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Extreme hot weather in India and Pakistan has led to hundreds of deaths. Several hot days that follow each other are considered a heat wave. The most common health problem linked to hot weather is heat stress. It is also the least severe. Heat stress causes muscle pain. The pain warns the body that it 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. 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. They feel weak and extremely tired. Heat exhaustion may also produce a fast heartbeat, breathing problems and head, chest or stomach pains. Doctors say patients should rest quietly in a cool place and drink plenty of water. It may help to wash with cool water. Experts say even a two percent drop in the body’s water supply may cause dehydration. This can mean problems with memory and even simple mathematics. The treatment for dehydration is the same as for heat exhaustion. Drink plenty of water and rest in a cool place. To avoid dehydration people should drink about two liters of water a day. Heat stroke is the most serious disorder linked to hot weather. It happens when the body cannot control its temperature. The body temperature increases to more than 40 degrees Celsius and stops perspiring. The skin becomes dry and very hot. A person may not know what is happening. In extreme cases, permanent brain damage and death may result.