It's peak summertime, a time for outdoor activities, back-to-school barbecues, and fall sports! However, it's also the time of greatest risk for heat-related illness. Statistically, July and August are the warmest months for the contiguous United States. According to the Environmental Protection Agency (EPA), extreme heat is the leading cause of weather-related deaths in the United States. In 2023, extreme heat resulted in 294 deaths and 1,862 heat-related injuries.
In August 2024, the rate of heat illness among active-duty service members in the United States was 6.8 cases per 1,000 individuals. This decreased from the peak in 2023, with 668 diagnosed heat illnesses (which included 581 heat exhaustion cases and 87 heat stroke cases).
Geographically, the US's Southwest, Southeast, and South regions experience the most heat days; however, heat-related illnesses can occur anywhere and affect anyone. Recognizing the signs, symptoms, treatment options, and prevention strategies is important to safely enjoy your outdoor summer activities.
What Happens During Heat-Related Illness
Normally, when the body gets hot, it cools itself by sweating, and the evaporation of the sweat helps to cool the body. Additionally, blood flow is redistributed to the skin's surface to release the heat. This is why a person who is hot will appear flushed. Heat illness can occur when these thermoregulatory mechanisms get overwhelmed.
Causes of Heat Illness
- Hot and Humid Weather: This decreases the body's ability to cool down by sweat evaporation.
- Strenuous Exercise: increases the body's metabolic heat, thus increasing the risk of overheating. This can also apply to laborers and military personnel who are required to perform strenuous physical activity.
- Insufficient Hydration: This impairs the body's ability to produce sweat and cool itself.
- At-Risk Populations: Infants and children under four, as well as older adults over 65, are at a higher risk for heat illness. Obesity and certain medications can also interfere with the body's thermoregulation, increasing the likelihood of heat illness.
Types of Heat Illness, Symptoms, and First Aid
Heat Rash
Heat Rash is a skin irritation caused by excessive sweating during hot and humid weather.
Heat Rash Symptoms:
- Red clusters of bumps or small blisters
- Often found on the neck, chest, groin, under the breasts, and elbow creases.
First Aid:
- Keep the rash area dry. Use powder to decrease moisture. Do not use creams or ointments.
Heat Cramps
This is the mildest form of a heat-related illness. If unrecognized, it may lead to heat exhaustion or stroke. Heat cramps typically occur during or following physical activity in a hot environment because of the loss of electrolytes and fluids through sweating. Sweating depletes the body's salt, which can cause the muscles to cramp.
Heat Cramps Symptoms:
- Painful cramps or muscle spasms in the legs, arms, or abdomen.
- Heavy Sweating
First Aid:
- Drink water and have a snack or sports drink that replaces carbohydrates and electrolytes. Repeat this every 15 minutes until the symptoms subside. Ensure the sports drink contains sodium to replenish the body's salt lost through sweating.
- Rest in a cool place
- Gently massage the affected muscles
- Seek immediate medical attention if cramps last longer than 1 hour
Heat Exhaustion
Heat Exhaustion is more severe than heat cramps and results from longer exposure to high temperatures. This is especially true when combined with high humidity and strenuous physical activity. Heat exhaustion can occur when the body loses excessive water and salt through sweating but cannot adequately cool itself. Core temperatures of heat exhaustion are typically between 101and 104degrees Fahrenheit.
Heat Exhaustion Symptoms:
- Heavy Sweating
- Cool, pale, clammy skin
- Headache
- Nausea/vomiting
- Dizziness
- Weakness
- Irritability
- Thirsty
- Heavy Sweating
- Increased body core temperature
- Decreased urine output
- Fainting
First Aid:
- Get out of the heat
- Loosen or remove excess clothing
- Cool down by applying ice packs to your skin (armpits, groin, back of neck), soaking towels in ice water and placing them on your skin, or pouring water on the skin and fanning.
- Slowly sip water to rehydrate
- Seek medical attention if the person vomits, symptoms worsen, or last longer than 1 hour.
Heat Stroke
Heat stroke is the most severe heat-related illness and a true medical emergency. During heat stroke, the body can no longer control its temperature. Without thermoregulation, the body's core temperature rises rapidly, stops sweating, and can lead to permanent organ disability or death. Heat stroke occurs when the core temperature exceeds 1040F.
Heat Stroke Symptoms:
- No longer sweating
- Hot, red, dry skin
- Rapid and strong pulse
- Confusion, slurred speech
- Dizziness or fainting,
- Throbbing headache
- Possible seizures
First Aid:
- Call 911 or get the person to the hospital immediately. Delay of treatment can be fatal!
- Move the person to a cooler area (preferably into an air-conditioned space).
