Serious medical problems can arise when the weather affects the body’s ability to maintain a constant temperature.
In the summer of 1999, a heatwave rippled across the Midwestern United States, with temperatures exceeding 100 &176; F (37.8 &176; C). More than 250 people died, including more than 100 people in Chicago. Although the city’s death toll was high, a heat emergency plan helped the city prevent an even greater disaster.
In 1995, before the city developed the plan, a heatwave killed more than 600 people. By 1999, however, the city was better prepared to deal with weather-related emergencies. Fire stations and public libraries served as cooling stations for people without air conditioning. Police officers, public health officials, and volunteers went door-to-door to check on older people and individuals who lived alone. News broadcasters issued heat warnings and advised people on how to get relief from the heat.
Most weather-related illness and injury incidents occur because people are not aware of the risks of exposure or because they do not take precautions. In both indoor and outdoor environments, it is important to prevent, identify, and treat cold- and heat-related illnesses before they become a deadly threat.
The key to understanding the impact of hot and cold temperatures is understanding the human body’s own temperature control system. Even when it is at rest, the human body produces heat when cells break down molecules of sugars, fats, or other nutrients to obtain energy—a part of the process called metabolism.
When a person exercises, the body metabolizes more nutrients and produces even more heat. But the human body maintains a fairly constant core (internal body) temperature of 98.6 &176; F (37 &176; C) by either conserving or releasing heat. The hypothalamus, a nerve centre at the base of the brain, monitors the temperature of the blood and signals the skin and the circulatory system, the primary temperature regulators if the core temperature is too warm or too cold.
The body releases heat in four different ways. Conduction transfers heat directly from a warmer object to a colder object. When you sit on the cold ground or jump in a cold lake, your body loses heat by conduction. Convection is the transfer of heat from one place to another by the movement of heated particles.
For example, if you are outside on a windy day, the wind pushes away the air molecules around your body that have been warmed by your skin. Radiation carries heat in the form of infrared waves. If you are wearing a warm coat but not a hat in cold weather, you may still feel cold because your body is radiating heat from your head.
Evaporation, the transformation of liquid to a gas, also removes heat. In hot weather or during exercise, your body uses its supply of water to transfer heat to the surface of your skin in the form of sweat. The sweat evaporates, removing heat from your body.
Our bodies are usually able to adapt to the impact of a wide range of hot and cold temperatures. Our natural inclination to wear clothes that feel comfortable for the weather conditions helps our bodies conserve or release heat.
In extremely hot or cold conditions, however, the human body can lose its ability to control core temperatures, and our best intentions of dressing for the weather may not be sufficient. A core body temperature fluctuation of a few degrees in either direction can be deadly.
Hypothermia: Low Body Temperature
When a body loses heat to the environment faster than it can produce heat, the core body temperature drops—a condition called hypothermia. Although hypothermia affects the entire body, the cardiovascular and central nervous systems are most significantly affected. The heart rate slows, blood circulation decreases, and the brain no longer functions normally. If the core temperature drops too low, hypothermia becomes a life-threatening emergency.
Health officials often divide hypothermia cases into two categories, exposure hypothermia and urban hypothermia, even though there is no real difference in what is happening to the body.
Exposure hypothermia refers to cases among people who work or play in an outdoor setting. Many cases of exposure hypothermia happen during winter in below-freezing temperatures. But exposure hypothermia is also frequent during the summer when people are unprepared for sudden weather changes that cause temperatures to drop.
While most cases of exposure hypothermia happen to healthy, active people, urban hypothermia, cases that occur indoors in cities and towns, commonly affects the ill, very old, very young, or very poor.
These incidents account for the majority of hypothermia cases in the United States. Many of these cases occur in temperatures near 60 &176; F (15.6 &176; C), conditions that people do not often associate with hypothermia, but that are cold enough to affect an individual’s core body temperature in certain circumstances.
Some common risk factors associated with hypothermia are more prevalent in exposure cases and some in urban cases. However, it is more important to understand the risk factors in general and know why they may lead to hypothermia.
A low intake of calories and fluids significantly increases the risk of hypothermia. If the body does not have an adequate supply of nutrients, it cannot create enough heat. And if the person is exposed to cold temperatures, the need for calories increases.
If the body does not have enough fluids, the metabolism of nutrients is less efficient. According to Murray Hamlet, the director of Research Plans and Operations at the United States Army Research Institute for Environmental Medicine, a 10 percent drop in hydration (fluid levels) results in a 30 to 40 percent decrease in heat production. Also, if a person is dehydrated, the blood becomes more concentrated, leaving less blood to distribute heat throughout the body.
