What Causes Hot Flashes: Your Brain's Thermostat

What is happening in the body during a hot flash?

A hot flash is a burst of heat-dissipating activity, flushing and sweating, set off by the brain rather than by the outside temperature. During an episode, blood vessels near the skin dilate, skin temperature climbs, and sweat glands switch on, all to shed heat quickly. Core body temperature barely moves, which is why a thermometer usually reads normal.

According to the World Health Organization, these vasomotor symptoms, hot flashes and night sweats, are among the most common features of the menopause transition 1Ref 1World Health Organization (2024).Menopause (fact sheet).Hot flashes and night sweats are among the most common vasomotor symptoms of the menopause transition, which for most women occurs between ages 45 and 55.. The sensation is real and sometimes intense, but it reflects a signaling change in temperature control rather than a fever or an infection.

Why does falling estrogen trigger hot flashes?

Estrogen helps tune the brain's temperature comfort zone, and when estrogen falls during menopause, that zone narrows. With a narrower comfortable range, a small rise in body heat that once went unnoticed now crosses the threshold and triggers a full cooling response. That is why a warm room, a hot drink, or a slight exertion can set off a flash.

The timing fits the hormonal shift. Estrogen becomes erratic in perimenopause and then stays low after the final period, which for most women occurs between the ages of 45 and 55 1Ref 1World Health Organization (2024).Menopause (fact sheet).Hot flashes and night sweats are among the most common vasomotor symptoms of the menopause transition, which for most women occurs between ages 45 and 55.. Reviewing broader menopause symptoms and what age perimenopause starts shows how vasomotor symptoms fit the wider transition.

What are KNDy neurons and the brain's thermostat?

KNDy neurons are a cluster of cells in the hypothalamus that help control both reproductive hormones and body temperature. They are named for the signaling molecules they use, including neurokinin B. As estrogen falls, these neurons enlarge and become more active, and researchers think their heightened signaling narrows the thermoneutral zone that keeps you comfortable.

Strong support for this model comes from treatment research. According to phase 3 trials, a non-hormonal medicine that blocks the neurokinin-3 receptor on these neurons reduced the frequency of moderate-to-severe hot flashes 2Ref 2Lederman S, Ottery FD, Cano A, et al. (2023).Fezolinetant for treatment of moderate-to-severe vasomotor symptoms associated with menopause (SKYLIGHT 1): a phase 3 randomised controlled study.A non-hormonal medicine that blocks the neurokinin-3 receptor on KNDy neurons reduced moderate-to-severe hot flashes in a phase 3 trial, supporting the KNDy-thermostat mechanism., which fits the idea that KNDy signaling drives the thermostat change. The finding links the mechanism directly to a target that, when quieted, eases symptoms.

How long do hot flashes last and how common are they?

Hot flashes affect a large majority of women during the menopause transition, and they can persist for years. According to the Study of Women's Health Across the Nation, vasomotor symptoms last a median of 7.4 years, and for some women more than 10 years 3Ref 3Avis NE, Crawford SL, Greendale G, et al. / Study of Women's Health Across the Nation (SWAN) (2015).Duration of menopausal vasomotor symptoms over the menopause transition.Vasomotor symptoms last a median of 7.4 years and more than a decade for some women, even though each individual hot flash is brief.. Each individual flash, though, is brief, usually peaking quickly and easing within 1 to 5 minutes, and how long menopause symptoms last varies widely from woman to woman.

The same thermostat mechanism explains hot flashes across life stages. Surgery that removes both ovaries can trigger sudden, often intense flashes because estrogen drops abruptly, and early menopause can bring them years ahead of the usual timing. Even the estrogen dip after childbirth can cause temporary flushes, showing that the trigger is the hormone change itself, not a particular age.

When hot-flash treatment options need a clinician

A clinician can explain which treatments target this thermostat and match them to your health history. According to The Menopause Society, options include hormone therapy, several non-hormonal medicines, and behavioral approaches such as cognitive behavioral therapy 4Ref 4The North American Menopause Society (Menopause Society) (2023).The 2023 nonhormone therapy position statement of The North American Menopause Society.Options for hot flashes include hormone therapy, several non-hormonal medicines, and behavioral approaches such as cognitive behavioral therapy.. For a deeper look at one common option, hormone therapy for menopause reviews the benefits and risks, while the right fit depends on symptom severity and your health history. Gale can help you outline your questions before that conversation.