Talk science with me! This will make you smile if you’re keen on talks about homeostasis, temperature regulation, and evaporation. Learn the signs/symptoms of various heat illnesses, including heat exhaustion and heatstroke.
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When spending time outdoors and exerting our bodies, it’s crucial to pay attention to heat-related illness signs and symptoms. The first line of defense against a heat-related illness such as heat cramps or heat strokes is prevention. Knowing the causes of heat illness can empower us to make better decisions in the backcountry to prevent this from becoming an issue.
Physiology of Our Body’s Temperature Management
Let’s geek out on science for a second here. We deserve it. Our bodies work 24/7 to maintain homeostasis – a balanced environment for all body systems and structures to function correctly to survive. To maintain homeostasis, our bodies constantly adapt to meet outside conditions. In hot and cold environments, our bodies must adapt to allow for organs to function well and for us to stay alive, which is somewhat important in the long run (*wink wink*). If we’re too cold, we begin shivering to heat our body. If we’re too hot, we sweat. Each of these adaptations are great but can have long-term costs to our homeostasis if we rely on shivering and sweating alone. Too much of a good thing can be a steep cost to homeostasis, just as too much ice cream may feel really good in the short term but may cause a belly ache later (especially if you forgot Lactaid at home and are lactose intolerant).
In various weather conditions, our circulatory system (i.e. heart and blood vessels, integumentary system (skin), and respiratory system (i.e. lungs) play the biggest roles in maintaining temperature homeostasis. Our vital organs can function between 97° to 100°F. If our body reaches the ungodly temperature of 107°F for a prolonged period, we are in big trouble and our vital organs may experience irreversible damage. This doesn’t mean you should check your temperature every 10 minutes outside, but it’s certainly something to keep in mind.
How Our Body Loses Heat
Our body can lose heat through evaporation, radiation, conduction, and convection. We rely on evaporation and radiation for most heat loss.
Sweating does not alone help to manage our temperature, but the evaporation of sweat off our skin acts to cool our body. Those beads of sweat that form get sucked into the atmosphere and our skin cools. Someone who has acclimated to heat can lose up to 2 liters per hour of sweat – that’s an entire soda bottle!
With increased heat, our body dilates blood vessels close to the skin so they are larger and can transport more blood. In regular conditions, our body sends about one-third to one-half a liter of blood per minute to the skin. When things get hot and steamy, our body can send up to FOUR LITERS of blood per minute to the skin. This is a majority of how our heat is lost when the air temperature is lower than skin temperature. Basic science says energy likes to move from high to low, so energy moves from warmer to cooler temperatures and our skin gives its heat to the environment as it warms up.
Risk Factors for Heat Illness
Our risk of getting heat illness changes based:
- Personal health
- Medication/alcohol use
- History of heat illness
- Basal metabolic rate, which depends on age, gender, and body composition/size. Our basal metabolic rate is our body’s furnace for burnin’ all the nutrients we take in. While our metabolism alone will not help regulate body temperature, nutrition plays an integral role in heat and cold related illnesses!
Heat Illness Signs and Symptoms
Dehydration is a beast that needs to be tamed to decrease the risk of heat-related illness, cold-related illness, and altitude illness. We lose water through sweating, urination, breathing, and (yes, we’re going here) diarrhea. Tips to prevent dehydration:
- Drink a cup of water 15 minutes before starting your activity
- Drink 1 to 1.5 cups (0.2 to 0.3 liters) of water every 20-30 minutes during activity
- Drink before you’re thirsty!
- Urine should be clear to pale yellow; dark urine may indicate dehydration
- To make drinking water easier, pack a hydration reservoir for easy sipping
- Set a timer on your watch for every 20 minutes to remind you to drink water
- Eat nutritious snacks to replace salt lost in your sweat
Fainting due to heat stress happens when blood begins pooling in large veins, such as those in our legs because of dilation of blood vessels. Treatment of fainting includes lying the individual flat and elevating legs above heart level. Signs and symptoms include:
- Tunnel vision
- Nausea, sweating, dizziness, weakness
- Sudden fainting
Ever go for a hike/run on a warm day and feel like the side of your abdomen or calf is squeezing? Yes, my friend, you’ve likely had a heat cramp! These are painful muscle contractions in hot conditions, but the cause is not entirely known. The important thing is to replace salt (sodium, potassium, and calcium) lost from sweating, as heat cramps can develop from electrolyte imbalance. To alleviate cramps, you can gently stretch (NOT massage!) the muscle cramp/spasm, plus take in some salt (half a teaspoon in a liter of fluid) + calcium (such as a Tum).
Our body works hard to maintain its preferred body temperature, which can fatigue our body from coping with the heat. Heat exhaustion is the tiredness alone, though dehydration can sometimes coexist with the fatigue. Signs and symptoms include:
- Elevated heart rate and respiratory rate
- Skin pale, cool, clammy
- Headache, nausea, weak, tired, dizzy
- Temperature normal or slightly higher
Heatstroke is no joke. Seriously. It is a life-threatening emergency and is a reason for evacuating from the backcountry environment to be evaluated by a licensed professional. An individual with heatstroke is no longer able to cool themselves. The onset can be pretty rapid and the major difference between heat exhaustion and heatstroke is the alertness of the individual. With heat stroke, the mental status changes. This means you or your partner may not be oriented to person (who they are), place (where they are), and/or time (of day/week/year). Signs and symptoms include:
- Elevated heart rate and respiratory rate
- Skin pale, *warm*, clammy
- Headache, weakness, seizures, decreased coordination
- Altered mental status** (confusion or uncooperativeness)
- Temperature >104°F (40°C)
How to Learn More
Did this topic interest you? I learned this information during my National Outdoor Leadership School (NOLS) Wilderness First Responder (WFR) course! I highly suggest you check out the NOLS Wilderness First Aid (WFA) or NOLS WFR (pronounced “woof-ehr”) course to further educate and empower yourself in the outdoors. This knowledge has helped me be more confident in the outdoors and during general emergent situations.
- We lose most of our body heat through evaporation (sweating) and radiation (increase blood flow to the skin).
- Risk of heat illness changes based on individual age, gender, body composition/size, health, medication/alcohol use, and history of heat illness.
- If you’re thirsty, you’re already dehydrated. Before beginning your outing, drink a cup of water 15 minutes before starting. Then, drink 1 to 1.5 cups (0.2 to 0.3 liters) of water every 20-30 minutes during activity.
- Heat cramps can begin with electrolyte imbalance and can be treated with gentle stretching and ingesting sodium/calcium.
- Heat syncope is fainting because of heat and could be treated by lying flat and elevating legs.
- Heat exhaustion is fatigue from the stress of dealing with heat and skin will be pale, cool, and clammy.
- Heatstroke is a life-threatening condition and will present differently than heat exhaustion by altered mental status. Someone with heat exhaustion should be evacuated from the backcountry environment.
- To learn more about wilderness medicine, I suggest you explore the NOLS (National Outdoor Leadership School) classes in Wilderness First Aid (WFA) and Wilderness First Responder (WFR).
- Learn more by reading the NOLS Wilderness Medicine book, 7th edition, from REI!
Mountaineers, T. (2016). Mountaineering: Freedom of the Hills (8th ed.). Mountaineers Books.
Schimelpfenig, T. (2016). NOLS Wilderness Medicine (6th ed.). Stackpole Books.
Feature Photo by Bluewater Sweden on Unsplash
Post Updated July 16, 2022