Heat Illness vs. Heat Stroke: How Wet Bulb Globe Temperature Affects Your Health
Table of Contents
Feeling the Heat—Understanding the Impact of Extreme Temperatures on Our Health
Picture a sweltering summer day where the sun is so intense that the mere thought of stepping outside makes you pause. The kind of day where ice cream barely makes it from the cone to your mouth before it drips onto the scorching pavement. On days like these, the heat isn’t just uncomfortable; it’s a force to be reckoned with—a silent but powerful threat to our health.
As our world warms and climate change brings more frequent and severe heatwaves, the reality of extreme heat becomes an inescapable part of our lives. We might talk about temperatures in numbers—95°F, 100°F—but those numbers don’t capture the true experience of the heat. They don’t describe the way the air feels heavy, how your clothes stick to your skin, or how just a few minutes outside can leave you drenched in sweat. To really understand the risks, we need to go beyond the temperature and look at what those numbers mean for our bodies.
This is where the Wet Bulb Globe Temperature (WBGT) comes in. It’s a term that might sound technical, but it’s about something very human—the way we feel the heat and how it affects our ability to stay safe and healthy. WBGT takes into account not just the air temperature, but the humidity, wind speed, and sunlight—the elements that make us sweat, that push our bodies to the brink. On days when the WBGT rises, the risk of heat-related illnesses climbs with it, turning a hot day into a dangerous one.
At Air Support Project, we know that understanding WBGT is key to protecting ourselves and our loved ones. It’s not just about knowing the numbers; it’s about feeling the heat and recognizing when it’s time to take action. Whether you’re caring for a child, an elderly relative, or yourself, being aware of WBGT can mean the difference between staying safe and facing serious health risks.
As you read on, remember that this isn’t just about statistics or science—it’s about the real, tangible ways that heat affects our lives. It’s about feeling that oppressive heat and knowing how to respond, so that even on the hottest days, you can keep yourself and your family safe.
As summer weather becomes more extreme and the impacts of climate change become more pronounced, it is crucial to prepare for the heat. Climate change is leading to longer and hotter summers, as well as extreme weather events in locations that may not be adequately prepared for such conditions. This intensifies the challenges of maintaining good indoor air quality (IAQ). At Air Support Project (ASP), our goal is to provide accessible information on IAQ. Understanding the difference between heat illness and heat stroke is vital for protecting vulnerable groups; including children, pregnant people, the elderly, individuals with certain chronic conditions, and outdoor workers. Here’s what you need to know to stay safe during the hotter months, with a special focus on wet bulb globe temperature (WBGT) and its significance.
Understanding Wet Bulb Globe Temperature
Wet bulb globe temperature is a metric combining temperature and humidity to reflect the true impact of heat on the human body. Unlike regular temperature readings, WBGT impacts the body’s ability to cool itself through sweating. When WBGT rises – especially above 35°C (95°F), which typically aligns with a heat index of 55°C or 131°F – the body’s natural cooling mechanisms become less effective, leading to an increased risk of heat-related illnesses. This is a helpful link to calculate WBGT and this interactive WBGT map.
Let’s take a step back and differentiate between WBGT and heat index. The heat index considers temperature and relative humidity to estimate how hot it feels to the human body. WBGT factors the additional measures of radiant heat and wind speed to determine the level of heat stress induced by these environmental conditions. A WBGT above 90 degrees is the most extreme category of heat stress, in which outdoor activity should be severely limited and avoided. A WBGT of 95 degrees is considered to be a hard threshold of human survivability – in these environmental conditions, the human body can no longer cool itself through sweating, and prolonged exposure is fatal [1].
The Impact of Wet Bulb Globe Temperature on IAQ
The high heat index and humidity that occur during times of elevated WBGT can exacerbate air pollution, increasing levels of ground-level ozone and particulate matter. This not only affects outdoor air quality, but can also infiltrate indoor environments, compromising the air we breathe inside our homes and workplaces [2]. The presence of fine particulate matter (PM2.5) can be particularly harmful as these particles can penetrate deep into the lungs and even enter the bloodstream, causing a range of health issues.
