Heat illness can come from exposure to high temperatures, with or without over-exertion. Symptoms range from mild headaches to debilitating nausea and cramps, to briefly passing out, to a persistent altered level of consciousness, seizures, coma, or even death.
Heat illness can strike quickly and get in the way of a hike or other outdoor activities. Left untreated, heat illness can have dangerous consequences with long recovery times.
It’s important to pack and plan accordingly to prevent heat illness. Once outside, pay close attention to your body and make smart choices to keep your adventure going!
Symptoms and Description
Heat illness can come from both passive exposure to high ambient temperatures and exertion in the heat. This is because heat is gained both externally through your environment and generated internally by your body through exercise.
Proper hydration is essential for preventing and managing heat illness. Heat causes sweating, which draws fluid from your body. Your brain reacts by increasing your sensation of thirst. However, drinking too many fluids (overhydration) can be as dangerous or more so than dehydration. (see hyponatremia)
Humid conditions also increase susceptibility to heat illness. Sweat cools you off as it evaporates from your skin, but moisture in the air can significantly hinder that evaporative process. This is why humid environments can feel hotter than they actually are. 100 ºF (37.8 ºC) at 60% humidity will feel like 129 ºF (54ºC)! This perceived temperature is called the “heat index” and can be found in many weather apps.
Pay close attention to your body during hot temperatures or strenuous activity, especially if you are not accustomed to exercise in the heat. Many symptoms of heat illness (like nausea or dizziness) can be easily mistaken for other conditions. Also pay attention to the amount of water or sports drink you consume, as this can give clues to the problem.
Symptoms
- Dizziness
- Fainting
- Exhaustion
- Nausea
- Vomiting
- Muscle Cramps
- Headache
- Thirst
Are you or a companion experiencing any symptoms consistent with heat illness?
If yes, launch medical assessment below.
Defining Your Risk Category
Your risk of heat illness is based on environment, activity, and other personal health factors. Consider the following to define your risk category and plan accordingly.
Higher Risk
- The extremes of age (young children and elderly).
- People with sunburns may have impaired sweating, which reduces the body’s ability to shed heat.
- People who have suffered heat stroke are at greater risk for subsequent heat illness for months after the initial event.
- People on prescription drugs, which can either increase heat production or compromise the parts of the brain that regulate the body’s temperature (especially for the heart, high blood pressure, and mood). Anyone on prescription drugs should check with their doctor before undertaking new exertional activities in very hot conditions.
- People participating in intense physical activity in hot conditions.
- People in higher humidity environments.
- People wearing clothing or equipment which may limit the body’s ability to cool down. Work uniforms, denim, thicker non-breathable clothing can all increase the risk of heat illness.
- People drinking too many fluids (1L per hour or more) which increases risk for overhydration (see hyponatremia). Higher temperatures and prolonged exertion also increase the risk of hyponatremia.
- People who are unused to exercise in hot conditions.
- People consuming alcohol or stimulant drugs.
Guidelines for Safe Travel
Acclimate (condition) your body in advance
- You can improve your body’s ability to tolerate heat by heat acclimatization—Don’t go “cold turkey!” Prepare your body by exerting yourself for 1-2 hours a day in hot conditions for 10-14 days leading up to your adventure. This conditioning will improve your body’s ability to tolerate and shed heat, and the benefits can last for several weeks!
- If you are preparing for new activities (like long or steep hikes), realize that there are both small and large muscles that need to be specifically trained. Proper conditioning will help you have a safe and enjoyable adventure. Whenever possible, train your body with exercises that most resemble your planned activities. Hiking in is optional, hiking out is mandatory!
Hydrate
Dehydration can increase fatigue, increase level of perceived exertion, and increase core temperatures. All this leads to worsened ability to tolerate heat. Keep in mind that over-hydration can be as dangerous as dehydration (see hyponatremia). Awareness of risks and symptoms for you and your group is the best prevention.
- Always pack enough water to drink comfortably.
- Plan how to refill and purify water as needed throughout your adventure.
- Start your outing well-hydrated.
