From VOA Learning English, this is Science in the News.

　　I'm Anna Matteo.

　　And I'm Christopher Cruise.

　　Today we talk about hot weather, and the problems it can cause. We also tell you about the best ways to prevent and treat problems caused by extreme heat.

　　Heat Waves Can Be Deadly

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

　　Several hot days that follow each other are considered a heat wave. Experts say heat waves often become dangerous when the nighttime temperature does not drop much past the highest daytime temperature. This puts great pressure on the human body.

　　Extreme heat can be harmful to very young children -- especially when they are left in a car. Every year, there are news reports about young children dying after they were left inside cars in the summer sun.

　　Jan Null is a meteorologist -- a weather expert -- at San Francisco State University in California. Since 1998, he has recorded deaths of children from what medical experts call "vehicular heatstroke." He says the United States has an average of 38 such deaths each year of children left alone in cars.

　　Mr. Null told the USA Today newspaper that the highest number of deaths take place in July and August -- the two hottest months of the year. He said about nine children die in each of those months because they were left in a hot car. But he notes that vehicular heatstroke can happen any time of the year. He says a child can die from the heat after being left in a car when the outside temperature is as low as 14 degrees Celsius.

　　USA Today reports that 70% of vehicular heatstroke victims were children under the age of two. It says more than half of the deaths happened because the child's caregiver forgot the child was in the car. About one-third of the deaths happened when the child got in the car and was unable to get out of it.

　　The newspaper notes the temperature inside a car can reach 43 degrees Celsius when the temperature outside is 14 degrees. And it says the body temperature of a child can increase three to five times faster than adults.

　　How to Protect Yourself and Others in Extreme Heat

　　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, and hats made of natural materials.

　　Make sure the clothing is loose, permitting freedom of movement. Also, learn the danger signs of the medical problems linked to heat.

　　The most-common health problem linked to hot weather is heat stress. Usually, it is also the least severe.

　　Most people suffer only muscle pain because 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. Doctors say not to return to physical activity for a few hours because serious conditions can develop.

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

　　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. He or she will feel weak and extremely tired. They may have trouble walking normally. Heat exhaustion may also produce a fast heartbeat, breathing problems and pain in the head, chest or stomach. Doctors say people with 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.

　　Experts say even a two percent drop in the body's water supply may cause signs of dehydration. These signs include 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.

　　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 temperature increases and perspiration fails.

　　Signs of Heat Stroke, and How to Treat the Condition

　　Generally, the body temperature rises to more than 40 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 tissues and organs begin to cook when the body's temperature is higher than 42 degrees Celsius. Permanent brain damage and death may result. Someone suffering heat stroke requires immediate medical attention. Doctors say such treatment is necessary or the person could die before help arrives.

　　The purpose of immediate treatment is to cool the victim as quickly as possible to stop the temperature from increasing. Begin by moving the victim out of the sun. Raise the person's feet up about 30 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.

　　The Importance of Water

　　Experts say water is important for many reasons. Between 55 and 75 percent of the body is water. Water in blood carries hormones and antibodies throughout the body. Water in urine carries away waste materials. Water is 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 waste and perspiration. They say people should drink more than that in hot weather.

　　Experts say it is 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. During hot weather, cool liquids are best. Also, avoid sweet drinks and alcohol.

　　We need to add that doctors also say it is possible to drink too much water. Some people, for example, do this if they exercise hard during a heat wave. Experts with the Mayo Clinic say drinking too much water can cause hyponatremia. In this condition, the level of sodium in the blood falls too low.

　　The result is that the amount of water in the body increases. This causes cells to become larger. Mayo Clinic experts say the enlarged cells can cause a person to become sick or restless. They also can interfere with mental ability, make muscles weak and cause pain in the head. In a mild case, simply reducing fluids may be all that the person needs. But medical help is necessary if the condition is more severe.

　　Experts have suggestions for runners and others exercising or working hard in hot weather. They say drinking a sports drink with sodium in it can help prevent the condition.

　　Doctors say actions other than drinking water can protect against the health dangers of heat. Stay out of the sun, if possible. Wear loose, lightweight 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 health problems linked to heat. They will prevent sickness, help you feel better and may even save your life.

　　This Science in the News was written by Milagros Ardin and Christopher Cruise, who also produced today's program.

　　I'm Anna Matteo.

　　And I'm Christopher Cruise.

　　How hot is it where you are? You can leave a message on our Facebook page or visit our website: 51voa.com.com.

　　Join us again next week for more news about science on VOA Learning English.