Ground-Level Ozone and Particulate Matter
- Ground-Level Ozone: Formed when pollutants emitted by cars, power plants, and other sources react in the presence of sunlight. High WBGT accelerates this chemical reaction, leading to higher concentrations of ozone, which can cause respiratory problems and other health issues [3].
- Particulate Matter: Fine particles from vehicle exhaust, industrial emissions, and natural sources such as wildfires. These particles are often classified by size, with PM10 being particles with diameters of 10 micrometers or smaller, and PM2.5 being particles with diameters of 2.5 micrometers or smaller. PM2.5 particles are particularly harmful, as they can penetrate deep into the lungs and even enter the bloodstream, causing a range of health issues. High humidity levels associated with high WBGT can increase the amount of particulate matter in the air, further degrading air quality [4].
To mitigate these impacts, use air purifiers indoors and regularly check local air quality reports. Using high-efficiency particulate air (HEPA) filters or filters rated MERV 13 or higher in your air purifiers can significantly reduce the infiltration of outdoor pollutants [5].
However, during extreme WBGT events, the primary concern should be avoiding heat stress. In such conditions, staying indoors in air-conditioned environments is crucial, as outdoor exposure can rapidly lead to dangerous heat-related illnesses. Staying cool and hydrated is essential during these extreme heat events, and avoiding unnecessary outdoor activities can significantly reduce the risk of heat stress.
Recognizing Heat Illness
Heat illness encompasses a range of conditions caused by exposure to high temperatures. The most common types are heat cramps, heat exhaustion, and heat stroke. Understanding the symptoms and differences between these conditions can be lifesaving, particularly when WBGT is high [6].
Heat Cramps
- Symptoms: Muscle pains or spasms, usually in the abdomen, arms, or legs.
- Action: Stop physical activity, move to a cooler place, drink water, and stretch or massage the affected muscles. Replenishing electrolytes with a sports drink can also help [7].
Heat Exhaustion
- Symptoms: Heavy sweating, weakness, cold, pale and clammy skin, fast or weak pulse, nausea or vomiting, and fainting [8].
- Action: Move to a cooler location, lie down, loosen clothing, apply cool wet cloths to the body, sip water, and seek medical attention if symptoms worsen or last more than an hour. Avoid alcoholic and caffeinated beverages, as they can lead to further dehydration [8].
Heat Stroke
- Symptoms: High body temperature (above 103°F), hot, red, dry, or damp skin, rapid and strong pulse, headache, dizziness, nausea, confusion, and unconsciousness.
- Action: Call 911 immediately. Move the person to a cooler place, use cool cloths or a cool bath to lower body temperature, and do not give the person anything to drink. Heat stroke is a medical emergency and can be fatal if not treated promptly [9].
Special Considerations for Vulnerable Groups
- Children: Young children are more susceptible to heat-related illnesses because their bodies are not as efficient at regulating temperature. Ensure they stay hydrated, wear light clothing, and take frequent breaks from outdoor activities. Monitor them closely for signs of heat illness, especially when WBGT is high, and encourage indoor activities during peak heat hours [10].
- Elderly: Older adults may not adjust well to sudden temperature changes and are more likely to have chronic medical conditions that affect temperature regulation. Ensure they stay in cool environments, drink plenty of fluids, and limit strenuous activities during peak heat times. Checking in on elderly relatives or neighbors during heatwaves can help ensure their safety [11].
- Outdoor Workers: Those working outdoors in high temperatures need to take extra precautions. Employers should provide shaded or air-conditioned rest areas, schedule frequent breaks, supply plenty of water, and educate workers on the signs of heat illness. Workers should be encouraged to acclimatize gradually to the heat and wear appropriate protective clothing. Providing cooling vests and encouraging a buddy system where workers can monitor each other for signs of heat stress are additional preventive measures [12].
