The ill effects of heat kill more people in the U.S. than those of any other weather phenomenon, according to the National Weather Service. And globally the growing number of longer-lasting and hotter heat waves because of climate change has left people more vulnerable to record-shattering highs.
So beyond running through a sprinkler and drinking ice-cold lemonade, how can you keep cool when temperatures soar? Scientific American spoke with experts in environmental health and medicine about how to recognize the health risks associated with extreme heat and what you can do to stay safer during heat waves.
Who is most vulnerable to extreme heat?
Generally, older people, pregnant people and children have more difficulty regulating body temperature and are more susceptible to heat illness. Asthma, cardiovascular disease, mobility limitations and other health conditions also can exacerbate illness associated with heat.
In addition, prescription drugs can play a role. “There are a lot of drugs that predispose you to heat illness,” says Edward Walter, an intensive care specialist at Royal Surrey County Hospital in England. “They interfere with the way that you lose heat,” disrupting your body’s capacity to sweat or retain water. These drugs broadly include some antidepressants (particularly certain selective serotonin reuptake inhibitors, or SSRIs, such as Prozac, tricyclics such as Elavil, atypical antidepressants, antipsychotics and cardiovascular medications.
People whose job requires them to spend extended periods of time outdoors, such as agricultural and construction workers, are at higher risk of heat-associated illness. Those living in areas of the world with a climate that was moderate until recent years may also be less prepared for an extreme heat wave. For example, only 3 to 5 percent of homes in the U.K. were estimated to be equipped with air-conditioning between 2013 and 2019. And historically marginalized communities are often relegated to neighborhoods with the most oppressive summertime heat in a given U.S. city, in part because of redlining—a set of racially and ethnically discriminatory home-loan and other policies that were widespread in the mid-20th century. “In the United States, we know, for example, that redlined districts are hotter than the surrounding areas because fewer trees were planted as part of the redlining process,” says epidemiologist Kristie Ebi, who specializes in environmental and occupational health at the University of Washington. As a result of many such practices, socioeconomic status and race are often correlated with heat-related illness.
What’s the difference between heat stroke and heat exhaustion? When should I seek medical attention?
Clinicians use a three-stage system to categorize heat illnesses. The first and mildest stage is heat cramps, which are characterized by involuntary muscle spasms. They often occur during exercise. Stage two is heat exhaustion, which is accompanied by a rapid pulse, heavy sweating, and occasionally nausea and intense fatigue.
Heat stroke is the third and final stage of heat illness. “Heat stroke is a very serious medical condition,” Ebi says. It can come on suddenly and turn deadly if left untreated. With heat stroke, a person’s skin may become hot and dry to the touch, they may vomit or feel dizzy, and their internal body temperature can climb as high as around 105 degrees Fahrenheit (41 degrees Celsius). People with these heat symptoms should seek medical treatment immediately.
“One of the first symptoms many people experience when they’re getting into trouble with heat is confusion,” Ebi says. If your mind starts to feel muddled during a heat wave or you notice a loved one acting dazed, it’s probably time to head to the hospital or health clinic or to call a medical professional. Similarly, seek help if you suddenly stop sweating: it could be a sign of dangerous dehydration, which can lead to kidney damage. Under no circumstances, Walter says, should people with any of these heat symptoms try to “tough it out.” Heat illness “is a much more significant and long-term illness than we realize,” he adds. Along with the kidneys, heat stroke can damage the circulatory system and brain, leading to heart disease or cognitive troubles later in life.
How can I keep cool during a heat wave?
Simple interventions to prevent heat-related illness include “staying hydrated, staying out of direct sunlight” and staying indoors if air-conditioning is available, says Quinn Adams, an environmental health researcher at Boston University. Ebi adds, “You could put a damp towel around your neck or sit in front of an electric fan and squirt water on yourself so that the water evaporates and helps you feel cooler.”
If you do start to become overheated, cool down your core rather than focusing on extremities such as the hands and feet, Walter says. That way you avoid restricting blood flow to certain body parts, such as your arms, as your muscles contract from the cold. If possible, submerge your whole body in cool but not freezing water to quickly bring down your core temperature.
High heat can be particularly dangerous at night, when your body needs to rest and recover. Climate change is raising nighttime temperatures, too, which can interrupt the sleep cycle—an additional health risk. On hot nights, sleep in light, breathable fabrics and in a well-ventilated room to dissipate body heat.
What if the power goes out?
If you lose power or live in a home without air-conditioning, Adams recommends checking your area for local cooling centers. These large, air-conditioned public spaces are available in most major cities during summer months. “It’s a very important intervention,” she says. “And oftentimes they go underutilized.”
If a cooling center is not available in your area, stick to the basics: staying hydrated, avoiding direct sunlight and generating air flow. Whether it means opening doors and windows or simply using a magazine or flier as a handheld fan, “changing the air current seems to be pretty effective,” Walter says.
What can my city do to better adapt to heat waves?
In the short term, Adams recommends initiatives to plant more shade trees, which reduce the urban heat island effect, as well as subsidies for air-conditioning units and systems. Developing and implementing a citywide action plan that includes early-warning systems for heat waves can increase awareness and help avoid unnecessary deaths from extreme heat.
Ultimately “the most obvious choice would be to reduce our dependence on fossil fuels,” Adams says. “Climate change is not a problem of the future. It’s happening right here and right now, and it’s affecting the health of our communities.”