VOA慢速英语-SCIENCE IN THE NEWS - How to Protect Yourself Agains（在线收听）

People cool off in a swimming pool in Yongin, South Korea

Extremely hot weather is common in many parts of the world. Although hot weather just makes most people feel hot, it can cause serious medical problems -- even death.

Floods, storms and other natural events kill thousands of people every year. So does extreme heat. Experts say heat may be nature's deadliest killer.

For example, extreme heat was blamed for killing more than one hundred people in India and Pakistan in two thousand seven. Daytime temperatures rose to more than forty-five degrees Celsius in some areas. On June eleventh, the temperature in one desert town hit fifty-one degrees.

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Experts say the total heat of a hot day or several days can affect health. Several hot days are considered a heat wave. Experts say heat waves often become dangerous when the nighttime temperature does not drop much from the highest daytime temperature. This causes great stress on the human body.

Doctors say people can do many things to protect themselves from the dangers of extreme heat. Stay out of the sun, if possible. Drink lots of cool water. Wear light colored clothing made of natural materials. Make sure the clothing is loose, permitting freedom of movement. And learn the danger signs of the medical problems that are linked to heat.

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The most common health problem linked to hot weather is heat stress. Usually, it is also the least severe. The causes of heat stress include wearing heavy clothing, physical work or exercise, hot weather or high humidity. Humidity is the amount of water in the air.

If several of these conditions are present at the same time, a person's body temperature may rise above safe limits. The person loses large amounts of body water and salt in perspiration. Perspiration is one of the body's defenses against heat. It is how the body releases water to cool the skin.

Most people suffer only muscle pain as a result of heat stress. The pain is a warning that the body is becoming too hot. Doctors say those suffering muscle pain should stop all activity and rest in a cool place. They should also drink cool liquids. Do not return to physical activity for a few hours because more serious conditions could develop.

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Doctors say some people face an increased danger from heat stress. Such persons have a weak or damaged heart, high blood pressure, or other problems of the blood system. Severe heat increases problems for small children, older adults and those who have the disease diabetes.

It is also dangerous for people who weigh too much and have too much body fat, and for people who drink alcohol. Hot weather also increases dangers for people who must take medicine for high blood pressure, poor blood flow, nervousness or depression.

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A worker in Nashville, Tennessee, drinks ice water to fight the heat

Untreated heat stress can lead to a more serious problem called heat exhaustion. A person suffering from heat exhaustion loses too much water through perspiration. The person becomes dehydrated.

Dehydration limits a person's ability to work and think. Experts say a reduction of only four or five percent in body water leads to a drop of twenty to thirty percent in work ability. The loss of salt through perspiration also reduces the amount of work that muscles can do.

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A person suffering heat exhaustion feels weak and extremely tired. He or she may have trouble walking normally. Heat exhaustion may also produce a feeling of sickness, a fast heartbeat, breathing problems and pain in the head, chest or stomach. Doctors say people suffering from such problems should rest quietly in a cool place and drink plenty of water. They also say it may help to wash with cool water.

Heat exhaustion can develop quickly. But it also can develop slowly, over a period of days. Doctors call this dehydration exhaustion. Each day, the body loses only a little more water than is taken in. The person may not even know this problem is developing. But if the problem continues for several days, the effects will be the same as the usual kind of heat exhaustion.

Experts say that even a two percent drop in the body's water supply can cause signs of dehydration, including problems with memory and even simple mathematics.

The treatment for dehydration exhaustion is the same as for heat exhaustion. Drink plenty of water and rest in a cool place. Even better, doctors say, drink about two liters of water a day so problems with dehydration will not have a chance to develop.

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Heat exhaustion can lead to heat stroke if it is not treated. Heat stroke is the most serious disorder linked to hot weather. It results when the body is not able to control its temperature. The body's temperature increases and perspiration fails.

Generally, the body temperature rises to more than forty degrees Celsius. The body stops perspiring. The skin becomes dry and very hot. A person may become unconscious, not knowing what is happening.

Doctors say the body's tissues and organs begin to cook when its temperature is higher than forty-two degrees Celsius. Permanent brain damage and death may result. Immediate medical help is needed for someone with heat stroke. Doctors say such treatment is necessary or the person could die before help arrives.

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Children stay cool in a fountain near the Kremlin in Moscow last month

The purpose of immediate treatment is to cool the victim as quickly as possible to stop the body temperature from increasing. Begin by moving the victim out of the sun. Raise the person's feet up about thirty centimeters. Take off the victim's clothing. Put cool water on the body. Place pieces of ice in areas where blood passageways are close to the skin. These include the back of the neck and under the arms.

Experts say it is important to know the danger signs of the medical disorders linked to hot weather. It is also important to know what to do if the signs appear -- in yourself or in someone else.

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Experts say water is important for many health reasons. The body itself is between fifty-five and seventy-five percent water. Water in blood carries hormones and antibodies through the body. Water in urine carries away waste materials. Water is also needed for cooling the body on hot days, and when we are working or exercising. Water carries body heat to the surface of the skin. There, the heat is lost through perspiration.

Health experts say adults should drink about two liters of water a day to replace all the water lost in liquid wastes and perspiration. They say people should drink more than that in hot weather.

Experts say it is especially important to drink before, during and after exercise. They say we should drink water even before we start to feel like we need something to drink. This is because we sometimes do not feel thirsty until we already have lost a lot of body liquid.

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In hot weather, drinking cool liquids is best. Cool drinks do more than just replace lost body water. They also help cool us faster than warm liquids do. This is because they take up more heat inside the body and carry it away faster.

Yet experts advise against drinking sweet liquids in hot weather. The sugar they contain slows the liquid from getting into the blood system. Tea and coffee also are not effective. Doctors also warn against alcoholic drinks. Alcohol speeds the loss of body water through liquid wastes.

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Doctors say actions other than drinking water can protect against the heath dangers of heat. Stay out of the sun, if possible. Wear loose, light-weight and light colored clothes. Wear a hat or other head covering when in the sun. Eat fewer hot and heavy foods. If possible, cook foods during cooler times of the day. Also, rest more often. Physical activity produces body heat.

Experts say these simple steps can prevent the dangerous health problems linked to heat. They will prevent sickness, help you feel better and may one day even save your life.

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This SCIENCE IN THE NEWS program was written by Nancy Steinbach. Our producer was Brianna Blake. I'm Barbara Klein.

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And I'm Steve Ember. You can read and listen to this program on our Web site, voaspecialenglish.com. Join us again next week for more news about science in Special English on the Voice of America.