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The San Diego Union-Tribune

Questions answered

November 22, 2007

QUESTION: I asked my physician if the temperature of a hot flash could be measured and what it might be, and he said he did not know. I have tried with my home thermometer, and it always reads normal, but it doesn't feel normal! Can you measure the temperature of a hot flash, and if so, how? Where in the body does the signal for a hot flash originate?

– Terry Burke, Lakeside

ANSWER: Hot flashes seem to be triggered by an overly sensitive body thermostat. A useful analogy is a house thermostat that is adjusted so that a temperature increase of a fraction of a degree switches on the air conditioning. A “false alarm,” such as heat wafting from opening the oven door, could activate the air conditioning, but since the house was not overly warm to begin with, the AC would rapidly turn off.

When the body's thermostat, which is located in the hypothalamus of the brain, decides it is too hot, it cranks on our bodies' air conditioning – sweating and dilation of blood vessels in the skin. It is the rush of warm blood to the skin that creates the feeling of intense heat characteristic of the hot flash.

If the ambient temperature is not actually high, our air conditioning quickly shuts down. The blood vessels in the skin constrict, and the blood drains away, leaving the skin pale and cold.

Studies have shown that, on average, women who experience hot flashes have lower core body temperatures and a lower sweating threshold – that is, they begin sweating at lower body temperatures – than women who do not experience hot flashes. However, the temperature difference is small, just a fraction of a degree, and therefore requires a very sensitive thermometer to measure.

The standard explanation for the occurrence of hot flashes during menopause is that they are triggered by declining levels of estrogen. Estrogen has been shown to ameliorate hot flashes by increasing the sweating threshold. However, it is not understood how declining estrogen levels could increase the sensitivity of the nerve cells in the brain that control body temperature.

Although considered the hallmark of the menopausal transition, hot flashes can occur at other times of life and can affect both women and men. Research is ongoing to determine if other hormones are involved, and to identify health and lifestyle factors that might increase a woman's chances of having hot flashes.


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