Consuming alcoholic beverages will not hydrate the body, and it even increases the risk of hypothermia. A shot of brandy is a traditional remedy for warming up because it creates a sensation of warmth. It actually robs the body of essential fluids, because alcohol is a diuretic, a substance that increases the flow of urine.
The alcohol also dilates (expands) blood vessels close to the skin, increasing the amount of blood that flows to the skin and subsequently, the amount of heat lost.
Illnesses and preexisting medical conditions can also increase the risk of hypothermia. People with disorders of the glandular system, diabetes, and cardiovascular disease generally do not have effective heat regulatory systems.
Also, some medications act as diuretics and therefore increase the risk of dehydration and hypothermia. Other factors such as alcoholism, illicit drug use, or untreated mental illnesses may lead people to make inappropriate judgments about risks they take in cold weather conditions.
Getting wet, either by being caught in the rain or falling in water, greatly increases hypothermia risk because water quickly removes heat from the body. A person who is submerged in water loses heat 26 to 32 times faster than he or she would in the same air temperature.
In water that is near 32 degrees F (0 degrees C), an individual will lose consciousness in less than 15 minutes. Even in water that is 60 to 70 degrees F (15.6 to 21 degrees C), a common summertime temperature of lakes and rivers, a person may lose consciousness in two hours.
The very young and very old are most susceptible to hypothermia. According to the National Institute on Aging (NIA), people more than 75 years of age are five times more likely to die from hypothermia than are those less than 75 years old. Older people are more susceptible to hypothermia because of generally poorer blood circulation, illness, and medications.
They are usually less active and therefore, do not produce as much heat. Lack of adequate nutrition and hydration and poorly heated homes are also common factors leading to hypothermia in older adults.
Children have a higher ratio of body surface area to weight. Consequently, they lose body heat more quickly in cold weather. Small children who are carried in backpacks or pushed in strollers are inactive and do not produce any extra heat. Very young children are also at a disadvantage because they may not be able to tell an adult when they are cold.
Symptoms of hypothermia and their severity depend largely upon the amount the body’s core temperature drops. Symptoms generally begin to appear when a person’s core temperature drops to about 96 degrees F (35.6 degrees C). Medical experts consider typically a core temperature below 90 degrees F (32.2 degrees C) severe hypothermia, and a core temperature below 86 degrees F (30 degrees C) leaves little hope for survival.
Hypothermia in a healthy adolescent or adult is usually easy to recognize. Buck Tilton, director of the Wilderness Medicine Institute in Pitkin, Colorado, has noted that mild hypothermia looks like “mild stupidity” because even a slight drop in core temperature profoundly affects the brain.
As the core body temperature drops, brain function deteriorates, starting with the loss of abstract thinking and progressing to the loss of motor control. A mildly hypothermic person is usually confused, lacks energy or interest, may deny the need for help, and may appear slightly drunk or disoriented.
The body reacts to the cold by constricting blood vessels near the skin and in the hands and feet, shifting blood to the body’s core organs in an attempt to keep them warm. As a result, the skin becomes pale and cool. Blood flow to the core also concentrates fluids in the body and increases urination. The brain also stimulates muscles to contract and relax rapidly—the reaction we know as shivering. This automatic behavior is the body’s way of rewarming itself.
All of the body’s attempts to stay warm can lead to a spiraling drop in temperature. An increase in urination, for example, causes dehydration. Because shivering expends large amounts of energy, the muscles will eventually run out of fuel to burn.
When a person’s core temperature drops below 95 degrees F (35 degrees C), shivering may actually begin to decrease. Other symptoms become more severe. An individual may seem unaware of the danger, become increasingly disoriented, and even hallucinate. The loss of muscle coordination results in slurred speech and stumbling.
When the core temperature drops below 90 degrees F (32.2 degrees C), the person can no longer walk or speak clearly, and shivering has usually stopped. If core temperature drops below 86 degrees F (30 degrees C), unconsciousness is likely, the skin may turn blue, the body becomes rigid, and pulse and breathing appear to stop. Few people who become unconscious due to hypothermia survive.
How to Recognize Hypothermia in Older People
Because the warning signs of hypothermia are usually easy to recognize, an unaffected person can often take steps to help a hypothermic individual warm-up and avoid the spiraling effect of heat loss. Unfortunately, symptoms of hypothermia can be difficult to identify in an older person who is indoors.
An older person may, in fact, be mildly hypothermic for weeks before collapsing from severe hypothermia. This is one reason that cases of urban hypothermia are a critical problem.