Tips for staying cool
- Stay Hydrated: Drink plenty of water throughout the day, even if you do not feel thirsty. Avoid beverages that can dehydrate you, such as alcohol and caffeine. In hot conditions, especially with high WBGT, it’s essential to replace electrolytes lost through sweating, so consider sports drinks or oral rehydration solutions [13].
- Wear Appropriate Clothing: Light-colored, loose-fitting clothing helps to keep you cool. Hats and sunglasses can provide additional protection from the sun. Moisture-wicking fabrics can help keep you dry and comfortable [14].
- Use Fans and Air Conditioners: Fans can help circulate air, and air conditioners can cool down your space effectively. If you don’t have access to an air conditioner, consider spending time in public places like libraries or shopping centers during the hottest parts of the day. Using fans in combination with an open window can help draw in cooler evening air [15].
- Limit Outdoor Activities: Try to stay indoors during peak heat hours (10 a.m. to 4 p.m.). If you must go outside, take frequent breaks and rest in the shade. Planning outdoor activities for the early morning or late evening can help reduce the risk of heat-related illnesses [16].
- Cool Down: Take cool showers or baths to lower your body temperature. Applying cool wet cloths to your wrists, neck, and forehead can also help. Staying indoors in air-conditioned environments during extreme heat can significantly reduce the risk of heat-related health issues [17].
Enhancing Indoor Air Quality During Summer
High outdoor temperatures and Wet Bulb Globe Temperatures can affect indoor air quality. Here are additional strategies to improve IAQ during the summer months:
- Seal Leaks: Ensure windows and doors are properly sealed to prevent outdoor pollutants from entering your home. Weatherstripping and caulking can help reduce infiltration [18].
- Use Exhaust Fans: In areas like kitchens and bathrooms, use exhaust fans to remove hot, humid air. This can help maintain a more comfortable indoor environment and improve air quality [19].
- Regular Maintenance: Clean and replace air filters in your HVAC system regularly to ensure it operates efficiently and effectively filters out pollutants. Dirty filters can reduce airflow and compromise air quality [20].
- Monitor Indoor Air Quality: The first step to monitoring indoor air quality is checking the outdoor air conditions at AirNow.gov [21]. Outdoor air can infiltrate and build up inside. You can also use an indoor air quality monitor [22] that measures particulate matter at different sizes, such as PM1, PM2.5 and PM10, as well as volatile organic compounds (VOCs) [23].
- Upgrade HVAC filters: Higher level MERV filters can reduce the amount of indoor air pollutants, from PM to VOC to viruses, in the air. According to the EPA [24]: “Many home HVAC systems will have a MERV-8 filter installed as the default. Upgrading to a MERV-13 rated filter, or the highest-rated filter that your HVAC system fan and filter slot can accommodate, could improve the system’s efficacy in removing viruses from circulated air. Before making any changes to the air filter in an HVAC system, users should consult their HVAC manual or an HVAC professional.”
- Use Portable Air Cleaners: You can use fan-and-filter air cleaners, such as the recently popularized DIY Corsi-Rosenthal Cube, and/or HEPA purifiers [25] to clean the indoor air from pollutants including pollen, mold, smoke, and viruses as well. Taking timely action to improve IAQ can reduce the negative effects of poor IAQ on your health.
Conclusion
As the sun sets on those blistering summer days, the air finally cools, offering a brief respite from the relentless heat. But the effects of extreme temperatures linger, not just in the warm asphalt or the still-humid air, but in the toll they take on our bodies and minds. The fatigue that sets in, the lingering headache, the way your heart seems to race just a bit faster—these are reminders that the heat isn’t just a passing discomfort; it’s a serious challenge that we must face with care and awareness.
At Air Support Project, we understand that each day of extreme heat is more than just another hot day. It’s a test of resilience, especially for those most vulnerable—children playing outside, elderly neighbors trying to stay cool in homes without air conditioning, outdoor workers pushing through their tasks despite the rising temperatures. These are the people who bear the brunt of the heat, who feel it in ways that numbers on a thermometer can’t fully convey.
