Emergency heat safety

Heat-related illness is one of the most preventable medical emergencies, and also one of the most commonly misunderstood. The line between “I feel hot” and “this is a medical emergency” is thinner than most people realize, and the difference comes down to recognizing specific symptoms and acting on them quickly.

In our full investigation into staying cool without AC, we covered strategies for managing heat at home. This article covers what happens when those strategies aren’t enough — how to recognize the stages of heat illness, what first aid actually works, and when to call 911.

The Problem

Heat is the deadliest weather-related hazard in the United States. According to the CDC, extreme heat kills more Americans each year than hurricanes, tornadoes, and floods combined (CDC: About Heat and Your Health). The National Weather Service reports that heat has been the leading cause of weather-related deaths in most years for the past three decades, exceeding the combined toll of all other severe weather events (NWS: Heat Safety).

Part of the problem is that heat illness is insidious. It doesn’t arrive with sirens or a visible wall of water. It develops gradually — a headache here, some dizziness there — and by the time the warning signs are unmistakable, the person may already be in danger. Many people don’t recognize the warning signs until it’s too late, because the symptoms (nausea, headache, fatigue) feel like a dozen other things.

The other part of the problem is that the body’s cooling system has real limits. Sweating works by transferring heat from your body into water on your skin, which then evaporates. When the air is hot and humid, that evaporation slows or stops entirely. The National Weather Service heat index chart shows that at 90°F with 60% humidity, the “feels like” temperature is 100°F. At 95°F with 70% humidity, it’s 124°F — the danger zone for heat stroke even for healthy people doing nothing strenuous (NWS: Heat Index).

Who’s at Risk

Anyone can develop heat illness, but some groups are significantly more vulnerable. The CDC identifies the following high-risk groups (CDC: Heat and People at Increased Risk):

Older adults (65+). The body’s ability to regulate temperature declines with age. Older adults produce less sweat, have reduced cardiovascular response to heat stress, and are more likely to be taking medications that impair heat tolerance. The thirst mechanism also weakens with age — older people are less likely to feel thirsty even when dehydrated (CDC: Heat and Older Adults).

Infants and young children. Children’s bodies heat up three to five times faster than adults’ because they have a higher surface-area-to-body-mass ratio and their sweat glands are not fully developed. They also depend on adults to recognize when they’re overheating and to move them to a cooler environment.

Pregnant women. Pregnancy increases metabolic heat production by about 20%. Dehydration during pregnancy can also affect amniotic fluid levels and fetal heart rate. The CDC includes pregnant women in its high-risk categories for heat-related illness.

People with chronic conditions. Heart disease, diabetes, obesity, high blood pressure, kidney disease, and respiratory conditions all impair the body’s ability to handle heat stress. Diabetes can damage nerves and blood vessels that affect sweat glands. Heart disease limits the cardiovascular system’s ability to increase blood flow to the skin for cooling.

Outdoor workers. Construction workers, agricultural workers, landscapers, delivery drivers, and roofers are at elevated risk because they’re physically active during the hottest part of the day, often in direct sun. OSHA’s heat safety standard emphasizes that employers must provide water, rest, and shade when the heat index exceeds 80°F (OSHA: Heat Safety).

People without air conditioning. Homes without AC can reach dangerous internal temperatures — especially on upper floors and in rooms with west-facing windows. The CDC recommends spending at least 2 hours per day in an air-conditioned space during extreme heat events, even for people who don’t feel sick (CDC: Heat and People without AC).

People on certain medications. Several common medication classes impair heat tolerance — antihistamines, beta-blockers, diuretics, antidepressants, and stimulants. See the medication section below for details.

Heat Exhaustion vs Heat Stroke

The two conditions are stages on the same spectrum, but they require fundamentally different responses. Heat exhaustion is serious and needs treatment. Heat stroke is a medical emergency and needs an ambulance.

Source: National Weather Service. The NWS notes that heat stroke occurs when the body’s temperature regulation fails and body temperature rises to 104°F or higher, causing the brain and other organs to begin suffering damage (NWS: Heat Related Illnesses).

The key distinction to remember: heat exhaustion involves heavy sweating and normal mental function. Heat stroke involves altered consciousness and skin that is hot and dry because the body has stopped sweating. If a person is confused, unconscious, or has stopped sweating despite being obviously overheated, that is heat stroke until proven otherwise.

Prevention

Heat illness is almost entirely preventable with the right habits. The strategies below are drawn from CDC and NWS guidance.

