Hot flashes: 6 proven causes, with or without menopause

Hot flashes affect nearly eight in ten postmenopausal women, but they do not always come from the ovaries. Prostate cancer treatment, an overactive thyroid, an antidepressant, alcohol or marked anxiety trigger the same wave of heat, in women as in men. Here are the six causes documented by research, the clues that tell them apart and the signs that call for a medical visit.

Hot flashes: definition and key figures

A hot flash shows up as sudden heat rising toward the chest, neck and face, followed by sweating and sometimes a chill. The heart speeds up and the skin turns red. At night, the same phenomenon is called night sweats. Doctors speak of vasomotor symptoms, because everything happens through the small blood vessels of the skin.

Their frequency depends first on hormonal stage. In a cohort of 436 women followed for six years in Philadelphia, 79% of postmenopausal women reported these episodes (Freeman et al., 2005). The proportion was 37% in women still having regular periods, 48% in the early transition and 63% in the late transition. In the SWAN study (3,198 American women), the likelihood of having them peaked in late perimenopause, 6.6 times higher than before the transition (Gold et al., 2006).

Their duration often comes as a surprise. In SWAN, frequent episodes (at least 6 days out of 14) lasted a median of 7.4 years in 1,449 women (Avis et al., 2015). They persisted 4.5 years after the final menstrual period, and 9.4 years when they had started early.

After 60, the symptom does not always go away. Among 2,020 Australian women, 6.5% of postmenopausal women aged 60 to 65 still had moderate to severe episodes (Gartoulla et al., 2015). The figure was 15.1% between 55 and 59, and 28.5% before 55.

Mechanism: why the brain’s thermostat goes haywire

Each hot flash starts in the hypothalamus, the brain region that regulates body temperature. Normally, the body tolerates small variations in core temperature: this is the thermoneutral zone, between the sweating threshold and the shivering threshold. In women with symptoms, this margin shrinks almost to zero.

• In 12 symptomatic postmenopausal women, this gap measured 0.0°C, compared with 0.4°C (about 0.7°F) in 8 women without symptoms (Freedman and Krell, 1999).
• A tiny rise in core temperature is then enough to set off an episode. During exercise in the laboratory, every symptomatic woman had a hot flash, and none of the others did.
• KNDy neurons in the hypothalamus (kisspeptin, neurokinin B, dynorphin) are held in check by estrogen. When estrogen falls, these neurons become active and stimulate the thermoregulatory center through the NK3 receptor (Rance et al., 2013).
• Greater activation of the sympathetic nervous system, through alpha-2 adrenergic receptors, narrows this thermoneutral zone even further (Freedman, 2014).
• The result: skin blood vessels dilate, sweating starts and the pulse speeds up to get rid of heat that was never in excess.

This circuit explains why very different causes produce the same sensation. A rapid drop in estrogen or testosterone throws it off balance, in women as in men (Spetz et al., 2003). In 37 women, blocking the NK3 receptor cut the number of weekly episodes by 45 percentage points (Prague et al., 2017). Other causes bypass the hormonal step and dilate the blood vessels directly.

What the science says: the 6 proven causes of hot flashes

Six causes rest on solid studies: two work through a drop in sex hormones, four through other pathways, in women as in men.

1. Menopause and perimenopause

Menopause remains by far the leading cause of hot flashes. They often appear as early as perimenopause, when periods become irregular and estrogen levels fluctuate, as the National Institute on Aging explains. In SWAN, late perimenopause weighed more than age, education level or weight. Early menopause produces the same symptoms. An estimated 1 to 2% of women have premature ovarian insufficiency, meaning the ovaries stop working before age 40.

2. A treatment-induced hormone drop: breast cancer, prostate cancer

Treatments that suppress sex hormones reproduce a more abrupt menopause. In women, removal of the ovaries, chemotherapy and estrogen-blocking hormone therapy are the main sources. After breast cancer, 65 to 85% of women suffer from hot flashes or night sweats (Mann et al., 2012).

In men, the best-documented cause is androgen deprivation, which drives testosterone down in prostate cancer. In a Scandinavian trial of 915 men, 74.3% of patients on complete androgen blockade had hot flashes (Spetz et al., 2001). Only 30.1% of those on injectable estrogen did. A systematic review highlights their impact on quality of life and the small number of well-evaluated treatments (Frisk, 2010). The data are thinner for the slow decline in testosterone with age, covered in our article on andropause.

