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The Science Behind What Happens In a Woman's Body During a Hot Flash

By HERWriter
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science behind hot flash Lev Dolgachov/PhotoSpin

Despite the bold and assertive name by which the hot flash is known, her origins remain elusive. Of course, doctors and scientists understand many of the mechanisms of menopause such as the reduction in estrogen and the important relationship between the ovaries and the pituitary gland, but the central cause of hot flashes – the heating of a woman’s core – is a secret Mother Menopause has yet to reveal.

“I’ve written editorials that we’ve sent men to the moon and we’ve broken the genetic code, but we cannot really explain the physiology of a hot flash,” said Cynthia Stuenkel, M.D., clinical professor of medicine, endocrinology and metabolism at the University of California, San Diego, School of Medicine in La Jolla, Cal.

What is known then? The hot flash seems to be an equal-opportunity phenomenon, plaguing as many as 75 percent of women, regardless of race or reproductive history. Whether you had children, and how many, and at what age, or remained childless, doesn’t seem to have any correlation with hot flashes, their severity or frequency. Nor does breastfeeding history or the age at which a woman began or stopped menstruating.

Smoking is believed to bring on menopause about one to two years early and some inherited tendencies can mean that women in the same family may see their eggs becoming less responsive around the same time of life. Obesity is believed to cause more hot flashes in some medical circles. But other doctors disagree.

What they do agree upon is that the thermoregulatory center of the brain which regulates temperature somehow loses its typical functioning capacity as estrogen decreases. Follicle-stimulating hormone (FSH) is produced by the pituitary gland in the brain. Its job is to stimulate the dominant follicle on one of a woman’s ovaries each month to release an egg.

But as the number of eggs decline throughout a woman’s childbearing years, the ovaries makes less estrogen and communicate this situation to the pituitary by “talking back” to it with a hormone called inhibin. The pituitary responds to the decline in estrogen by sending out more FSH, a hormone that is often measured when trying to gauge a woman’s fertility.

What isn’t more intimately understood is how the declining estrogen levels affect thermoregulation in the brain and specifically a center called the hypothalamus. Internal and external symptoms do not mirror the subtleties going on in the brain.

During a typical hot flash, which lasts from two to five minutes, a woman experiences a feeling of heat, usually in the upper torso, as blood vessels dilate. “In some women that are fair you’ll see some redness,” said James Liu, M.D., chair of the department of obstetrics and gynecology at University Hospitals/MacDonald Women’s Hospital at Case Western Reserve University School of Medicine in Cleveland, Ohio and a member of the Board of Trustees of the North American Menopause Society.

Liu said the internal core temperature actually drops a little despite the feeling of heat, while fingertip temperature goes up. Epinephrine, also known as adrenaline, courses through the bloodstream, sometimes causing an increased heart rate.

That can be disconcerting to women who have been taught of late not to ignore what can be the more subtle symptoms of heart attack in women. Liu offers simple advice for determining the difference between a hot-flash-induced pounding heart and a heart attack. “A heart attack is unrelenting,” he explains. “A heart attack episode is constant.”

The pounding heart that comes with the hot flash ends with the heat. Unfortunately, that drop in core temperature often sends women on a rollercoaster ride in the other direction, now feeling cold, and, of course, often very wet from copious sweating.

“We don’t know what triggers the temperature instability. That’s something we’re trying to figure out,” Liu said, echoing Stuenkel, and explaining that normally humans maintain a very stable temperature even under warm conditions.


Cynthia Stuenkel, M.D. via phone interview July 3, 2015 James Liu, M.D., via phone interview July 6, 2015

Reviewed July 8, 2015
By Michele Blacksberg RN

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We value and respect our HERWriters' experiences, but everyone is different. Many of our writers are speaking from personal experience, and what's worked for them may not work for you. Their articles are not a substitute for medical advice, although we hope you can gain knowledge from their insight.


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