Hydration schedule

Don’t wait until you’re thirsty to drink water. Thirst is a lagging indicator — by the time you feel it, you’re already dehydrated. The CDC recommends drinking more water than usual during hot weather, regardless of your activity level (CDC: Tips for Preventing Heat-Related Illness). A practical schedule:

• Before going out: Drink 16–24 oz of water 30–60 minutes before outdoor activity.
• During activity: Drink 8 oz every 20–30 minutes when working or exercising in the heat.
• After: Continue hydrating until urine is light yellow or clear.

Electrolyte balance

If you’re sweating heavily for more than an hour, you’re losing more than water — you’re losing sodium, potassium, and chloride. Replacing water without electrolytes can cause hyponatremia (low blood sodium), which has symptoms that mimic heat exhaustion (nausea, headache, confusion). The CDC recommends electrolyte-replacement drinks or salty snacks alongside water for prolonged sweating. Sports drinks, oral rehydration solutions, or even a light snack with salt can maintain electrolyte balance.

Clothing

Light-colored, loose-fitting, lightweight clothing allows sweat to evaporate and reflects solar radiation. Dark colors absorb heat. Synthetic fabrics that don’t breathe (polyester, nylon) trap heat against the skin. Cotton, linen, and bamboo are better choices for hot weather. The CDC’s extreme heat guidance notes that wearing appropriate clothing reduces heat stress (CDC: Extreme Heat Tips).

Timing outdoor activity

Schedule outdoor work and exercise for the coolest parts of the day — early morning before 10 AM or evening after 6 PM. The hottest hours are 1–6 PM, when solar radiation is most direct. The NWS recommends that during heat advisories, strenuous outdoor activity be limited to the morning and evening, with frequent rest breaks in the shade or air conditioning (NWS: During a Heat Wave).

Acclimatization

Your body adapts to heat, but it takes time. Full heat acclimatization takes 7 to 14 days of gradually increasing exposure. During this period, the body learns to sweat earlier and more efficiently, increase blood flow to the skin, and retain electrolytes (CDC: NIOSH Heat Stress — Acclimatization). Outdoor workers and athletes returning to hot weather after a cool spell need a graduated schedule: start with 20% exposure on day one and increase by 20% per day.

The buddy system

Heat illness impairs judgment. A person developing heat stroke may not realize anything is wrong — confusion is one of the first symptoms. The buddy system (checking on each other regularly) is standard practice in military and industrial settings for exactly this reason. At home, check on elderly neighbors, family members who live alone, and anyone without AC during a heat wave. The CDC specifically recommends checking on at-risk people at least twice a day (CDC: About Heat and Your Health).

First Aid for Heat Exhaustion

Heat exhaustion is the body’s response to excessive water and salt loss through sweating. It is not immediately life-threatening, but it can progress to heat stroke if left untreated. Take these steps immediately:

1. Move to a cool place. Get the person out of the sun and into the shade, an air-conditioned room, or at least a well-ventilated area. If indoors is not accessible, find the shadiest spot available.

2. Cool the body. Apply cool, wet cloths to the skin. If possible, have the person sit in a cool bath or shower. Alternatively, spray or sponge cool water on the skin and use a fan to accelerate evaporative cooling. Apply ice packs or cold compresses to pulse points — neck, armpits, wrists, and groin — where major blood vessels are close to the skin surface. The Mayo Clinic recommends this pulse-point cooling approach as an effective way to lower core temperature (Mayo Clinic: Heat Exhaustion First Aid).

3. Hydrate. Have the person sip cool water slowly. Do not let them gulp — drinking too quickly can cause nausea and vomiting, which worsens dehydration. If the person complains of nausea, stop giving water. Sports drinks or oral rehydration solutions are preferable to plain water if available, as they replace lost electrolytes.

4. Remove excess clothing. Loosen or remove any tight, heavy, or unnecessary clothing. Shoes and socks should come off. Remove jewelry or accessories that may restrict circulation as the body swells.

5. Rest. The person should rest lying down in the cool environment for at least 30–60 minutes. Do not let them return to activity or heat exposure until symptoms have fully resolved.

When to seek medical help: If symptoms worsen despite treatment, if the person can’t keep water down due to vomiting, if symptoms persist for more than one hour, or if the person’s temperature continues to rise above 101°F despite cooling efforts — call a doctor or seek medical attention. Heat exhaustion that doesn’t improve can progress to heat stroke.

First Aid for Heat Stroke

CALL 911 IMMEDIATELY. Heat stroke is a life-threatening medical emergency. Do not wait. Do not “wait and see.” Every minute of delay reduces the chance of survival.

