Hot flashes are caused by changes in the brain’s internal thermostat, almost always triggered by shifting hormone levels. About 85% of women going through menopause experience them, and they affect men undergoing certain medical treatments as well. While menopause is the most common cause, several other conditions and medications can set them off.
How Your Brain’s Thermostat Goes Wrong
Your brain maintains body temperature within a narrow comfort zone. When your core temperature drifts above or below that zone, your body kicks in cooling or heating responses: sweating, flushing, or shivering. Estrogen plays a direct role in keeping this comfort zone wide enough that small temperature shifts don’t trigger a response.
When estrogen levels drop, a group of specialized nerve cells in the brain becomes overactive. These neurons essentially tighten the thermostat’s comfort zone so much that a tiny rise in core temperature, one your body would normally ignore, gets treated as an emergency. The brain responds by rapidly dilating blood vessels near the skin and triggering sweating to dump heat. That sudden rush of blood to the surface is what you feel as a hot flash: a wave of warmth across the chest, neck, and face, often followed by chills as your body overcorrects.
Heart rate also increases during an episode. Researchers have found this involves shifts in the autonomic nervous system, the same system that controls your fight-or-flight response. This is why hot flashes can feel surprisingly intense, sometimes mimicking anxiety or a pounding heart, not just warmth.
Menopause and Perimenopause
The most common cause of hot flashes is the natural decline in estrogen that happens around menopause. Roughly 55% of women start experiencing them during perimenopause, when periods become irregular but haven’t stopped. The frequency climbs sharply in the two years before the final menstrual period and peaks about one year after it.
Hot flashes are not a brief inconvenience for most women. A large meta-analysis found that the median duration of symptoms among affected women is about four years. Nearly half of all women still report hot flashes four years after their last period, and about 10% continue to experience them 12 years later. Symptom levels don’t fully return to premenopausal baseline until roughly eight years after menopause.
Severity varies widely. Some women notice a mild flush a few times a week. Others experience dozens of episodes per day, including night sweats that disrupt sleep. Factors like body weight, smoking history, and stress levels all influence how frequently and intensely hot flashes occur.
Hot Flashes in Men
Men can get hot flashes too, and the mechanism is the same: a drop in sex hormones narrows the brain’s thermoregulatory zone. In men, the hormone involved is testosterone. The most common scenario is androgen deprivation therapy for prostate cancer, which deliberately lowers testosterone to slow the growth of cancer cells. Between 70% and 80% of men on this treatment experience hot flashes, and they describe them in terms nearly identical to menopausal women: sudden heat, flushing, sweating, followed by chills.
Any condition that significantly lowers testosterone can produce the same effect, though prostate cancer treatment is by far the most frequent cause in men.
Medications That Cause Hot Flashes
Several widely prescribed drugs cause hot flashes as a side effect, particularly those that interfere with hormone activity. Tamoxifen, used for breast cancer treatment and prevention, is the most notable. Up to 80% of women taking tamoxifen report hot flashes, and about 30% of those rate them as severe. Related drugs like raloxifene and aromatase inhibitors cause fewer and less intense episodes, but the incidence still rises significantly compared to women not on these medications.
Opioid pain medications, certain antidepressants, and some blood pressure drugs can also trigger or worsen hot flashes. If you started a new medication and noticed hot flashes for the first time, the drug is a likely contributor.
Thyroid and Other Medical Conditions
Not all hot flashes trace back to sex hormones. An overactive thyroid gland (hyperthyroidism) speeds up metabolism across the body, causing heat sensitivity, sweating, and warm skin that can feel very similar to hormonal hot flashes. Graves’ disease, the most common cause of hyperthyroidism, is an autoimmune condition in which the immune system pushes the thyroid into overdrive. Overactive thyroid nodules and thyroid inflammation can produce the same effect.
If hot flashes come with unexplained weight loss, a rapid or irregular heartbeat, hand tremors, or visible swelling at the base of the neck, a thyroid problem is worth investigating. A simple blood test can confirm or rule it out.
Other, less common medical causes include certain tumors that release hormones or hormone-like substances, infections, and some neurological conditions. These are rare, but they’re worth considering if hot flashes appear without an obvious hormonal explanation.
Everyday Triggers That Set Off Episodes
Even when the underlying cause is hormonal, specific triggers can make individual episodes more frequent or intense. Common ones include:
- Alcohol and caffeine: Both affect blood vessel tone and can lower the threshold for a flash.
- Spicy foods: Capsaicin activates the same heat-sensing pathways your brain is already overreacting to.
- Hot beverages: Coffee, tea, or hot chocolate can raise core temperature just enough to trip the thermostat.
- Warm environments: Hot weather, heavy clothing, hot showers, or heated rooms.
- Stress: Emotional stress activates the sympathetic nervous system, which overlaps with the same pathways involved in flushing.
- Smoking: Smokers tend to experience more frequent and more severe hot flashes than nonsmokers.
Tracking which triggers affect you can make a real difference. Many women find that cutting one or two of these, especially alcohol and hot drinks before bed, noticeably reduces nighttime episodes.
Why Some People Get Them Worse Than Others
The speed of hormone decline matters more than the absolute level. A gradual decrease in estrogen or testosterone gives the brain’s thermostat more time to recalibrate. A sudden drop, from surgical removal of the ovaries or from starting hormone-blocking medication, tends to produce more severe and abrupt symptoms.
Body composition also plays a role. Higher body fat can intensify hot flashes during the menopausal transition, likely because fat tissue affects how hormones are metabolized and how efficiently the body releases heat. Physical activity, sleep quality, and baseline anxiety levels all feed into the system as well, since the brain’s temperature center doesn’t operate in isolation from the rest of the nervous system.
Race and ethnicity influence prevalence too. Large studies have consistently found that Black women report more frequent and longer-lasting hot flashes than white, Hispanic, or Asian women, though the reasons are not fully understood and likely involve a mix of biological, socioeconomic, and lifestyle factors.