Estimated reading time: 12 minutes
Summer heat is one of the main environmental sources of injury, illness and death. And as the global average temperature and extreme summer heat rise every year, more people will be affected worldwide by extreme heat every year.
This post is a shorter version of the original post, Climate Change, Deadly Heat and You, so if you want to take a deeper dive into the science of extreme heat check out that post.
To start off, here's a graphic I made recently of increasing temperatures in Houston, Texas over the past 125+ years. What's important about this graphic is what comes with it, warmer average temps mean hotter heat waves.
It's not just the high temperature of a heat wave that kills, it's the nighttime highs. Warmer nights keep people from recovering from the heat, and put them at a worse position to cope with the heat the next day.
The main source of heat is the sun. Solar radiation reflects off the ground, is also absorbed by the ground, then re-radiated back into the air. The balance between the environment and heat retained by your body is shown in the picture below.
In summary, a hot environment adds heat to your body, while evaporation of sweat takes heat away. (In extreme cold, this operates in reverse! Radiation, conduction and convection remove heat from your body.)
Evaporation of sweat is the second most effective way your body cools itself-- the most effective way to cool yourself is by behavior, or the things you do to keep yourself cool.
Your body wants to run at an even temperature, not too hot, not too cold, usually around 37C / 98F. The part of your brain called the hypothalamus monitors your body temperature, and when it gets too hot, it sends a signal to your sweat glands to start sweating.
As your skin sweats, the sweat evaporates off your body. When the sweat on your skin evaporates, it requires energy to change from a liquid into a vapor. The energy that drives that change is the heat from your body. Thus energy is taken out of your body and you are cooled. Of course, the higher the humidity, the less effective this mechanism works.
The figure below is a great conceptual drawing that shows the combined effect of evaporation and convection. Heat is taken out of your body by evaporation, and a breeze, further enhancing your cooling by convection, carries the warm vapor away.
When it’s very hot outside, or very humid, or you are working hard, or you can’t sweat for some reason, then evaporation is less effective, and your internal body temperature starts to rise. This eventually leads to hyperthermia and heat illness.
Let me repeat the most important concept -- The MOST effective way to cool yourself is by behavior - doing the things that help keep you cool. Things like drinking cold water, turning on a fan, going into an air-conditioned space on a hot day, and so forth. Hard to put that into an equation. :)
The health effects of heat fall in a range from minor symptoms to life threatening illness. Any of these conditions could be caused by extreme exertion, but they are all made much worse by hot, humid weather.
The table below summarizes the range of heat illness. The basic treatment for all of these is rapid cooling by whatever means possible, from going inside, to cool drinks, to draping with cold wet cloths, to ice packs in key places, to immersion in ice water.
Please note, medical information shown in this article is for illustrative purposes only and does not constitute medical advice to the reader. Please ask your doctor or other health professional if you have further questions.
Spectrum of Heat Illnesses*
ProblemSigns & SymptomsCauseTreatmentHeat CrampsMuscle cramps with exertionDehydration caused by exercise, heat, or bothStretching, rehydration, rest
Ease back into activityExercise Associated CollapseWarm skin
Sweaty
Low blood pressure
Fainting at the end of a period of strenuous exerciseWhen you stop exercising your heart slows down
Blood vessels are still dilated so your blood pressure drops
Blood flow to brain drops
Leading to fainting
Quick recoveryMake sure it’s not something else! (e.g. stroke, heart attack, etc.)
Shade, rest, cold water
Recovery should be rapid, if not then transport to hospitalHeat Exhaustion
/ Heat InjuryWeakness
Warm to hot skin, but can also be cool and clammy
Profuse sweating
Rapid heart beat (>100)
Elevated core temperature (38.3 – 40C /101 – 104F)**
NOT confused or deliriousDehydration and elevated core temperature result in weakness and rapid heart beat
Eventual decreased blood flow to kidneys and other organs may cause damageRapid cooling
Go to the hospital,
especially if prolonged or extreme episodeHeat StrokeHot, flushed/red, skin that is usually dry
IS confused, stumbling, dizzy, delirious
Core temperature >=40.5C/105F**
Altered mental status
Unconsciousness
Pending deathAs above, and...
