Hot and cold flashes are sudden, intense shifts in your perceived body temperature. A hot flash brings a wave of heat, flushing, and sweating, often followed by chills as your body overcorrects and cools down rapidly. Between 60% and 80% of women experience these episodes during the transition to menopause, but hormonal changes from pregnancy, medications, and other medical conditions can trigger them too.
What Happens in Your Body During a Flash
Your brain has an internal thermostat, a small region called the hypothalamus that keeps your core temperature within a comfortable range. Normally, that range is fairly wide, so minor temperature fluctuations don’t trigger a response. During a hot flash, that comfort zone narrows dramatically. A tiny rise in core temperature that your body would normally ignore instead trips the alarm, launching a full heat-dumping response: blood vessels near the skin dilate, your heart rate increases, and you start sweating.
The “cold flash” that often follows is a direct consequence. After your body rapidly sheds heat through sweating and flushed skin, your core temperature can dip below that narrowed comfort zone, triggering shivering and chills. Some people experience the cold phase without a noticeable hot phase first, which can be confusing, but the underlying mechanism is the same destabilized thermostat.
A single episode typically lasts 1 to 5 minutes, though the residual chills or discomfort can linger longer. They can strike during the day or at night, where they’re commonly called night sweats.
Why Estrogen Loss Triggers the Thermostat Problem
The most common cause of hot and cold flashes is falling estrogen levels. When estrogen drops, a cluster of specialized nerve cells in the brain’s arcuate nucleus becomes hyperactive. These cells normally help regulate reproductive hormones, but they also send direct signals to the thermoregulatory area of the hypothalamus. Without estrogen to keep them in check, they enlarge and start producing more of a signaling molecule called neurokinin B.
Neurokinin B sensitizes the neurons that control your heat-loss response, essentially lowering the trigger point so that even a slight warm signal from your skin or core sets off a full flush-and-sweat episode. At the same time, increased levels of norepinephrine, a stress-related chemical messenger, further compress the thermoneutral zone from the other direction. The result is a thermostat so hair-trigger that your body ping-pongs between overheating and overcooling responses throughout the day.
Menopause Is the Most Common Cause
Hot and cold flashes are the hallmark symptom of perimenopause and menopause. They often begin in the years leading up to a woman’s final menstrual period, when estrogen levels start fluctuating unpredictably. On average, people who experience hot flashes have them for more than seven years, and some deal with them for over a decade. Frequency varies widely: some women have a few episodes a week, others have dozens a day.
Night sweats can be particularly disruptive. Waking up drenched in sweat, then shivering as the moisture cools, fragments sleep and contributes to the fatigue, irritability, and concentration problems many women report during this phase of life.
Other Causes Beyond Menopause
Any condition that disrupts estrogen or destabilizes the hypothalamus can produce hot and cold flashes. After childbirth, estrogen and progesterone levels plummet rapidly, and the hypothalamus reacts as though the body is overheating. These postpartum episodes are especially common in women who are breastfeeding, because prolactin (the hormone that drives milk production) keeps estrogen suppressed for longer.
Surgical removal of the ovaries causes an abrupt, rather than gradual, drop in estrogen, which often produces more severe flashes than natural menopause. Certain cancer treatments that suppress estrogen, including some breast cancer therapies, are another well-known trigger. Thyroid disorders, anxiety disorders, and infections can also cause temperature instability that mimics classic vasomotor symptoms, though the mechanism differs.
Common Triggers That Make Episodes Worse
Even when the underlying cause is hormonal, specific triggers can increase the frequency or intensity of individual episodes. The most consistently reported ones include:
- Warm environments and hot beverages: Anything that nudges core temperature upward can tip a narrowed thermoneutral zone into a full flash.
- Spicy foods: Capsaicin activates heat receptors in the mouth and gut, sending warming signals to the hypothalamus.
- Stress and anxiety: Emotional arousal increases norepinephrine, which further compresses the thermoneutral zone.
- Caffeine: Acts as a mild stimulant that can raise heart rate and core temperature.
- Smoking: Associated with earlier onset and more severe hot flashes, likely through its effects on estrogen metabolism.
The relationship between alcohol and hot flashes is surprisingly unclear. Some research shows current alcohol use is associated with fewer hot flashes in perimenopausal women, while other studies in postmenopausal women suggest the opposite. The mechanism behind either finding isn’t well understood, and hormone levels don’t appear to explain the difference.
How Hot and Cold Flashes Are Treated
For mild symptoms, lifestyle adjustments can make a real difference. Dressing in layers, keeping your bedroom cool, using moisture-wicking fabrics for sleep, and identifying your personal triggers are practical first steps. Regular physical activity and maintaining a healthy weight are linked to less frequent episodes, though they won’t eliminate flashes entirely.
Hormone therapy remains the most effective treatment for moderate to severe hot flashes. Replacing the estrogen your body is no longer producing directly addresses the root cause by calming the overactive nerve cells that destabilize the thermostat. It’s not appropriate for everyone, particularly women with a history of certain cancers or blood clots, so the decision involves weighing individual risks and benefits.
For women who can’t or prefer not to use hormones, a newer option targets the problem at a different point in the chain. In 2023, the FDA approved fezolinetant, a medication that blocks the neurokinin 3 receptor, the exact receptor through which those hyperactive brain cells sensitize the thermostat. By intercepting that signal, it reduces flashes without replacing estrogen. Certain antidepressants that affect norepinephrine and serotonin levels also provide partial relief, which is why they’ve been prescribed off-label for hot flashes for years.
Hot Flashes vs. Cold Flashes
People sometimes search for “cold flashes” as though they’re a separate condition, but they’re two sides of the same coin. The hot phase is your body aggressively trying to dump heat. The cold phase is the overcorrection, sometimes accompanied by genuine shivering, goosebumps, and a deep internal chill. Not every episode includes both phases. Some people primarily experience the sweating and flushing, while others notice the chills more. The balance can shift over time or vary by time of day.
If you’re experiencing cold flashes without any preceding warmth or sweating, and you’re not in a life stage where hormonal shifts are expected, it’s worth investigating other causes like thyroid dysfunction or blood sugar irregularities, both of which can produce sudden chills and temperature instability.