Dear Doctors: I had a scare exercising on a hot day. I got a terrible headache, my skin got clammy and I felt really weak. I was sure I was going to faint. I had to get into a cool bath to start feeling better. I drank plenty of water and was sweating a lot. Shouldn't that have protected me?
Dear Reader: You have described the symptoms of heat exhaustion. It's a heat-related illness on a spectrum that ranges from unpleasant to life-threatening. These illnesses occur when the body begins to exceed the fairly narrow span of core temperature of 97 to 99 degrees Fahrenheit that it needs to function properly.
When you begin to overheat, your body takes immediate steps to counteract it. The first is cooling the blood by sending it to the surface of the skin. It causes the reddened flush we get during exercise. This is accompanied by sweating, which provides surface moisture for an evaporative effect. When these are insufficient, core body temperature will begin to rise. That's when heat illness sets in.
Known as hyperthermia, heat illnesses are a serious health threat. On the milder side are heat cramps. These are painful muscle spasms that can occur during or after strenuous exercise in hot weather. While not an immediate threat to health, they can be a warning sign of heat exhaustion.
In heat exhaustion, core body temperature begins to rise. In addition to resting and gradually rehydrating, it's important to cool the skin to reverse the effects of excessive heat. This can be done with a bath or shower, or by spraying or sponging the skin with cool water.
If left untreated, heat exhaustion will progress to heat stroke. This is a medical emergency. Without immediate medical intervention, heat stroke can cause permanent disability, and potentially lead to death. Heat stroke occurs when the body loses all control over maintaining core temperature. The symptoms are similar to those of heat exhaustion. However, in heat stroke, the body stops producing sweat. Skin becomes dry, red and hot to the touch. Someone with heat stroke will also have a rapid and pounding pulse, confusion and eventually lose consciousness.
You're correct that drinking plenty of water, which the body needs to produce sweat, is crucial to preventing heat-related illnesses. However, sometimes it's not enough. In areas of high humidity, sweat evaporates far more slowly, if at all. This cancels out the body's primary cooling mechanism. Exercise is another factor. The action of our muscles generates a large amount of heat. When exercising in hot weather, it's possible to raise core body temperature to dangerous levels. This is known as exercise-induced hyperthermia.
To stay safe, exercise early in the day, when it's cooler. Spend the heat of the day in a cool place. If your home is inadequate in this regard, use public spaces, such as malls, public libraries and senior citizen centers, which are air-conditioned. Many communities open dedicated cooling centers during a heat wave. We have experienced extended heat waves all over the United States this summer. Please take the potential threat of these hot days seriously.
(Send your questions to [email protected], or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)
