Summer is here and it is time for fun in the sun:  picnics, beach outings, July 4th parades, outdoor sports, art fairs, music festivals.  But sometimes heat exposure and overexertion – even swimming or playing in the shade – can lead to dehydration, heat exhaustion and heat stroke; in some cases, they can be fatal. According to the Centers for Disease Control (CDC), extreme heat causes an average of 658 deaths per year, more than tornadoes, hurricanes, floods, and lightning combined.

“Heat-related illnesses and deaths are preventable,” says Ethel Taylor, DVM, MPH, lead author of a 2013 CDC study on heat-related illness. “Taking steps to stay cool, hydrated, and informed in extreme temperatures can prevent serious health effects like heat exhaustion and heat stroke.”

Everyone occasionally gets mildly dehydrated in warm weather, feeling thirsty and tired after playing, exercising or gardening. When we perspire out more than we drink in, we lose electrolytes – salts such as sodium, potassium, magnesium, and chloride that carry electrical impulses to keep our hearts, nerves, and muscles working properly. Sweating triggers the release of an anti-diuretic hormone, which tells the kidneys to conserve water, which in turn helps normalize hydration and electrolyte levels.  

The CDC advises drinking two to four 8-ounce glasses of cool fluids each hour during hot weather activities (unless a physician has advised otherwise). Water rehydrates, and drinks like Gatorade and Pedialyte help replace lost electrolytes. Avoid beverages high in sugar, alcohol, or caffeine, which can worsen dehydration, as well as very cold drinks, which can cause stomach cramps.

Without proper hydration, more serious symptoms may set in, such as profuse sweating, increased thirst, muscle cramps, and headache. If that happens, find a cool place to recover and get some fluid, advises Hallie Labrador, M.D., a sports medicine specialist with NorthShore University HealthSystem. If symptoms persist after 15 minutes, seek medical attention to avoid the onset of heat exhaustion or heat stroke.

Heat Exhaustion
Sweating in summer heat is natural; when sweat evaporates it helps keep our bodies cool.  High heat and humidity make sweat evaporation difficult, so core body temperature (around 98.6°F) can become hotter and raise the risk for heat exhaustion. The risk increases on days with a high heat index – a measure of how hot the air feels when relative humidity is factored in with the actual air temperature, according to the National Weather Service (NWS).

For example, when the outside temperature is 90°F and the relative humidity is 60%, the temperature will feel like a steamy 100°F. The NWS issues heat advisories during “excessive heat events” and cautions against strenuous activity until the coolest times of the day, usually before 10 a.m. and after 4 p.m.

Heat exhaustion symptoms include sweating and increased thirst, fatigue, rapid heartbeat, headache, clammy skin, dizziness, fainting, nausea or vomiting, muscle cramps, and confusion.

A person suffering from heat exhaustion should be moved to a cool, preferably air-conditioned place and allowed to rest so their body temperature can return to normal. The Federal Emergency Management Agency (FEMA) advises loosening or removing any restrictive clothing and applying cool, wet cloths such as towels or sheets to the person’s face and body. If the person is conscious, give small sips of cool water to drink – about a half glass every 15 minutes. As with dehydration, call a doctor or 911 if symptoms do not improve within 15 minutes.

Heat Stroke
A person whose core body temperature reaches 104°F is likely suffering from hyperthermia, or heat stroke, and needs immediate medical attention. During heat stroke the body goes into emergency cooling mode, redirecting blood flow to the skin and away from vital organs. Oxygen-deprived organs will eventually start to shut down, leading to death if not treated quickly.  

Infants, the elderly, and people with poor circulation are susceptible to heat stroke because their bodies can not easily regulate temperature. Outdoor workers, athletes, and anyone engaged in strenuous activities are also susceptible, and certain medical conditions and medications put some people at risk.

Heat stroke symptoms include body temperature higher than 103°F, taken orally; skin that is red, hot and dry (no sweating); strong rapid pulse; throbbing headache; dizziness and confusion; nausea or vomiting; or unconsciousness.

The Mayo Clinic advises calling 911 and taking swift action to cool the person down.  Move them into shade or indoors, preferably to an air conditioned space, and remove excess clothing. Use whatever means possible to cool them: help them into a tub of cool water or a cool shower; spray with a garden hose; sponge with cool water; position them near a fan (or fan by hand) while misting with cool water; place ice packs or cold, wet towels on the person’s head, neck, armpits, and groin.  Do not give fluids, in case the person can’t keep them down.  

Keep Pets Cool, Too
Pets can suffer in summer heat as well, even if they stay indoors.  Signs of heat stroke in animals, according to McCormick Animal Hospital, are heavy panting, dry or tacky nose and gums, very red gums, lying down excessively, and an unwillingness or inability to get up. 

Treatment advice is similar:  move them to a shaded area or a cool air conditioned room, give them plenty of cool water, cool them with a wrapped ice pack or by dipping them in cool (not cold) water – keeping mouth and nose above water, and call a vet. And of course, never leave pets in an automobile while it is off, in hot or cold weather.

Meg Evans has written science stories for the Evanston RoundTable since 2015, covering topics ranging from local crayfish, coyotes and cicadas to gravitational waves, medical cannabis, invasive garden...