Our goal is to help you navigate these extreme conditions with the knowledge and tools to stay safe. It’s about more than just surviving the heat—it’s about living through it with an awareness that protects your health and the health of those you care about. We want you to feel empowered to take action, whether that’s turning up the air conditioning, staying hydrated, or simply knowing when it’s time to take a break and cool down.
The heat is real, and so are its dangers. But with the right precautions and a clear understanding of how to manage these extreme conditions, you can keep yourself and your loved ones safe, even on the hottest days. Remember, taking care of yourself in the heat isn’t just about staying cool; it’s about respecting the power of nature and responding with the care that our bodies and minds deserve.
At Air Support Project, we believe in empowering communities with the knowledge and tools they need to maintain good air quality and health. As we learn how to take precautions against airborne health threats, let’s also learn what we can do to handle the heat safely. Wet Bulb Globe Temperature is a crucial factor in understanding heat stress and its potential health impacts. This measurement, which combines temperature, humidity, and other environmental factors, helps predict the risk of heat illness and guide effective heat safety measures [22]. By understanding and monitoring WBGT, we can take proactive steps to protect ourselves and our loved ones from the dangers of extreme heat. Stay cool, stay hydrated, and stay informed.
"Adopt the pace of nature: her secret is patience."
- National Weather Service. (n.d.). Heat index safety. Retrieved from https://www.weather.gov/safety/heat-index
- ClimateCheck. (2023). Understanding Wet Bulb Globe Temperature: The risks of high Wet Bulb Globe Temperatures explained. Retrieved from https://climatecheck.com/blog/understanding-wet-bulb-temperature-the-risks-of-high-wet-bulb-temperatures-explained
- Environmental Protection Agency. (2022, June 15). Ground level ozone basics. Retrieved from https://www.epa.gov/ground-level-ozone-pollution/ground-level-ozone-basics
- World Health Organization. (2021, September 22). Ambient (outdoor) air quality and health. Retrieved from https://www.who.int/news-room/fact-sheets/detail/ambient-(outdoor)-air-quality-and-health
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- Johns Hopkins Medicine. (2023). Heat-related illnesses: Heat cramps, heat exhaustion, heat stroke. Retrieved from https://www.hopkinsmedicine.org/health/conditions-and-diseases/heatrelated-illnesses-heat-cramps-heat-exhaustion-heat-stroke
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Download, Print, and Share
This infographic from the Air Support Project offers guidance on understanding Wet Bulb Globe Temperature (WBGT) and its impact on the body during outdoor activities. It includes suggested precautionary actions based on WBGT categories, helping you stay safe in hot weather. Ideal for use in military settings, sports, or any activity in direct sunlight. Click below to download your copy. Published under Creative Commons Attribution-NonCommercial-NoDerivatives License (http://creativecommons.org/licenses/by-nc-nd/4.0/ )
Sarah Masih, MD, MBA
Sarah Masih is the Executive Director of Air Support Project and has extensive experience in project management, fundraising, and communications. Her deep commitment to public health and her collaborative approach with community organizations and health experts make her a vital force in the fight for cleaner air and healthier communities.
SHEA O'NEIL
Volunteer
Creator of COVID-conscious advocacy works: writings, art, and social networking. BA degree in psychology, with over 11 years of continued education studies in allergy and autoimmune research, and continued research the past 3 years into airborne irritants and COVID-19. Parent, disabled rights advocate.
S. Riley
S. Riley is a mutlidisciplinary content creator and technology enthusiast with a background in crowdfunding and project management. He holds a BA in English, and is grateful to be able to utilize his unique skill set in service of Air Support Project's humanitarian mission.
Melissa Smallwood
Melissa Smallwood is Science and Technology Policy researcher with a background in neuroscience, psychology, and social science, and the author of The Future of Long COVID: A Threatcasting Approach. They are interested in how disability and healthcare justice intersect with emerging technologies, and are an advocate for COVID mitigation strategies to help end the pandemic.
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