- Drink when you are thirsty, not to a specified plan. Drinking too much can be more dangerous than not drinking enough. Try not to drink more than 1L/hr of water or sports drink. (see hyponatremia)
- Pack salty foods and snacks to help prevent and treat hyponatremia.
- Certain medications can decrease the body’s ability to cool in the heat. Check with your doctor if on cardiac medicines, high blood pressure medicines, anti-anxiety/depressants, or stimulants.
- Alcohol and stimulant drugs also interfere with your body’s cooling ability and should be avoided in high heat.
- PACKING LIST: Water bottles, water filtration system, salty snacks
Protect against sun exposure
- Wear clothing that is breathable, lighter color to absorb less solar radiation, and lighter in weight while out in the heat. Large hats that provide shade to the front and back of the head will decrease heat gained from the sun.
- Bring portable shelter if none is available at your destination. Umbrellas and sunshades are especially important for beaches and sand dunes. Plan ahead!
- People with sunburns may have impaired sweating, which increases the risk of heat illness. Pack and apply sunscreen as directed.
- Sunscreen needs to be reapplied every few hours, more frequently with swimming and heavy sweating.
- PACKING LIST: Breathable light clothing, hats, portable shade, sunscreen
Passing Out in the Heat
Dizziness or passing out in the heat is usually due to the heat-induced swelling of blood vessels in the skin, pooling of blood in the lower extremities, and diminished return of oxygenated blood to the brain. This effect typically passes quickly with return to normal responsiveness. If someone passes out in the heat, consider the following factors and act accordingly.
Passing out may be due to hot temperatures or it could be due to an underlying medical condition. Especially if the person has medical problems, has chest pain or shortness of breath, or is pregnant, you should seek medical attention.
Collapse after prolonged exertion may often be due to changes in blood flow from the lower part of the body, not necessarily from the heat or medical conditions. If the person is otherwise comfortable and you don’t suspect a medical emergency, lay them flat in the shade to help them to fully recover.
Consider the risk and consequences of passing out again: Will the person have assistance? Will there be exposed terrain where the person could fall? Will there be shade and opportunity to rest?
If there are no other factors like medical problems or intense exertion, heat is the most likely cause of illness. Loss of consciousness demonstrates that a person is poorly acclimatized to the hot conditions. If this is the case, rest alone may not be enough.
Treatment Options
- Especially if the person has medical problems, has chest pain or shortness of breath, or is pregnant, you should seek medical attention.
- If the person is otherwise comfortable and you don’t suspect a medical emergency, lay them flat in the shade to help them to fully recover.
- Before continuing an activity or exercise in the heat, ensure that the person is able to eat, drink, and exert themselves comfortably.
- If the person has returned to feeling normal, continue on with your activity only if you feel you can do it safely.
Are you or a companion experiencing any symptoms consistent with heat illness?
If yes, launch medical assessment below.
Heat Rash
Heat rash (also known as prickly heat or miliaria) is a rash marked by clear fluid filled blisters, red bumps, and often an irritating itchy sensation. This is more commonly found in infants and younger children on the neck, chest, armpits, elbow creases, and groin, but it can also be seen in adults where clothes or skin folds cause friction.
While uncomfortable, this is not a dangerous rash. This is more common in hot and humid conditions, where people are sweating heavily and overheating. Heat rash develops from blocked sweat ducts, so perspiration becomes trapped in the superficial layers of the skin and causes local reactions and inflammation.
While usually self-limited, persistent rash with increased redness, pain, or swelling may represent a bacterial infection. (see rashes)
Treatment Options
Relieve symptoms by cooling the skin with cold water immersion or soaked cloth.
Heat Exhaustion
Heat exhaustion encompasses a wide variety of symptoms that can range from mild and uncomfortable to debilitating. The ability to treat and recover from heat exhaustion dictates the level of severity.
Symptoms may include dizziness, nausea and vomiting, muscle cramps, headache, and thirst. Thirst is usually a predominant feature of heat exhaustion and dehydration.
The amount of recent water intake can help differentiate from low salt levels causing similar symptoms. Lots of water or sports drinks (more than 1 L / hour) makes someone more likely to be overhydrated and hyponatremic, even if drinks contain electrolytes. (see hyponatremia)
Are you or a companion experiencing any symptoms consistent with heat exhaustion?