How cold older people feel is not always a good indication of their actual core temperature. Older people may have cold hands or feet because they generally have poorer circulation. They may feel cold, but have a normal core temperature.
On the other hand, many older people who are diagnosed as hypothermic have not complained of the cold, and they usually do not shiver. Symptoms of mild or moderate hypothermia common among older people may include a rigid body, hard muscle tone, an occasional fine tremor, and a cold abdomen or back. The best way to determine whether an older person is becoming hypothermic is to take his or her temperature.
How to Treat Hypothermia
Although medical attention is essential for all hypothermia cases, physicians recommend that rewarming should begin immediately for any individual who has symptoms of mild or moderate hypothermia. Begin by moving the person to a warm environment. Remove any wet clothes and replace them with layers of dry, warm clothing, blankets, or sleeping bags. Encourage the person to increase his or her activity level, because exercise can greatly increase the body’s heat production.
A person who is able to hold a cup without dropping it should drink warm, sugary liquids, which provide warmth and energy. Simply holding a warm cup can also help raise the core body temperature. Valves that control blood flow in the hands are open when the blood is warm and shut when the blood is cold.
A warm cup warms the blood, opening up the valves, increasing the blood flow, and allowing blood to transfer heat back to the body’s core. Heat packs on the hands and feet have the same effect, and placing heat packs under the arms or in the groin can also help warm the body quickly.
Skin to skin contact, such as putting cold feet in the underarms of a warm person, works effectively as well. However, vigorously rubbing hands or feet does not help warm them and can damage skin tissues that are injured by the cold.
Severe hypothermia is a life-threatening condition and requires immediate emergency medical care. If a person has lost consciousness or appears to be dead, rewarming the victim can be hazardous. When circulation is very poor, blood in the extremities, such as the hands and feet, becomes highly acidic.
If that acidic blood is propelled too quickly to the heart, the heart may stop. However, preventing any further heat loss is essential. Remove wet clothes, place blankets beneath the person, and cover the person entirely except for the face to help maintain heat. Warm water bottles or heat packs wrapped in layers of clothing can be placed by the hands and feet, but not directly in contact with them.
Physicians advise that an individual should always assume that a severely hypothermic person is alive, even if a pulse is undetectable. “They’re not dead until they’re warm and dead” is a common explanation of specialists in outdoor medical emergencies.
Therefore, a person qualified to administer cardiopulmonary resuscitation (CPR) should initiate chest compressions if there is no pulse or mouth-to-mouth resuscitation if there is no respiration or fewer than six to seven breaths per minute.
It is also important to handle a severely hypothermic person with extreme care. Rough handling can cause a condition called ventricular fibrillation, in which the heart loses its ability to pump blood to the body.
Emergency medical personnel will gradually rewarm a severely hypothermic victim with various methods, such as injecting warm fluids into blood veins or by circulating the victim’s blood through an external warming device.
Another cold-related injury often associated with cases of hypothermia is frostbite, but this injury can occur even if a person is not hypothermic. Frostbite is the freezing of skin tissues. The tissues begin to freeze when they reach a temperature of 24.8 degrees F (-4 degrees C). One of the greatest risks for frostbite is exposure to the cold air.
A below-freezing wind-chill factor (the combined cooling effect on the body of air temperature and the wind) greatly increases frostbite risk. Consequently, parts of the body that are often exposed—hands, ears, and noses—are particularly susceptible to injury. Anything that causes poor blood circulation can also contribute to frostbite. For example, if a person is wearing boots that are too tight, warm blood is not able to get to the toes.
Frostbitten skin at first appears white or grayish-yellow, or the skin may feel unusually firm or waxy. The skin is usually numb, so the victim often does not know he or she has frostbite.
To treat frostbite, the area should be warmed by skin-to-skin contact or with warm water. However, a physician should examine all frostbite injuries even if they do not appear to be severe. Frostbite can cause permanent damage to the skin. If the freezing is deep in the tissue, a part of the skin has to be removed and may need to be replaced with grafts of healthy skin. Frostbitten fingers or toes sometimes have to be amputated.
How to Prevent Cold-Related Illness and Injury
In most circumstances, cold-related illness and injury can be prevented by staying warm and dry, wearing appropriate clothing, and planning ahead for weather changes. A hat, scarf, mittens, and warm waterproof boots are important for spending any time outdoors in cold temperatures because a great amount of heat is lost from the head, hands, and feet.
If an individual is participating in outdoor activities, he or she should not assume that the exercise itself is enough to stay warm. Instead, the individual should wear multiple layers. The layer against the skin should be a wicking fabric, a fabric that draws sweat away from the skin and keeps it dry.
