Anatomy of a Hot Flash

Menopause symptoms: What goes on inside when the heat rises

A prickling sensation. Flushing cheeks. Rising heat that seems to break over your skin like waves. Quick, somebody open a window!

Yep, it's a hot flash—also known as a "hot flush," "night sweat" or, in medical terms, "vasomotor flushing." Hot flashes affect as many as 85 percent of women, sometimes disrupting sleep or everyday activities.

Scientists don't know the exact trip wire for this poster-girl symptom of the big M, but they have a pretty good idea of what one looks like from the inside. It starts (as so many things do) with an egg, or rather in this case, the lack of an egg. Women are born with millions of them, and the ovaries release them one at a time every month from puberty through perimenopause (the transitional years before menopause, or the last period). When relatively few eggs remain, fewer sex hormones are needed to prepare for a monthly egg drop and so estrogen and progesterone levels begin to fluctuate. This leads to a narrowing of the range of temperatures that the body considers to be normal. These hormonal changes are felt all through the body in various ways— most notoriously in a hot flash.

Here's how a typical hot flash plays out:

·Blood hormone levels suddenly shift.
·Temperature-control portions of the hypothalamus in the midbrain sense that the body is too hot (even when it isn't), and trigger the cool-down process.
·Skin temperature rises, blood vessels in the skin dilate and blood flow increases. A wave of heat spreads to the upper body and face, and skin may become flushed. The heat-and-sweat sensation can range from mild to quite severe.
·Sweat glands step up production to cool the body.
·After two to five minutes, skin temperature returns to normal and the hot flash is over, although a chill may follow as the damp body cools. Some women experience waves of flashes in close succession, which can feel like one long bout in a sweat lodge.

Some women experience an "aura," a sensation of uneasiness or dizziness (or even nausea and headache) anywhere from a few seconds to a few minutes before any heat is felt.

Who gets them: Any woman can, but some are more vulnerable. These include smokers, those with a higher than normal body mass index (BMI), non-exercisers and African Americans. Asian women are least likely to have hot flashes.

When they strike: Everybody has different triggers. Keeping a hot flash diary can help you discover patterns in what sets off yours. Common triggers: becoming overheated (in a hot room, wearing too many clothes or during exercise), drinking alcohol or caffeinated beverages and eating spicy foods. There's evidence that women who are anxious or depressed are more likely to have hot flashes.

Basic management: Keeping cool—literally and figuratively—helps beat the heat. Dress in layers and lower the thermostat. At night, sleep between 100 percent cotton sheets and keep a glass of water within easy reach. Try using relaxation techniques such as meditation, slow and deep breathing, tai chi or mindfulness-based stress reduction. Physical activities such as yoga and walking have been linked to a lower incidence of hot flashes in some women.

While hormonal therapy with estrogen and progesterone is the gold standard for treating hot flashes, some women cannot or prefer not to use it. Antidepressants that increase serotonin or both serotonin and norepinephrine (brain chemicals) are now being studied as another treatment option.

A quick fix: At the start of a hot flash, inhale deeply through your nose, hold the breath for a count of four, and exhale slowly through your mouth. Repeat a few times.

WATCH: What to Expect From the “Big M”

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