3. Hyperthyroidism

An overactive thyroid speeds up metabolism and increases heat production, which can bring on heat surges at any age. Heat intolerance, sweating, palpitations, tremor and weight loss are the classic signs. After 60, these signs become subtle. Among 3,049 patients with hyperthyroidism, older patients had markedly fewer classic symptoms at equal severity, except for weight loss and shortness of breath (Boelaert et al., 2010). The authors argue for more systematic thyroid testing after 60, especially in people with atrial fibrillation. A TSH test, explained in our article on normal TSH after 60, is enough for an initial screen.

4. Medications and alcohol

Several medications trigger heat surges or sweating. Among 413 American primary care patients aged 65 to 94, 9.2% reported at least moderate night sweats. Three drug classes stood out (Mold and Holtzclaw, 2015):

• Selective serotonin reuptake inhibitor (SSRI) antidepressants tripled the risk of night sweats (odds ratio of 3.01).
• Sartans (angiotensin II receptor blockers), prescribed for high blood pressure, reached an odds ratio of 3.44.
• Thyroid hormone replacement came next (odds ratio of 2.53).

Tricyclic antidepressants, SSRIs and venlafaxine are among the known causes of excessive sweating, which often subsides after an adjustment agreed with the doctor (Marcy and Britton, 2005). The paradox: venlafaxine also reduces the vasomotor symptoms of menopause. High-dose niacin (vitamin B3) causes a flush by releasing prostaglandins in the skin, and the body gets used to it quickly (Kamanna et al., 2009).

The NHS suggests avoiding or cutting down on alcohol, spicy food, caffeine and hot drinks during menopause, although these tips have not been validated by high-quality studies. In about 36% of people of East Asian descent, a single drink causes intense facial redness, linked to a deficiency of the ALDH2 enzyme. This flush is not harmless: in these people, drinking markedly increases the risk of esophageal cancer (Brooks et al., 2009).

5. Anxiety and stress

Anxiety does more than accompany hot flashes: it comes before them. In the Philadelphia cohort, moderately anxious women reported them nearly three times as often, and the most anxious women nearly five times as often. This link held after taking into account menopausal stage, smoking, weight and estradiol. Anxiety measured at one visit predicted episodes at the next. In SWAN, anxiety symptoms at baseline tripled the likelihood of having them (odds ratio 3.10). Outside menopause, a panic attack often combines a feeling of heat, sweating and palpitations, which is why it is sometimes mistaken for a hot flash.

6. Secreting tumors, rare but not to be missed

A few rare diseases cause flushing episodes by releasing substances into the blood that dilate the blood vessels. For unexplained flushing, a dermatology review lists four serious diagnoses to rule out with tests: carcinoid syndrome, pheochromocytoma, mastocytosis and anaphylaxis (Izikson et al., 2006). Most facial redness, however, has benign causes, such as rosacea or menopause. Carcinoid syndrome combines flushing and diarrhea. It affected 19% of the 9,512 Americans aged 65 and over diagnosed with a neuroendocrine tumor between 2000 and 2011 (Halperin et al., 2017).

What makes hot flashes worse: smoking and excess weight

Two modifiable factors increase their frequency. In SWAN, smoking multiplies the likelihood of episodes by 1.63, and each point of body mass index adds 3%. The Australian study finds the same link, with an odds ratio of 1.6 for smoking and 1.7 for excess weight.

A signal to take seriously for the heart

In women, frequent and long-lasting vasomotor symptoms are more than a simple discomfort. In SWAN, among 3,083 women followed for 22 years, frequent episodes at baseline were associated with a 51% higher risk of cardiovascular events. The excess risk reached 77% when they persisted from one visit to the next (Thurston et al., 2021). The pooled analysis of six studies (23,365 women) links severity above all to risk (Zhu et al., 2020). In that analysis, severe episodes went hand in hand with a cardiovascular risk multiplied by 1.83. These are associations, not proof that the symptom damages the arteries. Above all, they are a reason to monitor blood pressure, cholesterol and blood sugar in the years after menopause.

In practice: identifying the cause of your hot flashes

The context is often enough to point to the cause. Age, sex, periods, current treatments and associated signs allow the doctor to decide in most cases. The table below sums up the clues that distinguish the six causes.

