Heat exhaustion is usually caused by losing too much water and salt from the body in hot weather, especially when the person affected has been taking part in vigorous physical activity. It may develop into heat- stroke if the person becomes so dehydrated that he or she stops sweating, with the result that body temperature rises dangerously.
Heat exhaustion generally makes someone feel weak, thirsty and nauseous; there may be a headache and muscle cramps, and dizziness on trying to stand up. If these symptoms occur it is extremely important to take adequate measures in order to prevent a heatstroke. These include drinking plenty of water, taking enough salt and moving to a cooler place. The opposite problem, cooling down too much, must be handled with as much care as heat exhaustion. After prolonged exposure to cold, more body heat may be lost than can be replaced, so the body temperature drops dangerously low. This phenomenon is known as hypothermia.
Babies and old people are especially vulnerable to hypothermia; they may lose a dangerous amount of body heat in conditions that may cause no problem to an adult. In old people, hypothermia may easily be mistaken for a stroke or heart attack. The victim should be warmed gradually by taking him or her into warm surroundings. A baby who has become dangerously cold is drowsy, floppy, and unable to feed. The skin of hands, feet and face may be bright pink. Try to rewarm the baby gradually by holding him or her against your body after removing the clothes in between.
Frostbite may occur in adults as well on exposed parts of the body or on extremities such as the face, hands and feet in very cold weather. The skin turns hard, cold and white, and by this stage the part is usually numb rather than painful. The best first aid for minor frostbite is slowly to warm the affected part by contact with a warm body part or in (not too) warm water. For instance, you should try, once under shelter, to warm frostbitten feet or hands in the armpits of either the casualty or another person.