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Heat Bulletin


Periods of extremely hot weather — heat waves — can cause serious health problems for everyone. In fact, among weather-related events, heat waves are a leading cause of death. Illinois experienced this first-hand in July 1995, when extreme heat contributed to the deaths of more than 700 people in the Chicago area. Here are some commonly asked questions about hot weather and heat-related illnesses and how to safely cope with these conditions.

What is the heat index?

The heat index (HI) measures what hot weather "feels like." It is determined by the air temperature and the relative humidity. Figure 1 shows how temperature and humidity combine to produce apparent, or "feels like," temperatures.

The National Weather Service issues a heat advisory when the heat index is expected to reach 105·F during any 24-hour period and the minimum HI during that period remains 75·F or higher. A heat warning is issued when the heat index is expected to reach or exceed 115·F on at least two consecutive days and the minimum heat index during the period remains 80·F or higher.

These guidelines may be locally adjusted, however, for large metropolitan areas. In Chicago, a heat warning is to be issued when one of the three following conditions exists or is expected imminently:

  • three consecutive days with the heat index between 100·F and 105·F and either 85 percent or more sunshine on two of the three days or a minimum HI of 75·F on each of the three days;

  • two consecutive days with a heat index of 105·F to 110·F; or

  • one day with a heat index of 110·F or higher.

The National Weather Service cautions that it is important to remember that heat index values are devised for shady, light wind conditions. Exposure to full sunshine can increase these values by up to 15·F. Also, strong winds — particularly with very hot, dry air — can be extremely hazardous.

Why do high air temperatures affect the body?

Normally, the body cools itself by sweating. If temperatures are extremely high, however, sweating is not enough to maintain the body's normal temperature. When this happens, blood chemistry can change and internal organs — including the brain and kidneys — can be damaged. Heat also can be stressful if the temperature changes suddenly, since it usually takes several days for the body to adjust to heat.

What are some of the most common heat-related conditions?


What is heatstroke?

Heatstroke occurs when the body becomes unable to control its temperature: the body's temperature rises rapidly, the sweating mechanism fails and the body is unable to cool down. Body temperature may rise to 106·F or higher within 10 to 15 minutes. Heatstroke can result from overexposure to direct sunlight, with or without physical activity, or to very high indoor temperatures. It can cause death or permanent disability if emergency treatment is not given.

What are the symptoms of heatstroke?

Symptoms of heatstroke include an extremely high body temperature (above 103·F, orally); red, hot and dry skin; rapid pulse; throbbing headache; dizziness; nausea; confusion; and unconsciousness.

How is heatstroke treated?

If symptoms of heatstroke are present, find a cool place, preferably an air-conditioned indoor setting. Outside, find a spot in the shade. Put the person in a semi-sitting position. Loosen his or her clothing and bathe the head and body with COLD water. Seek medical attention immediately.

What is heat exhaustion?


What are the symptoms of heat exhaustion?


How is heat exhaustion treated?


How can I avoid heat exhaustion and heatstroke?

Try to keep cool during extremely hot weather. Stay in a cool environment (preferably air conditioned), drink plenty of fluids — such as water, fruit juices or fruit drinks — and use common sense. Heat injury may develop with or without feelings of discomfort.

What if I do not have an air conditioner?

Seek out the nearest facility that is air conditioned, such as a cooling shelter, a senior citizen center, a church, the local YMCA or a center designated by your community. Even short periods of time in a cool environment will lessen the risk of heat injury. Fans alone will not effectively cool an overheated person when air temperatures are above 90 ·F.


What is "plenty of fluids"?

"Plenty of fluids" means at least 1½ to 2 quarts of fluids daily. This can be water, fruit juice, or fruit-flavored or carbonated drinks. Since aging can cause a decreased thirst sensation, elderly persons should drink water, fruit juices or other fruit drinks at regular intervals during the day, even if they do not feel thirsty. Avoid alcoholic beverages and those containing caffeine. Salt tablets are not substitutes for fluids.

Who is most at risk for heat-related problems?

Anyone can develop heat-related problems if air ventilation is not adequate or if the person is overexposed to direct sunlight. However, certain groups of people are at increased risk during extremely hot weather. These include elderly persons living alone, people with chronic medical conditions, and persons taking certain medications.

What kinds of medications cause special heat-related problems?

A number of different kinds of medications can pose special problems during periods of extremely hot weather. These include diuretics (water pills), many heart medicines, diabetes medicine (tablets and insulin), psychoactive drugs (antidepressants and mood altering drugs), antihistamines (hay fever and allergy medicine) and antihypertensive (high blood pressure) drugs. Do not change or discontinue prescribed medications without advice from your physician.

How does living alone increase the risk of heat trauma for the elderly?

Heat-induced illness can result in confusion, dizziness and loss of consciousness. This is why it is important that friends and relatives have daily contact — and not just telephone contact — with an elderly person who lives alone.

What about children? Can they get sick from the heat?

Yes. Young children, particularly infants, are extremely sensitive to heat and can easily become dehydrated (lose more body fluids than usual) from high air temperatures. To help avoid dehydration during extremely hot weather, adults should make sure children drink plenty of fluids. Young children should be kept out of direct sunlight.

What are some good tips on how to avoid heat-related problems?





