Last reviewed by Faculty of Harvard Medical School on January 24, 2013
By Harvey B. Simon, M.D.
Harvard Medical School
Global warming is on everyone's mind, as it should be. But even before climate changes kicked in, summers were hot. And whatever the future holds for our environment, summer's heat is as predictable as winter's chill.
Summer's heat can be a killer. In an average year, 208 Americans die from heat-related illnesses. During extreme summer temperatures, the toll can double. Many more people suffer less severe heat-related illnesses.
Heat may be inevitable, but heat-related illness is not. A few simple precautions can protect you from becoming a seasonal statistic.
Back to top
How the Body Stays Cool
Even on a crisp November day, your body has to work at staying cool. That's because it generates heat as a byproduct of all its metabolic processes. If you retained that heat, your temperature would climb nearly two degrees each hour.
To prevent over-heating, your body is constantly getting rid of excess heat, mostly through your skin. But to do that effectively two things must happen.
First your circulation must be able to pump plenty of blood to your skin. This raises your skin temperature and brings the heat to the surface. Second, the air must be cooler than your blood, so the heat transfers from your body into the cooler surrounding air. (This process is called conduction.) Add a cooling breeze and the movement of the air also helps to release body heat. (This process is called convection.)
Under normal circumstances, conduction is an efficient way to lose heat. That's why you take off your shirt in summer and put on a sweater in winter. But when the air temperature approaches your body temperature, or when exercise sends your body's heat soaring, conduction won't do the trick. Now evaporation kicks in. You'll sweat profusely, and as it evaporates, sweat will carry away your excess body heat. But as humidity climbs, evaporation slows, then stops.
Back to top
Types of Heat-related Illnesses
Heat-related illnesses result from an imbalance between man and nature. Nature provides high air temperatures, high humidity, the radiant energy of sunlight and still air. You can't do much to change nature, but you can control the human elements that contribute to heat-related illnesses: undue exposure to sun and heat, unwise exercise, inappropriate clothing and dehydration.
Although mental irritability is the most common reaction to conditions that are too darned hot, grumpiness does not qualify as a true heat-related illness. But here are three medical conditions that do:
- Heat cramps. It's okay to dismiss the occasional muscle cramp as a simple "charley horse," but if you get recurrent cramps in hot weather, you could be heading for trouble. Heat cramps signal dehydration severe enough to deprive muscles of the extra oxygen they need to exercise. The remedy: Slow down, tank up with cool water, stretch out, gently massage the tight muscle, and get out of the heat.
- Heat exhaustion. Heat cramps are painful but not life-threatening. That's because body temperature is normal even though muscles are in spasm. But in heat exhaustion, body temperature is often above 1030. That can lead to weakness, lethargy, loss of concentration, headache and nausea, along with muscle cramps.
Heat exhaustion impairs mental clarity and judgment, so you may not recognize what is happening. Be alert for early symptoms and take corrective action as soon as they appear. Look for signs of heat exhaustion in others, too: Confusion, profuse sweating, and flushed, clammy skin are among the tip-offs. Move the person to a cool place as soon as possible; remove his clothing and fan him en route. Apply ice packs if they're available. If not, use wet towels. Cool fluids on the skin will lower body temperature, but it's even more important to get them down the hatch. Don't force someone who is weak and confused to drink too much too fast, but keep encouraging the person to drink until they are re-hydrated.
- Heat stroke. This illness kills people each and every summer, even with treatment. There are two types of heat stroke.
- Classic heat stroke This is also called epidemic heat stroke because it's the most common type during heat waves. It typically affects elderly people who stay in their stifling apartments without air conditioners or fans. Many have chronic illnesses such as diabetes, and some take medications that reduce their ability to sweat.
- Exertional heat stroke This is also called sporadic heat stroke because it occurs in isolated cases rather than community-wide outbreaks. The typical victim is a man who exercises vigorously in the first few days of a hot spell. Many victims are young, but most are out of shape. Marine recruits and "weekend warriors" are good examples of men at risk. Wearing heavy clothing, exposure to direct sunlight and dehydration often add fuel to the fire.
Heat stroke is a medical emergency. It starts out looking like heat exhaustion, but its symptoms are more severe and they progress more quickly. Lethargy, weakness and confusion evolve into delirium, stupor, coma and seizures. Body temperature rises drastically, often exceeding 105o or 106o. Even with so much excess body heat, the person's skin may be pale and inappropriately dry because the ability to sweat normally has failed.
Heat stroke kills because it damages the heart, liver, kidneys, brain and blood clotting system. Survival depends on getting quick and aggressive emergency treatment. Expert metabolic and cardiovascular care is mandatory, but even in this era of high-tech medicine, the best way to lower a heat-stroke patient's temperature is to immerse him in a bath of ice water or to spray him with cold water and turn on a strong fan.
Back to top
Preventing Heat-related Illnesses
An ounce of prevention will go a long way, but for heat-related illnesses, a quart is even better. That's because hydration is essential, and it takes a lot of liquid to preserve your body's circulation and replace the fluid lost in sweat. Even if you're sedentary, you may need 10 to 12 cups of water a day; if you exercise, you'll need much more. Cool liquids are best. Despite the popularity of sports drinks, nothing beats water.
Hydration is necessary, but it's not sufficient to stave off summertime heat. Here are a few important additional tips:
- Get away from the heat. An air-conditioned room is best, but even a fan will help. If you can't cool your own home, find a friend or relative to stay with. Some communities provide emergency cooling centers during heat waves.
- Stay out of the sun and avoid the midday heat as much as possible. Wear brief, loose-fitting, light-colored garments.
- Don't exercise when it's hot and humid. If it's humid and above 80o to 85o, jump in a pool or work out in an air-conditioned gym. If you exercise outdoors, do it in the early morning or evening. Slow down; walk instead of jogging or use a cart instead of walking the golf course. Take breaks and quit early.
- Above all, listen to your body. Muscle cramps, fatigue, weakness, impaired concentration, confusion, lightheadedness, nausea, labored breathing, chest discomfort, and a rapid or erratic pulse can all be signs of trouble. Listen to your body's warning signals; if you feel even a little ill get to a cool place, drink plenty of cool water, and be sure help is available if you don't start to feel better promptly.
Back to top
The Good, Old Summertime
Even with an occasional hot day, summer is a wonderful season. The days are long, the nights are comfortable, and the hectic pace of modern life slows down a bit. But summertime can cause health problems, ranging from sun exposure and poison ivy to insect bites and air pollution. Among summer's seasonal hazards, heat is the worst particularly when it lingers day after day.
To keep the living easy this summer, understand how your body handles heat, listen to warnings from the weather service and your body, and take all necessary precautions. It's the cool thing to do.
Back to top
Harvey B. Simon, M.D. is an Associate Professor of Medicine at Harvard Medical School and a member of the Health Sciences Technology Faculty at Massachusetts Institute of Technology. He is the founding editor of the Harvard Men's Health Watch newsletter and author of six consumer health books, including The Harvard Medical School Guide to Men's Health (Simon and Schuster, 2002) and The No Sweat Exercise Plan, Lose Weight, Get Healthy and Live Longer (McGraw-Hill, 2006). Dr. Simon practices at the Massachusetts General Hospital; he received the London Prize for Excellence in Teaching from Harvard and MIT.