While waiting for emergency services:

1. Move to a cool area. Get the person out of direct sun. If possible, move them to an air-conditioned space. If not, move them to the shadiest, best-ventilated spot available.

2. Remove clothing. Take off as much clothing as possible, especially outer layers. This maximizes skin exposure for cooling.

3. Cool the body aggressively. This is the single most important thing you can do while waiting for paramedics:

• Immerse the person in cold water if possible (a bathtub, a large basin, a kiddie pool, a lake). Cold water immersion is the gold standard for heat stroke treatment — it cools the body 25–30 times faster than passive cooling (CDC: NIOSH Heat Stress — First Aid).
• If immersion is not possible, apply ice packs or cold packs to the neck, armpits, and groin. Cover the body with cold, wet sheets or towels and replace them frequently as they warm up.
• Spray or pour cold water over the person’s body while fanning them vigorously. Evaporation is the body’s native cooling mechanism — you’re accelerating it.

The goal is to bring core body temperature below 104°F as quickly as possible. The NWS emphasizes that cooling treatments must begin immediately — do not delay cooling while waiting for paramedics (NWS: Heat Related Illnesses).

4. Do NOT give fluids. If the person is confused, unconscious, or has an altered mental state (all common in heat stroke), they cannot safely swallow. Giving water to a person who cannot swallow properly can cause choking, vomiting, and aspiration. Paramedics will administer IV fluids if needed. Do not attempt oral rehydration during heat stroke.

5. Monitor breathing and consciousness. Stay with the person until help arrives. If they become unconscious, place them on their side (recovery position) to keep the airway clear. Be prepared to perform CPR if breathing stops.

Heat stroke mortality

Heat stroke has a mortality rate of 10–50% depending on the patient’s age, underlying health conditions, and how quickly treatment is initiated (CDC: Heat Stress Symptoms). The most important variable is time: patients who receive aggressive cooling within 30 minutes of onset have significantly better outcomes than those who don’t. This is why the first-aid instruction is “cool immediately, not after waiting.”

Kids and Hot Cars

A car parked in the sun heats up much faster than most people realize. On a 90°F day, the interior of a parked car can reach 109°F in 10 minutes and 125°F in 20 minutes. Cracking the windows makes almost no difference — research by the National Weather Service and the San Jose State University Department of Meteorology found that rolling down windows 2 inches had little effect on the rate of interior heating (NWS: Children, Pets and Vehicles; Noaa.gov: Heat and Cars).

A child’s body temperature rises three to five times faster than an adult’s. When a child is left in a hot car, their core temperature can reach lethal levels in as little as 10–15 minutes. Since 1998, more than 970 children have died in the United States from vehicular heat stroke. According to data from the National Safety Council, over half of these deaths occurred because a caregiver forgot the child in the car.

The rule is absolute: never leave a child in a parked car, even for “just a minute.” This includes running into a store, dropping off a package, or any other quick errand. It includes cars parked in the shade. It includes cars with the windows cracked. It includes cars with the air conditioning running (the AC can fail or the car can turn off). The CDC is explicit on this point: “Never leave infants, children, or pets in a parked car, even if the windows are cracked” (CDC: Preventing Heat-Related Illness).

The same rule applies to pets and to adults with disabilities or limited mobility who cannot exit a vehicle on their own.

Medication Interactions

Several common classes of medication impair the body’s ability to handle heat. If you or someone you care for takes any of these medications, the CDC recommends consulting a doctor during heat waves about specific precautions (CDC: About Heat and Your Health).

Antihistamines (cetirizine/Zyrtec, loratadine/Claritin, diphenhydramine/Benadryl)

Antihistamines suppress the body’s histamine response — but they also suppress sweating by blocking the muscarinic receptors that activate sweat glands. Reduced sweating means reduced evaporative cooling. Diphenhydramine (Benadryl) has the strongest anticholinergic effect and the greatest impact on heat tolerance. This is why the NWS and CDC warn that allergy medications can increase heat sensitivity (NWS: Heat Illness).

Beta-blockers (metoprolol, atenolol, propranolol)

Beta-blockers reduce heart rate and cardiac output. Since the body relies on increased cardiac output to move blood to the skin for cooling, beta-blockers limit the cardiovascular system’s ability to respond to heat stress. People on beta-blockers may not feel as hot as they actually are because the medication blunts the heart-rate response that normally signals overexertion.