These fabrics include wool and specially designed synthetic materials used in outdoor gear. Middle layers of fabric should be insulating materials such as wool, down, or synthetic materials also designed for outdoor wear. The outer layer of clothing should be waterproof. Wearing layers allows the active outdoor person to remove or add layers to feel warm but not become wet with sweat.
Staying warm indoors is also important. Healthy adults need to be aware that what feels comfortable for them may not be adequate for children or old or sick people. For example, many adults prefer sleeping in cool bedrooms and turn down the heat at night during cold winter months, but cold bedrooms are very risky for infants and older adults, who do not produce as much body heat.
Eating a well-balanced diet and drinking plenty of fluids (about eight glasses of water daily) are also important steps in preventing cold-related illnesses. The best beverages for the outdoors are warm, decaffeinated teas and coffees, sweetened with honey or sugar.
Caffeinated beverages, such as hot chocolate, regular coffee, and black tea, are diuretics. Even though they are warm and often sweet, they can cause dehydration. High-calorie foods, such as energy bars and trail mix, are also good for outdoor activities because the body will have more nutrients to burn and will therefore produce more heat.
Hyperthermia: The Overheated Body
While hypothermia and frostbite result from the body losing heat faster than it can produce it, hyperthermia occurs when the body generates or gains heat faster than the body can get rid of it. Although the human body is better equipped to deal with hot temperatures than with the cold, extreme heat can overwhelm the body’s ability to maintain a normal core temperature.
The U.S. National Weather Service defines extreme heat as a temperature that is at least 10 Fahrenheit degrees above the average high temperature for a location, accompanied by high relative humidity (a measurement of the amount of water vapour in the air). The combination of extreme heat and humidity makes it impossible for sweat to evaporate. When this important cooling system no longer works well, an individual is susceptible to heat-related illnesses.
Heat-related illnesses occur along a spectrum, with mild heat exhaustion at one end of the spectrum and life-threatening heatstroke at the other end. As the body’s cooling system starts to falter, the core temperature rises. The body tries to cool itself by shifting more blood to the skin and extremities and away from core organs.
The skin becomes red and hot, and the heart begins to beat faster. A rising core temperature symptoms include nausea, fatigue, giddiness, weakness, dizziness, loss of coordination, and profuse sweating. The person may also exhibit irrational anger, poor judgment, and denial about his or her physical condition.
How to Treat Heat-Related Illnesses
If a person is promptly treated for mild heat exhaustion, he or she can recover without any permanent problems. Someone with symptoms of heat exhaustion needs to be cooled quickly. Have them stop any vigorous activity immediately and move to a cooler environment. Have the person take a cool shower or bath. Or use a spray bottle to mist the person and their clothes and fan the person to increase convective heat loss.
Heat exhaustion is not like having a fever from the flu, because different processes are happening inside the body to cause a rise in the core temperature. Therefore, heat exhaustion should not be treated with common fever-relief medications, such as acetaminophen (Tylenol).
(These medications interrupt a series of immune system reactions that were triggered by a virus and that caused the body temperature to rise.) If a person with heat exhaustion takes a fever-relief medication, it will not reduce the body temperature and may even cause other health problems.
A person with heat exhaustion should replace fluids with diluted sports drinks or a homemade solution of 1 teaspoon salt and 1 tablespoon sugar dissolved in 1 quart (1 liter) of water. A sports drink is important if heat exhaustion is accompanied by heat cramps, muscle cramps that are believed to be caused by an excessive loss of salt in sweat. Gently stretching the muscles also relieves heat cramps.
Heatstroke: A severe medical emergency
However, if heat exhaustion is not treated, it can quickly progress to heatstroke, the point at which the body’s cooling mechanisms are completely overwhelmed. Physicians generally define heatstroke as a core temperature of 105 degrees F (40.6 degrees C).
The victim usually has hot, dry skin. (If the person developed heatstroke while exercising, the skin may still be moist from prior sweating.) If a victim of heatstroke is conscious, he or she may be confused or be violently angry. Other symptoms include a rapid pulse; fast, shallow breathing; and either increased or lowered blood pressure.
Without immediate and proper treatment, the heatstroke victim may die in less than 30 minutes. Spraying with water and fanning is the most effective first-aid treatment before emergency services are available. Repeated dips in cool water are also effective. However, ice water can cause arteries and veins in the hands and feet to constrict and prevent cool blood from returning to the core.
Physicians may cool and rehydrate a heatstroke victim with an intravenous saline solution. They may also flush the digestive system with cold water or use a procedure that circulates blood outside the body, through a cooling system, and back into the body.
