They strike at the most inopportune times: During meetings, at dinner, in bed. The face flushes, the heart races. Fingers tingle and perspiration washes over the body. They're hot flashes, and for more than 70 percent of women, they're an inconvenient and sometimes unpleasant reality of menopause.
So what's the cause?
Carolyn Crandall, a professor of medicine at UCLA's David Geffen School of Medicine, has bad news: "We don't know the answer."
The symptoms seem to begin in the hypothalamus, the part of the brain that helps regulate body temperature. Hormonal changes may cause the hypothalamus to tell the body it's really hot. As a result, the body responds with such things as sweating and dilated blood vessels -- reactions that usually occur when the body is actually experiencing extreme heat.
But it's not really clear what triggers this process, how to stop it and even whether a lack of estrogen, the female sex hormone that declines in middle age, is its cause.
Women with a history of smoking, psychological conditions such as depression and anxiety, and high body mass indexes appear to be at higher risk, according to research. There's no telling how long any particular woman will experience hot flashes; on average, they last seven years -- even longer for African American women -- and they may persist for a lifetime.
Options for attempting to relieve hot-flash symptoms include traditional hormone replacement therapy, or HRT, and bioidentical hormone therapy, which mimics hormones produced by ovaries using plant or animal derivatives.
Self-management is another approach, for which the National Institute on Aging recommends dressing in layers, carrying a portable fan, maintaining a healthy weight and trying mindfulness techniques to ease discomfort.
HRT was common until about 15 years ago, when a major trial suggested it increased women's risk of heart disease and some breast cancers.
But for a woman who can't take the heat, there's no shame in compensating for the estrogen lost during menopause.
"She should not feel bad," says Crandall, who adds that a woman is the only one who can decide if her symptoms are distressing enough to warrant hormone therapy. "And if her doctor's not open to that discussion, she needs to find another one."
Not all bioidentical hormones are created equal.
The Food and Drug Administration has approved some bioidentical hormones such as estradiol, which is chemically identical to the estrogen produced by the ovaries.
However, compounded bioidentical hormones -- preparations that are custom-blended for a patient, often based on saliva and hormone tests that identify purported hormonal deficiencies -- are not FDA-approved. According to the agency, there is not enough credible evidence to support claims that they are safe or effective, and because they are mixed on a person-by-person basis in different doses and combinations, there's no way to effectively regulate them. Crandall recommends asking instead for FDA-approved hormones.
A recent study suggests that five to seven years of traditional hormone therapy may be safe -- for certain groups. The study found that women who take HRT for up to seven years had no greater mortality risk than women who did not. This jibes with a position statement by the North American Menopause Society that treatment should be individualized. Women younger than 60 who are within 10 years of the onset of menopause are more likely to benefit from traditional hormone therapy.
It's unclear whether HRT will come back into fashion. Most medical associations recommend that women who choose it take the lowest dose possible for the shortest time possible.
Learn more: womenshealth.gov/menopause.