Up to 80% of women experience hot flashes during the menopause transition, yet most are never told what’s actually going on. The short version: a hot flash is your brain’s thermostat misfiring.
The thermoneutral zone
Your hypothalamus — a small region at the base of the brain — keeps your core temperature inside a comfortable band called the thermoneutral zone. Stray slightly above it and you sweat; slightly below it and you shiver.
Estrogen helps keep that band wide. As estrogen levels fall and fluctuate during perimenopause, the band narrows. Now a rise in core temperature that your body would once have ignored crosses the line, and the hypothalamus launches a full cooling response.
What the cooling response feels like
Within seconds, blood vessels near the skin widen to dump heat. That’s the sudden wave of warmth, usually across the chest, neck and face, often with visible flushing. Sweating follows. Heart rate can rise. Because the body overshoots, many women feel chilled afterwards.
A typical hot flash lasts one to five minutes. At night, the same event is called a night sweat — and it often wakes you, because sleep is lighter in the second half of the night.
Why it starts in the brain
Researchers have identified a group of neurons in the hypothalamus, known as KNDy neurons, that become overactive when estrogen drops. They release a signaling molecule called neurokinin B, which pushes the thermostat toward that hair-trigger state. This discovery is why a newer class of non-hormonal drugs works by blocking the neurokinin-3 receptor — targeting the switch itself rather than the symptoms.
What this means for you
- Triggers make sense now. Anything that nudges core temperature up — hot drinks, alcohol, spicy food, a warm room, stress — can tip a narrowed thermostat over the edge.
- Cooling strategies work at the margins. Layers, a cooler bedroom and breathable fabrics give you more room before you cross the threshold.
- Duration varies widely. In the long-running SWAN study, hot flashes lasted a median of around 7 years, and longer for women whose symptoms started early.
If hot flashes are disrupting your sleep, work or wellbeing, they’re worth raising with a clinician. Effective options exist — hormonal and non-hormonal — and the right one depends on your health history and preferences.