Hot flashes are caused by changes in the brain’s temperature control center, almost always triggered by declining levels of sex hormones. The most common cause is the drop in estrogen during menopause, but medications, medical conditions, and lifestyle factors can also set them off. About 80% of women experience hot flashes during the menopausal transition, and the median duration of moderate to severe episodes is 10.2 years.
How Your Brain’s Thermostat Goes Haywire
Your body maintains a comfortable core temperature by keeping it within a narrow range called the thermoneutral zone. Think of it as a thermostat’s comfort band: as long as your core temperature stays inside that range, your body doesn’t activate sweating or shivering. In women without hot flashes, that zone is about 0.4°C wide. In women with hot flashes, it shrinks to essentially zero. That means even a tiny rise in core temperature, one that would normally go unnoticed, crosses the upper threshold and triggers a full heat-dumping response: sweating, flushed skin, and a racing heart.
The narrowing of this zone traces back to a specific group of brain cells in the hypothalamus. These neurons produce three chemical signals: kisspeptin, neurokinin B, and dynorphin. Researchers call them KNDy neurons. Estrogen normally keeps these neurons quiet. When estrogen drops during menopause, the neurons lose that brake and start overproducing neurokinin B. The excess signaling floods the brain’s thermoregulatory center, making it hypersensitive to even minor temperature changes.
This is why estrogen withdrawal is so central to the story, but it’s not the whole story. Estrogen reduction alone doesn’t fully explain who gets hot flashes and who doesn’t. The brain chemical norepinephrine also plays a role. Higher levels of norepinephrine in the brain narrow the thermoneutral zone further. This helps explain why some women sail through menopause with few symptoms while others are severely affected: it depends on how multiple systems interact, not just one hormone level.
Menopause and Perimenopause
The most common trigger is the hormonal shift that begins in perimenopause, sometimes years before periods stop entirely. As estrogen levels fluctuate and then decline, KNDy neurons in the hypothalamus become increasingly active. The result is episodes of sudden warmth, typically starting in the chest and face, often accompanied by sweating and a visible flush. When these happen at night, they’re called night sweats.
Many women assume hot flashes are a brief inconvenience around the time of their last period. The data suggests otherwise. A large study tracking women over time found the median duration of moderate to severe hot flashes was 10.2 years. When milder episodes were included, the median stretched to 11.6 years. Some women experience them well into their 60s or beyond. Women who begin having hot flashes earlier in the menopausal transition tend to have them for longer.
Hot Flashes in Men
Men don’t experience menopause, and testosterone levels decline slowly, roughly 1% per year after age 40. Most men retain enough testosterone throughout their lives that hot flashes never become an issue. The major exception is men undergoing androgen deprivation therapy for prostate cancer, which dramatically lowers testosterone. Between 70% and 80% of these men develop hot flashes.
The mechanism is the same in principle: the hypothalamus loses the hormonal signal that keeps the thermostat stable, and the body starts overreacting to small temperature changes. Men on temporary androgen deprivation typically recover within three to four months of stopping treatment. For those on long-term therapy, the problem can persist. One study found over 40% of men still had hot flashes after more than eight years of treatment.
Medications That Cause Hot Flashes
Several classes of drugs can trigger hot flashes by interfering with hormone levels or brain chemistry. The most notable offender is tamoxifen, a breast cancer treatment that blocks estrogen’s effects on tissue. Up to 80% of women taking tamoxifen experience hot flashes. Other medications known to cause them include:
- Hormone-blocking cancer drugs, including raloxifene and injectable drugs that suppress sex hormone production
- Fertility medications like clomiphene, which alter estrogen signaling
- Certain antidepressants, including tricyclics, MAO inhibitors, and some serotonin-targeting drugs
- Some blood pressure medications, particularly calcium channel blockers
- Chemotherapy, which can damage the ovaries and trigger early menopause
If you’ve started a new medication and noticed hot flashes for the first time, the drug is a likely culprit. Stopping or switching medications often resolves the problem, though that decision depends on why the medication was prescribed in the first place.
Lifestyle and Dietary Triggers
Certain habits and body characteristics don’t cause the underlying dysfunction but can increase how often and how severely hot flashes strike. Being overweight is one of the strongest associations. Women with a BMI in the overweight range (25 to 29.9) were roughly three times more likely to have hot flashes compared to women at a healthy weight. Excess body fat acts as insulation and may also affect hormone metabolism in ways that amplify symptoms.
Smoking is another significant factor. Tobacco use was associated with about a threefold increase in the likelihood of experiencing multiple vasomotor symptoms. Poor cardiovascular fitness showed an even stronger link: women with low cardiorespiratory fitness were up to 16 times more likely to experience night sweats or palpitations compared to women who were more fit.
Diet matters too. Research has found that women who ate more red meat, white meat, seafood, and dairy reported more vasomotor symptoms, while women eating a primarily plant-based diet reported fewer. High intake of saturated fat from animal sources may worsen symptoms by affecting cholesterol and vascular function. Elevated fasting blood sugar, above 100 mg/dL, was also associated with more frequent symptoms, suggesting that metabolic health and hot flashes are closely connected.
Common situational triggers, things like a warm room, a hot drink, spicy food, or stress, don’t cause hot flashes in the biological sense. But when your thermoneutral zone is already razor-thin, any small bump in core temperature can push you over the threshold. That’s why these everyday exposures can set off an episode that wouldn’t have happened before menopause.
Other Medical Conditions
While menopause is by far the most common cause, hot flashes occasionally point to something else. Thyroid disorders, particularly an overactive thyroid, can produce similar flushing and heat sensations because excess thyroid hormone speeds up metabolism and raises body temperature. Certain cancers and cancer treatments can also cause hot flashes. These non-menopausal causes are rare, but they’re worth considering if you’re experiencing hot flashes at an unusual age or without an obvious hormonal explanation.
What’s Happening Inside Your Body During an Episode
A hot flash begins when your core temperature nudges above your narrowed sweating threshold. The hypothalamus interprets this as overheating and triggers a rapid cooldown: blood vessels near the skin dilate (especially in the face, neck, and chest), sweat glands activate, and heart rate increases. You feel a sudden wave of heat, your skin may visibly redden, and sweating can range from mild to drenching.
Here’s the irony: the cooling response works too well. After the flush, core temperature drops below the lower threshold of the thermoneutral zone, which can trigger chills or shivering. This is why many women describe a hot flash as a wave of heat followed by feeling cold and clammy. The whole cycle, from onset to resolution, typically lasts one to five minutes, though the lingering discomfort and sweat can make it feel much longer.
Why Understanding the Cause Matters for Treatment
For decades, the only effective treatment was estrogen therapy, which works by restoring the hormonal brake on those overactive KNDy neurons. It raises the sweating threshold back up, widening the thermoneutral zone so minor temperature fluctuations no longer trigger episodes. Estrogen remains the most effective option for most women, but it’s not appropriate for everyone, particularly women with a history of certain cancers.
The discovery of neurokinin B’s role opened a new path. A newer class of medication works by blocking the receptor that neurokinin B uses to overstimulate the brain’s thermostat. By dampening that specific signal at the KNDy neurons, these drugs reduce hot flashes without involving estrogen at all. This approach represents the first treatment designed around the actual brain circuitry that causes the problem, rather than broadly replacing hormones.
Lifestyle changes target the modifiable risk factors. Losing weight, improving cardiovascular fitness, quitting smoking, and shifting toward a more plant-based diet have all been associated with fewer and less severe episodes. These changes won’t fix the underlying neurobiology, but they can lower the baseline so that fewer everyday triggers push you past the threshold.