responds to real overheating: get rid of heat, immediately.

That response is the flush. Blood vessels near the surface of your skin widen so heat can escape, which is why you go red and feel hot. Then you sweat, because evaporation cools you. The whole sequence usually runs for a few minutes.

The chill afterwards is part of the same mechanism. Your body has just dumped more heat than it needed to, so for a while you are genuinely too cold.

Flushes usually begin during perimenopause, while periods are still happening, which surprises women who expect them only after periods stop. If you are unsure which stage you are in, the three stages are set out here.

Why the night version feels worse

A night sweat is the same event. What makes it worse is context.

Your body temperature naturally dips as you fall asleep and rises again towards morning, so the thermostat is already moving. You are under a duvet, which traps the heat you are trying to lose. And you are asleep, so you cannot do the small things you would do awake: push a sleeve up, move away from the window, take a sip of water. By the time your body has resorted to sweating hard enough to work, you are awake and the sheets are wet.

Then there is the second cost. Getting back to sleep after being woken hot is difficult, and a broken night makes the next day harder in ways that have nothing to do with temperature. Night sweats are only one of three reasons sleep breaks in these years, and they need different answers, which is covered in why menopause disrupts your sleep.

What makes a flush more likely

Triggers do not cause hot flushes. The narrowed temperature band causes them. But triggers nudge your temperature up, which is enough to set one off when the band is already narrow. Commonly reported ones:

• Hot drinks, spicy food and alcohol.
• Warm rooms, hot showers, heavy bedding.
• Caffeine, for some women.
• Stress and sudden anxiety.
• Smoking.

Worth knowing: your own triggers are not necessarily anybody else’s. A fortnight of noting what you had and what happened will tell you more than a general list. Some women find nothing they do makes much difference, and that is a real answer too, not a failure to look properly.

How long do hot flushes go on for?

Longer than most women are told. They often begin in perimenopause, before periods stop, and for many women they continue for several years past the final period. Some women have very few. Some have them for a decade. There is no way to know in advance which you will be, and starting late does not mean finishing late.

What is worth raising with your doctor

Hot flushes themselves are not dangerous. They are uncomfortable, and being uncomfortable for years is reason enough to ask about options; you do not need to justify it with anything worse.

Alongside whatever you discuss there, MenoLuv is our daily hormone-free soy drink for these years, and soy isoflavones are the most studied plant compound in this area if you want to read what the research measured.

Bring it up sooner rather than later if they are wrecking your sleep, if they started before you were 45, if they arrive with heavy or irregular bleeding, or if they come with symptoms that do not fit the pattern here, such as a racing heart, weight loss or fever. Those last ones can point somewhere other than menopause, and that is worth ruling out.