- Cool the body down by the means described above
- Do NOT give them fluids, as they may choke or aspirate
- Do not try to give them any fever-reducing medications (they will not help and may worsen complications)
- The person with heat stroke needs rapid cooling and IV fluids replacement at a hospital!
Rhabdomyolysis
Rhabdomyolysis is a medical condition associated with heat illness and prolonged exercise. It causes the rapid rupture, breakdown, and death of muscle tissue. When the muscle tissue dies, it releases electrolytes and protein into the blood, leading to arrhythmias, seizures, and kidney damage.
Rhabdomyolysis Symptoms:
- Server muscle cramps/pain
- Dark urine (tea or cola colored)
- Weakness
- Exercise intolerance
- May be asymptomatic
First Aid:
- Stop the activity
- Drink liquids (preferably water)
- Seek immediate medical care
- A blood sample will be analyzed for creatine kinase
Prevention
With some simple preventative tips, you can help avoid heat-related illness and continue to enjoy your summer outdoor time.
Hydrate
You can help prevent heat-related illness by drinking plenty of water and staying hydrated. Most people think they drink enough, but do not. Generally, a person should drink 8 cups (64 oz) of water daily. As the temperature rises, this needs to be increased. Additionally, sweating depletes salt and minerals from your body- make sure to replenish these with beverages that contain electrolytes and salt. Hydration doesn't always have to come from drinking. Eat foods with high water concentrations like watermelon, cucumbers, berries, etc!
Wear light clothing and sunscreen.
Choose lightweight, light-colored, and loose-fitting clothing. Clothing with UVA protection is readily available now. Wear sunscreen, and remember to reapply as directed.
Choose when to be outdoors.
If possible, try to schedule your outdoor activities before noon or in the evening to avoid the hottest times. Try to find locations that allow you to rest in shady areas often.
Pace Yourself
If you are not used to working or exercising in hot weather, start slowly and gradually increase. Schedule breaks regularly and frequently. Stop if you feel short of breath or show any signs or symptoms of heat illness.
Exercise in the heat
For people who will be exercising in the heat, the National Athletic Trainers Association (NATA) provides the following guidelines to prevent and manage exertional heat illness in athletes. NATA recommends activity modifications based on wet bulb globe temperature (WBGT) readings, which take into consideration temperature, humidity, wind speed, sun angle, and cloud cover.
According to the NATA, there should be at least three rest breaks of 4 minutes or more each hour for exercise in WBGT of 82.0-86.9 degrees Fahrenheit. If the WBGT reading is 87.0-89.90 degrees Fahrenheit, exercises should not exceed 2 hours, and at least four rest breaks of 4 minutes or more should be provided per hour. If a person plays an equipment-laden sport like football, the equipment should be removed for conditioning.
For WBGT between 90.0 and 92.0 degrees Fahrenheit, a maximum exercise time of one hour is recommended, with 20 minutes of rest breaks during that hour of exercise or practice. No outdoor workouts are recommended for WBGT readings over 92.1 degrees Fahrenheit. The problem with using WBGT measurements is that specialized equipment is required to obtain the reading.
Conversely, the National Weather Service uses the heat index, which combines air temperature and humidity to determine how hot it feels (NWS, n.d.b). Many people know heat index measurements, which are often broadcast or published and are more readily available to the public than WBGT.
A chart on the NWS website provides a correlation to possible heat illness potential at different heat index temperatures. Unfortunately, there is no reference to the exercise duration according to different heat index measurements. While a heat index between 103 and 124degrees Fahrenheit is listed in the Danger category, there is no definitive temperature to stop exercising outdoors completely.
Conclusion
Heat illness is a serious and preventable condition that can be effectively managed through education, proper hydration, acclimatization, and early recognition of symptoms. By implementing proactive measures and promoting awareness, individuals and communities can significantly reduce the risk of heat-related health emergencies.
About the Author
Dr. Cindy Endicott is a Doctor of Physical Therapy specializing in orthopedic and sports physical therapy. Cindy joined CEUFast, Inc. in 2023 as a course planner. She has been a Fellow of the American Academy of Manual Physical Therapists since completing her Certification in Orthopedic Manual Therapy and Diploma in Manipulative Therapy, including advanced manipulations modules. She has 18 years of experience working in collegiate sports medicine and seven years in outpatient physical therapy practice.
She is currently a United States Olympic and Paralympic Center volunteer sports medicine provider. She has worked with the following Olympic National Governing Bodies: USA Taekwondo, Soccer, Men's Paralympic Soccer, Boxing, Wrestling, Cycling, Gymnastics, Judo, and Volleyball. She traveled as a team physio and athletic trainer for USA Taekwondo with the Olympic Senior National Team between 2013 and 2019, with extensive international travel to elite tournaments, world championships, and Olympic qualification events. She is on the medical advisory committee and a provider for USA Ultimate.
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