Diuretics (“water pills” — furosemide, hydrochlorothiazide, spironolactone)

Diuretics increase urine production, which accelerates fluid loss. In hot conditions where sweating already causes fluid loss, diuretics compound the dehydration risk. Electrolyte imbalances (especially low potassium) from diuretic use can also affect the heart’s electrical system under heat stress.

Antidepressants (SSRIs, SNRIs, TCAs, MAOIs)

Many antidepressants affect the body’s temperature regulation center in the hypothalamus. SSRIs and SNRIs (fluoxetine/Prozac, sertraline/Zoloft, venlafaxine/Effexor) can impair sweating and temperature regulation. Tricyclic antidepressants (amitriptyline, nortriptyline) have strong anticholinergic effects that block sweating. MAOIs can cause potentially dangerous interactions with heat.

Stimulants (amphetamine/Adderall, methylphenidate/Ritalin, other ADHD medications)

Stimulants increase metabolic rate and heat production. They also suppress appetite and thirst, which can lead to inadequate fluid intake. People on stimulant medications for ADHD may need to pay extra attention to hydration and rest breaks during heat waves.

What to do

• Do not stop or change medications without consulting your doctor. The risks of stopping blood pressure or psychiatric medications are generally greater than the risks of heat exposure with proper precautions.
• Talk to your doctor before a heat wave about specific risks and any dose adjustments that might be appropriate for the duration.
• Pay extra attention to hydration, rest breaks, and early symptom recognition if you take any of these medications.
• Know that the medication may mask symptoms — beta-blockers blunt the racing heart that normally signals overexertion, and antihistamines may reduce awareness of sweating.

External Resources

The following sources were consulted in researching this article. These are the authoritative references for heat-related illness recognition, first aid, and prevention.

• CDC: About Heat and Your Health — Primary US public health source on heat-related illness, prevention, risk factors, and medication interactions.
  https://www.cdc.gov/heat-health/about/index.html

• CDC: Heat and People at Increased Risk — Detailed risk factors for heat illness by age, health status, and socioeconomic factors.
  https://www.cdc.gov/heat-health/risk-factors/index.html

• CDC: Heat and Older Adults — Specific guidance for people 65+, including medication risks and the diminished thirst mechanism.
  https://www.cdc.gov/aging/emergency-preparedness/heat-stroke.html

• CDC: Tips for Preventing Heat-Related Illness — Top-line prevention recommendations including hydration, clothing, and never leaving people in parked cars.
  https://www.cdc.gov/disasters/extremeheat/heattips.html

• CDC: NIOSH Heat Stress — First Aid — Occupational first aid guidance for heat stroke and heat exhaustion, including cold water immersion protocols.
  https://www.cdc.gov/niosh/topics/heatstress/firstaid.html

• CDC: NIOSH Heat Stress — Acclimatization — Guidance on the 7–14 day heat acclimatization process for workers and athletes.
  https://www.cdc.gov/niosh/topics/heatstress/acclim.html

• NWS: Heat Related Illnesses — Official NWS guide to heat cramps, heat exhaustion, and heat stroke symptoms and first aid.
  https://www.weather.gov/safety/heat-illness

• NWS: Heat Index — The heat index chart and calculator for understanding “feels like” temperature and heat risk levels.
  https://www.weather.gov/safety/heat-index

• NWS: Children, Pets and Vehicles — Vehicle heating rate data and heat stroke risk for children left in cars.
  https://www.weather.gov/safety/heat-children-pets

• NWS: Heat Safety — Central NWS hub for all heat safety resources.
  https://www.weather.gov/safety/heat

• OSHA: Heat Safety — Occupational heat exposure standards, employer responsibilities, and worker safety guidance.
  https://www.osha.gov/heat-exposure

• EPA: Heat Island Impacts — How the built environment increases temperatures in cities and what communities can do.
  https://www.epa.gov/heatislands/heat-island-impacts

• NOAA: Heat Safety — Educational resources on heat safety from the National Oceanic and Atmospheric Administration.
  https://www.noaa.gov/education/resource-collections/safety/heat-safety

• Mayo Clinic: Heat Exhaustion First Aid — Clinical first aid guidance for heat exhaustion, including pulse-point cooling technique.
  https://www.mayoclinic.org/first-aid/first-aid-heat-exhaustion/basics/art-20056655

• Heat.gov — National integrated heat health information system portal from NOAA, CDC, EPA, and other federal partners.
  https://heat.gov/heat-safety/

• Heat.gov: Extreme Heat Tips — Combined extreme heat guidance from multiple federal agencies.
  https://heat.gov/data-tools/extreme-heat-tips-information-and-resources-cdc/