A diary kept for two weeks (time, intensity, context, meals, alcohol, medications) gives an objective picture of the symptom, over the same period as the one used in SWAN. For women, our guide to the levers for aging well after menopause details the impact of this transition on bones and the heart. These episodes reflect a disruption of hormonal signaling, one of the mechanisms of aging described in our pillar on altered intercellular communication.

Tips: what reduces hot flashes according to trials

Treating the cause comes first: correcting hyperthyroidism or adjusting a medication often makes the resulting episodes disappear. For episodes linked to menopause, only placebo-controlled trials can show whether an option works. In the Cochrane review, placebo alone already reduced their frequency by 57.7% (MacLennan et al., 2004).

The North American Menopause Society considers hormone therapy the most effective treatment. Its benefit-risk balance is favorable before age 60 or within 10 years of menopause, in the absence of contraindications. Beyond that, the risks of coronary heart disease, stroke, blood clots and dementia weigh more heavily (NAMS, 2022). The NHS sets out who can take these treatments and their benefits and risks. In France, fewer than 6% of postmenopausal women take them, according to Inserm.

Fezolinetant has been authorized in the European Union since December 7, 2023. After cases of liver injury, the European Medicines Agency requires liver tests before treatment, then every month for three months. For women who avoid hormones, the North American Menopause Society recommends cognitive behavioral therapy, clinical hypnosis, certain antidepressants, gabapentin and fezolinetant. It rules out paced breathing, herbal supplements, soy and exercise as treatments (NAMS, 2023).

In daily life, a few simple steps follow from these data:

• Record your episodes for two weeks, then bring this log to your appointment.
• Have your prescriptions reviewed if the episodes began after a new treatment, without ever stopping it on your own.
• Quit smoking, one of the best-established aggravating factors.
• If you are overweight, lose weight: each 5 kg (11 lb) lost increased the odds of improvement by 32%.
• Keep your bedroom cool for comfort, even though the effect on the frequency of episodes has not been demonstrated.

Some situations call for a medical visit without delay:

• Hot flashes in a man not on hormone therapy, or in a young woman with regular periods.
• Flushing with diarrhea, wheezing, severe headaches or blood pressure spikes.
• Night sweats with fever, unexplained weight loss or swollen lymph nodes.
• Episodes that keep you from sleeping or working.

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Frequently asked questions about hot flashes

Why do I have hot flashes when I am not in menopause?

Outside menopause, they most often come from an overactive thyroid, a medication (antidepressant, sartan, thyroid hormone, niacin), alcohol or marked anxiety. A treatment that shuts down hormones, such as breast cancer treatment, also causes them. Early perimenopause often goes unnoticed as long as periods continue. A TSH test and a review of your treatments are the first steps.

Can men have hot flashes?

Yes, men can have them too. The best-documented cause is hormone therapy for prostate cancer, which drives testosterone down. In a trial of 915 men, 74.3% of patients on complete androgen blockade had them. Hyperthyroidism, certain medications, alcohol and anxiety are other causes. In a man not on hormone therapy, repeated episodes warrant a medical visit.

How long do menopausal hot flashes last?

In the US SWAN study, which followed 1,449 affected women, frequent episodes lasted a median of 7.4 years, including 4.5 years after the final menstrual period. They last longer when they start early, before or at the start of perimenopause: more than 11.8 years on median. Between 60 and 65, 6.5% of women still have them in a moderate to severe form.

What is the difference between a hot flash and flushing?

A hot flash combines an intense feeling of heat, redness and sweating. It comes from a malfunction of the brain’s thermostat, as in menopause. Flushing refers to a sudden reddening of the skin, sometimes without sweating, caused by substances that dilate blood vessels: alcohol, niacin or, more rarely, a neuroendocrine tumor. Flushing without sweating along with diarrhea should prompt a medical visit.

Are hot flashes dangerous for the heart?

They are not dangerous in themselves, but they signal a risk. In the SWAN study, which followed 3,083 women for 22 years, frequent episodes at baseline were associated with 51% more cardiovascular events. This excess reached 77% when they persisted. This is an association, not a cause-and-effect relationship. It justifies monitoring blood pressure, cholesterol and blood sugar.

When should you see a doctor for hot flashes?

See a doctor when they disrupt sleep or daily life, or when they affect a man or a young woman with regular periods. See one too if they come with other signs: weight loss, palpitations, diarrhea, severe headaches, fever or heavy night sweats. These combinations point to an overactive thyroid, an infection or, rarely, a secreting tumor, all of which require tests.