Dear Doctors: Can you please explain why hot weather is so dangerous? We had a few heat waves with high humidity, and my grandfather didn’t even realize he was suffering from heat exhaustion. Air conditioning is not common in our area and our children also have difficulty. Honestly, it’s a little scary.

Dear Reader, A series of extreme heat waves, often accompanied by high humidity, are making summer difficult for much of the United States. Even regions with generally mild climates are being hit hard. The result has been a sharp increase in heat-related illnesses, hospitalizations and, tragically, deaths. This happens because, in order to function properly, warm-blooded creatures need their core temperature to stay within a narrow range. For humans, it’s somewhere in the neighborhood of 97 to 99 degrees Fahrenheit.

When ambient temperature, physical activity, or a combination of the two cause overheating, our bodies use various physiological processes to attempt to cool themselves. The first are reddening of the skin and sweating. The first sends blood to the surface of the skin in order to cool it, and the second moistens the skin itself, allowing an evaporation and cooling effect.

But when temperatures are high enough, flushing cannot cool the blood. And on humid days, when water saturates the air, sweat evaporates much more slowly, if at all. With the body’s natural cooling systems overridden, the core temperature begins to rise. This marks the advent of an increasingly serious range of heat-related illnesses.

The milder of these illnesses, also known as hyperthermia, are heat-related dizziness or fainting and heat cramps. When these occur, the person should stop all activity, move to a cool, shady place, and gradually drink water to rehydrate.

A serious set of heat-related symptoms is known as heat exhaustion. It is characterized by dizziness, profuse sweating, clammy skin, headache, exhaustion, weak and rapid pulse, decreased urine output, slightly elevated body temperature, and sometimes nausea or vomiting.

In addition to following the steps above, a person suffering from heat exhaustion should directly cool their skin. This can be done with a cold bath or shower, or by misting or blotting the skin with cold water.

If left untreated, heat exhaustion can quickly lead to heat stroke. These symptoms include hot to the touch and often dry skin, body temperature of 104 degrees Fahrenheit or higher, mental confusion, loss of consciousness, and a rapid pounding pulse. Heat stroke is an emergency. Immediate medical attention is needed to prevent brain damage, organ damage, and even death.

Never ignore any form of heat-related illness – even the mildest form can escalate into a medical emergency.

In this time of unusual summer heat, it’s important to have a heat safety plan. Learn about the different options for staying cool that are available in your community. This includes air-conditioned public spaces such as shopping malls, public libraries and senior centers. Many communities open dedicated cooling centers during a heat wave. Keep up to date with weather reports. Whenever a heat wave hits, stay safe by putting your safety plan into immediate action.

Send questions to [email protected], or write to: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Due to volume of mail , no personal answer can be provided.