People who survive heat stroke almost always suffer from permanent impairment of the thermoregulatory system and damage to internal organs. In a study published in 1998 in the Annals of Emergency Medicine, most of the heat-stroke patients who were hospitalized in Chicago during the heatwave of 1995 suffered damage to the brain, kidney, and cardiovascular system. Heatstroke may also cause the breakdown of muscle tissues.
Who is at risk of Heat-Related Illnesses
Several factors can increase the risk for heat-related illnesses. Residents of urban areas are at risk because the large amounts of concrete and asphalt in a city store heat during the day and prevent cooling at night. This creates a “heat island” effect or a sort of a heat trap in which a person can never cool down adequately.
About 80 percent of heatstroke deaths occur in people who are more than 50 years old. An older person often does not sweat as much as a younger adult or does not start to sweat until temperatures are higher than temperatures that cause younger adults to sweat. An individual with heart disease is at risk for heat-related illness because of an already compromised circulatory system, and other medical conditions and medications can impair the thermoregulatory system. People who are overweight and those with an impaired ability to sweat also have difficulty getting rid of body heat.
In healthy, active adults, dehydration often triggers heat exhaustion. A dehydrated body cannot produce sweat necessary to cool the body. The amount of fluid that a person needs depends on temperature, altitude, individual physiology, and other factors. A sedentary 150-pound (68-kilogram) man in a moderate environment uses about 4 quarts (4 litres) of fluid daily, which he can easily replace by drinking and eating.
If the heat is extreme or the person is engaged in vigorous exercise, sweat production increases and fluid needs increase drastically. The consumption of diuretics, such as a cold beer or caffeinated soft drink, can greatly increase dehydration risks and cause serious heart-related problems. Children playing outside are at great risk for dehydration and heat exhaustion because they often want to stop playing even in extreme heat and do not recognize the first signs of heat exhaustion.
How to Prevent Heat-Related Problems
Staying adequately hydrated is the first line of defense against heat-related illnesses. Murray Hamlet estimates that U.S. Army soldiers drink 3 to 5 gallons (11 to 19 liters) of water a day when they are working hard in the desert. Unfortunately, thirst does not accurately indicate whether a person has enough fluids.
According to Hamlet, most people have lost about 2 percent of their body weight in fluids before they feel thirsty. After they have lost 4.2 percent of their body weight in fluids, they no longer feel thirsty. If a person continues to lose fluids, he or she will not want to eat or drink at all.
Hamlet suggests drinking by the clock rather than depending on thirst. “Develop a system to remind yourself to drink on a regular basis,” he says. Also, a better way of determining proper hydration is monitoring urine. The color should be clear or very pale yellow, and it should be plentiful.
A few dietary rules can help prevent heat-related illness. Consume salt in the form of sports drinks and salty foods such as pretzels. Salt is essential in maintaining the proper balance of fluids in the body’s cells, and profuse sweating can shed this essential mineral’s body. Salt tablets, however, should not be used.
They can be dangerous because they are too concentrated, drawing water into the stomach to dilute the salt and leaving less water in the blood. Small, frequent meals with lots of fruits, vegetables, and other foods with high water contents are better than big, high-protein meals that increase the body’s metabolism.
Appropriate clothing is also essential. Lightweight, light-coloured clothing maximizes the amount of heat that the body loses. Cotton is an ideal fabric for hot conditions because it lets air pass through, allowing sweat to evaporate. Wearing a broad-brimmed hat or carrying an umbrella offers protection from the radiant heat of the sun.
When people need to do outdoor activities in extreme heat, they should plan their activities accordingly. The midday hours are almost always the hottest and a good time to take a break from outdoor activities.
Seeking relief in an air-conditioned building, particularly during the hottest times of day, gives the body a break and allows it to cool down. Listening to weather reports is also important because broadcasters often announce the heat index and the temperature. The heat index essentially indicates what the temperature feels like when humidity is factored in.
The human body itself can develop a defence against extreme heat. Over time, it learns to disperse heat more quickly and efficiently, a process called acclimatization. However, acclimatization occurs gradually. According to Hamlet, this process takes nine days of working at a comfortable pace in extreme heat. When the body becomes acclimatized, more fluids stay in the circulatory system, sweat contains less salt, and the heart rate for any given activity slows.
Extreme temperatures, whether hot or cold, can pose an extreme danger. Cold- and heat-related illnesses do not discriminate. Although some people are at greater risk, everyone is susceptible, and everyone can take steps to prevent these illnesses. The nature of cold- and heat-related illnesses also demands that people know how extreme temperatures affect not only their well-being but also the health of others around them.