Prolonged reduced blood flow to brain and vital organs leading to deathA life-threatening emergency!
Ambulance to the nearest hospital
Start cooling immediately while waiting for ambulance* O’Conner, et al., Exertional heat illness in adolescents and adults: Epidemiology, thermoregulation, risk factors and diagnosis, in UpToDate.com, last updated May 13, 2026.
** Core temperature is measured by rectal thermometer. Other methods will read about a degree or more cooler than true temp
First Aid for Heat Exposure
The most important and obvious thing to do for someone who is suffering from extreme heat is to COOL THEM OFF! Here are some techniques to accomplish that...
Stopping all activity and resting
Siting or laying in the shade, or going inside
Drinking cold, water or better yet, diluted sports drink (a little sugar helps them to absorb the water into their bloodstream -- in other words, it helps them to hydrate!)
Cold water spray and fans (Note: This may not work in very hot and/or humid environments!)
Putting ice packs on the neck, arm pits and groin (all the places where blood flow is the highest)
Draping them in cold, ice water-soaked towels and sheets
Immersing in cold water or ice water
(Immersion requires at least two people to monitor the victim, one to keep them from going underwater should they lose consciousness, and the other to check vital signs and do other tasks)
If the heat illness is serious you should call for an ambulance while you are cooling them down. If you are in a remote area or are unable to get an ambulance for whatever reason, stop cooling when they start shivering, or after about 15 – 20 minutes of aggressive cooling. Ideally you would stop cooling them when their rectal temperature drops to 38C / 101F.
Some important points to remember about heat illness…
You can’t always tell how bad it is just by looking at someone
Call for an ambulance early or take them to the hospital if you are concerned
The longer a person’s core temperature is elevated, the worse the outcome
Rapid cooling is the cornerstone of treatment
Protect Yourself from Extreme Heat
Government action is important to protect society as a whole, and to protect those who are more vulnerable. But society's preparedness also rests on you, the individual. There is plenty you can do to protect yourself and your family. And remember, your behavior is the number one method for protecting yourself from extreme heat.
Protecting yourself from extreme heat starts with changing your behavior during heat waves, and may eventually involve moving to a cooler climate. The measures you take will differ depending on your personal risk factors and your available resources.
Some steps to take to prepare for a heat wave or even just hotter summer months...
Stay hydrated by drinking plenty of water, even if you don't feel thirsty
Seek air-conditioned spaces during the hottest parts of the day
Wear light, loose-fitting clothing and a hat when outdoors. Sunscreen does NOT protect you from the heat, it only protects exposed skin from sun damage. I like sun shirts from Huk! (Not an affiliate link, just great sun clothes I wear almost every day.)
Avoid strenuous activity during peak heat hours
Check on vulnerable friends, family, and neighbors during heat waves (the elderly, people living alone, people with chronic disease, etc.)
Learn the signs of heat illness and how to respond (from above!)
Some things you may do over the long term...
install heavy curtains or reflective film over windows that get a lot of sun. Rejecting sun light and heat is super helpful to keep inside temps down
make sure your air conditioner is in good working order, whether a window unit or central air for your house
tighten up gaps that leak air in your house, otherwise you are working to cool the air outside!
make sure your refrigerator is in good condition. clean the coils, make sure air can circulate around it
have backup power to run fans, window air-conditioners, or your whole house A/C, and your fridge
make a "climate safe" room in your house. this is one room that is better insulated than other parts of your house or apartment
make a personal "heat wave plan". I just thought this up. If people can have a plan for other disasters, why not for a heat wave?!
have an emergency fund of money - get your finances in order. Haven't talked about his in a long time, but it's super important!
start thinking about eventually moving or retiring North
As our climate continues to warm, we must consider heat waves a major threat to our health and homes. By understanding the risks, taking personal precautions, and supporting community-wide adaptations, we can reduce the impact of extreme heat on our wellbeing.
Do you have any ideas about how to beat the heat? Put them in the comments below. Thank you.
Stay cool, stay safe, and remember: we're all in this together as we face the challenges of a warming world.
Source: Surviving Deadly Heat
