If you’ve ever been ambushed by a sudden wave of heat in a meeting, in bed, out of nowhere you’ve met the most common symptom of menopause. Here’s what’s actually happening, and why.

What they are

Vasomotor symptoms (VMS) also called hot flashes, hot flushes, night sweats, or temperature dysregulation are mini “heat waves” most commonly experienced during the menopause transition. They affect around 75–80% of women, which makes them the most common symptom of menopause. A hot flash is usually felt as a sudden wave of heat in the upper body, especially the face, neck, and chest. It may last one to five minutes, and can come with flushing, sweating, anxiety, palpitations, or even chills (sometimes called “cold flashes”). Frequency varies widely some women have a few a week, others many a day.

Night sweats are simply hot flashes that happen during sleep, often leading to waking, sweating, and difficulty falling back to sleep.

Why they happen

Although the mechanism is not fully understood, declining and fluctuating estrogen levels disrupt the hypothalamus the brain’s temperature regulator making it overly sensitive to small changes in body temperature. That oversensitivity triggers peripheral blood vessel dilation (the flushing), sweating, and sometimes chills, as the body tries to restore balance. Women with severe VMS appear to be especially sensitive to small temperature shifts.

Recent research points to overactive KNDy neurons in the hypothalamus with estrogen withdrawal or fluctuation, which send excessive neurokinin B signals that drive hot flashes and night sweats. That discovery has led to a new class of non-hormonal treatments that block this pathway relieving symptoms without the use of hormones.

This isn’t “all in your head” it’s your brain’s thermostat reacting to shifting estrogen.

How long they last

Hot flashes often begin in perimenopause and continue for an average of seven to eight years and for some women, more than a decade. About 25% of women experience moderate to severe hot flashes, the kind that can genuinely disrupt daily life.

Who tends to have them worse

The natural decline of ovarian hormone production is the primary cause. Surgical menopause (removal of the ovaries), or treatments like chemotherapy or radiation, can bring on sudden and more severe symptoms because the hormonal change is so abrupt. Smoking, obesity, and in some studies certain ethnicity (such as Black or Hispanic) are associated with higher risk and more severe symptoms, while some evidence suggests East Asian populations report fewer. Early menopause, whether natural or induced, can also mean more prolonged and severe symptoms.

The part worth taking seriously

Beyond the discomfort and sleep disruption, long-term studies suggest that frequent, persistent VMS may be linked to a higher risk of cardiovascular disease over time, and they can contribute to mood difficulties. That’s part of why managing them matters for more than comfort alone.

What makes them worse and better

Common triggers include heat and hot rooms, spicy food, alcohol, caffeine, stress, smoking, and excess weight. What tends to help: cool environments, dressing in layers, paced breathing, relaxation, healthy sleep hygiene, weight management, quitting smoking, and steering around your known triggers.

If your hot flashes or night sweats are disrupting your sleep, mood, or day, there’s a great deal that can be done which is the subject of our companion guide on easing them.

This article is general information, not medical advice. Any decision about managing menopause symptoms should be made with your own healthcare provider.