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Heat-related illnesses and dehydration - symptoms, preventions, and treatments for hikers

Updated: Dec 26, 2020

Heat-related illnesses and dehydration that happen during outdoor activities can be life-threatening. However, with a better understanding of your body and more preparation, heat injuries are preventable. Of course, we all want a happy and safe trip, so let's get prepared.

Physiology - our body temperature regulation:

When we exercise, our body temperature rises. The brain temperature regulator (hypothalamus) controls how our body reacts to heat. The heat is lost to the surrounding by three means:

  • Sweat evaporation: which is the most important mechanism. When our body temperature rises during exercise, we start sweating. Heat is lost to the surrounding when the sweat evaporates, causing the skin to cool. Blood vessels under the skin dilate, blood is carried to the skin, and is cooled.

  • The lungs

  • Conduction, convection, and radiation

Factors that make heat dissipation more difficult:

  • Strenuous exercise: more heat is produced

  • More fat: more heat is trapped due to a thicker insulating layer

  • Higher environment temperature: the body further heat up by the surrounding

  • Higher humidity: sweat cannot quickly evaporate

  • Dehydration: water loss from sweat and respiration is not replaced

Heat-related illnesses

Heat cramps - onset when the body dehydrates, large muscles, e.g., the leg and abdominal muscles cramp and sweating heavily than usual.

Heat fatigue - symptoms include rapidly tired and weak when exposed to abnormally high temperature or humidity. Recovery after exertion is slower than usual. Alerting and addressing the situation at this stage can prevent more severe problems.

Heat exhaustion - should be considered severe. Patients with heat exhaustion may present muscle cramping, fatigue, nausea, headache, dizziness, shallow+fast breathing, and rapid+weak pulse. Under heat exhaustion conditions, the skin can be cold and wet, with the body still functioning to remove heat. However, immediate actions have to be taken, or heat exhaustion can progress to heatstroke.

Heatstroke - condition deems to be severe and life-threatening. Symptoms included: high body temperature (greater than 39.4 degrees celsius), red/hot/dry skin; sweating may be impaired with body dysfunction to dissipate heat, headache, nausea, confusion, and unconsciousness.

Emergency medical attention is necessary as a very high body temperature can damage the brain and vital organs, leading to multiple organs failure, and death.

Mixed heat-injury syndromes - Sometimes, heat-injury patients may present mixed symptoms and signs in different levels of heat-related illnesses. It could be hard to distinguish one level from another. The difference is a matter of seriousness. It is more difficult to recover from heat exhaustion and heatstroke than heat cramps and fatigue. The idea is to act fast before things get worst.

9 Tips for heat injury preventions:

1. Fluid replacement: the most important way of preventing heat injury is drinking water. Also, you can intake sports drinks with electrolytes. General guidelines of fluid intake:

  • Pre-hydrated: 0.5 -1 liter 2 hrs before hiking

  • 1 liter per hour in a hot and humid day

  • Continue to replenish fluids (water and electrolytes) after hiking.

  • Drink before you are thirst; take small and frequently sips

  • Hourly fluid intake should not exceed 1.5 liters, and daily intake should not exceed 11 liters. Drinking too much water can lower blood sodium concentration to an abnormal level. You can avoid this by adding sports drinks or taking salty snacks when hiking on a hot and humid day.

  • Fluid needs depend on the weather, intensity of exercise, and individuals differences.

  • The U.S. Army Public Health Command has published a water consumption table recommended in different weather conditions and work-out intensity. Use it as guidelines and modify according to your need regarding local weather and individuals' health condition.

recommended water consumption by U.S. Army

2. Diet: contain fresh salads, fruits, and light salty food as they help replace many electrolytes.

3. Avoid the hottest period: start early in the day, avoid hot summer, and choose a route covered with shade.

4. Outfit: wear loose, lightweight, and light color clothing that allows heat dissipates and does not trap the heat

5. Protect yourself from the sun: wear sun-protection clothing, put on sunscreen, and wear a broad brim hat.

6. Monitor your urine - decrease pee frequency and dark color urine is a sign of dehydration; take prompt action to replenish water and electrolytes. You can follow the suggestion from the urine color chart below:

urine color chart to monitor dehydration

7. Take longer breaks and more frequently on hot and humid days.

8. Know yourself - build up hiking experience and monitor your body hydration condition under different weather conditions. Don't go on a significant hike in hot and humid weather without preparation.

9. Alcohol and medicine may disturb the heat-dissipating mechanism. Take extra caution if you are under medication and do not intake alcohol before and during hiking.

Treatments for heat injuries

Heat cramps and fatigue - slow down and remove yourself from exercise. Adequate fluids (water and *electrolytes) replacement, rest in a cool place, soak your hat and shirt with cool water. You can stretch your cramp muscles gently.

Heat exhaustion- remove yourself from exercise, stay in a cool place, drink cool water and *electrolytes, apply iced towels, or spray yourself with cold water. Suppose symptoms persist and you don't feel any better after an hour. In that case, you should seek medical treatment with more aggressive fluid replaced by intravenous fluids.

*electrolytes sports drink can enhance recovery; you can also intake dilute sports drink to prevent the stomach's discomfort

Heatstroke - transferred to the emergency room as soon as possible. Before the ambulance or first aid personnel arrive, you can do the following,

  • keep the patient away from the sun

  • remove most of his/her clothes

  • apply cold towels to the trunk, abdomen, and extremities,

  • apply cold towels/sponge/ice under armpit / inner thigh

  • fanning to stimulate airflow

  • maintain the airway


Dehydration shares similar symptoms as heat-related illnesses such as headache, dizziness, nausea, fatigue, and cramps. Therefore, apply the same techniques such as hydrating yourself, resting in a shaded area, and cool yourself with wet towels.

Knowing how to prevent heat-related illness benefits not only you but also your companion.

Friends of Polar Bear wish you a safe and happy outdoor trip.

For your fact check:

Reid, D.C.: Sports Injury Assessment and Rehabilitation. New York, Churchill Livingstone 1992, p.477-482.

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