If yes, launch medical assessment below.
Heat Stroke
Heat stroke occurs with elevated temperatures and altered level of responsiveness. This may present as confusion, unresponsiveness, seizures, or a coma. It can come from exerting oneself, or simply from spending time in hot environments. The care is the same regardless of the cause.
Heat stroke often comes on gradually from a state of heat exhaustion that may be under-treated or unrecognized, but in some instances, it can occur rapidly. Intense physical activity (with greater metabolic heat generation) can rapidly increase the body’s temperature and can lead to a sudden and catastrophic event.
Heat stroke may appear with either sweaty or dry skin. The skin may be flushed or often pale.
Anyone suspected of heat stroke needs to be rapidly cooled without delay.
Treatment Options
- The most effective method of cooling is immersion in cold water up to the armpits. Hold the person to protect the head and mouth from submersion. If available, perform cold water immersion as soon as possible.
- If sufficient cold water is not available, douse the body and clothes, remove insulating clothing and socks.
- Get help or evacuate immediately.
Are you or a companion experiencing any symptoms consistent with heat stroke?
If yes, launch medical assessment below.
Low Salt Levels (Hyponatremia)
Hyponatremia (low salt levels) is a condition that arises from dilution of the salt levels in the body or overhydration. It can present as a wide variety of symptoms ranging from mild to fatal. Healthy young people have died from hyponatremia. Early recognition of the symptoms and appropriate treatment can be lifesaving.
Hyponatremia occurs by ingestion of large amounts of water or sports drink in excess of what the body gets rid of. Feeling of fullness, swelling of the hands and feet or bloating, and weight gain can be an early sign of your body retaining too much fluid, which puts it at risk for hyponatremia.
Symptoms of mild hyponatremia may appear similar to heat exhaustion: weakness, fatigue, irritability, headache, mild confusion, nausea and vomiting (often projectile), and may have very little or no urination despite normal amount of fluid intake, as the body is inappropriately retaining fluid.
Pay attention to fluid intake. If you are concerned about feeling unwell in the heat, and you have had more than 1 L / hour of recent water or sports drink ingestion, stop further fluid intake and rest to allow the body to urinate out the excessive fluid balance. Once urination occurs (which can take an hour or more), the symptoms usually start to resolve.
If available, consume salty snacks to help balance the salt levels in the blood. It is difficult to drink a solution that is salty enough to balance out the blood, so avoiding fluid intake is actually better than drinking more electrolyte-containing fluids, which can inadvertently worsen the hyponatremia.
Symptoms of severe hyponatremia may appear similar to heat stroke: collapse, altered level of consciousness, unsteady gait, seizures, unresponsiveness or in a coma. Altered mental status with vomiting, skin that doesn’t feel hot, shortness of breath or frothy sputum are also signs of severe hyponatremia.
Severe hyponatremia can be fatal. Awareness of mild symptoms and recent fluid intake history can help differentiate preceding mild hyponatremia from heat exhaustion, and severe hyponatremia from heat stroke.
Treatment Options
- If you have had more than 1 L / hour of recent water or sports drink ingestion, stop further fluid intake and rest to allow the body to urinate out the excessive fluid balance.
- If available, consume salty snacks to help balance the salt levels in the blood.
- Anyone with an altered level of responsiveness should initially be assessed and treated for possible heat stroke, and if the history is concerning for hyponatremia, it is safe to give salty foods, regardless of the cause – they need to be evacuated immediately.
Are you or a companion experiencing any symptoms consistent with hyponatremia?
If yes, launch medical assessment below.
Emergency Red Flags
Keep an eye out for the following symptoms. These red flags may be cause for evacuation.
- Altered level of responsiveness in the heat
- Persistent symptoms of heat exhaustion that do not improve
- Persistent symptoms of hyponatremia that do not improve with rest and fluid restriction
- Red/brown urine
- Passing out in the heat with concerning medical problems or with symptoms that do not improve with rest
- Too exhausted to continue the outdoor activity
If yes, launch medical assessment below.
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