Heat exhaustion occurs when your body gets too hot. The hypothalamus is the part of the brain that controls thirst and hunger. It also controls the body's core temperature. Normally, the body cools itself by sweating. When you are exposed to high temperatures for a long time (for example, when working outdoors in the summer) and don't replace the fluids you lose, the body systems that regulate temperature become overwhelmed. As a result, your body produces more heat than it can release. Heat exhaustion requires immediate attention because it can progress to heat stroke, a life-threatening illness.

People with heat exhaustion may experience the following signs and symptoms:

• Sweating
• Fatigue
• Headache
• Pale, clammy skin
• Thirst
• Rapid heartbeat
• Dizziness, fainting
• Nausea, vomiting
• Muscle and abdominal cramps
• Mild temperature elevations
• Weakness

Heat exhaustion may occur when the core body temperature raises to below 104°F (40°C). If the core body temperature goes above 104°F (40°C), or if coma or seizure occurs, the patient may have heat stroke.

• Core temperature above104°F (40°C)
• Dehydration
• Neurological manifestations such as seizures, tremors, hemiplegia, and coma

If left untreated, heat stroke can quickly lead to heart attack and death.

Heat exhaustion occurs most often when you are exposed to high temperatures and become dehydrated, usually from not drinking enough fluids. It can also happen when you replace large volumes of sweat with fluids that do not contain enough salt.

Heat stroke is classified as:

• Exertional heat stroke occurs despite normal functioning of the body's heat regulation mechanisms. For example, exertional heat stroke may be experienced by young healthy people after strenuous physical work in warm and humid conditions.
• Non-exertional heat stroke occurs due to a failure of the body's temperature regulation system. Non-exertional heat stroke is more likely to occur in older individuals who may have chronic health conditions.

The following factors increase the risk of developing heat exhaustion:

• Being dehydrated
• Age (the elderly above age 65 years and children under age 15 years)
• Illness or chronic disability
• Obesity
• Pregnancy
• Cardiovascular disease
• Hypertension
• Respiratory disease
• Drinking alcohol
• Physical exertion in hot or humid environments (athletes, military personnel, and outdoor laborers are at high risk)
• Taking medications that interfere with the body's ability to cool itself, including antipsychotics, tranquilizers, antihistamines, tricyclic antidepressants, beta-blockers, and some over-the-counter sleeping pills

If you have symptoms of heat exhaustion, you should see a doctor immediately. The doctor will perform a physical examination, check your blood pressure, pulse, and temperature, and assess how dehydrated you are. The doctor may also request lab tests of blood and urine samples.

Prevention

If you are working or exercising in the heat, drink plenty of fluids before, during, and after the activity. Take the following precautions to prevent heat exhaustion:

• Try to stay in cool or air conditioned spaces on hot days.
• Drink cool water or sports drinks. Drink more fluids than usual. Drinking fluids during exercise improves heart function, maintains kidney function, and lowers the body's core temperature. Dehydration can stress the heart and reduce the kidneys' ability to maintain the correct balance of electrolytes (charged elements -- such as potassium, sodium, phosphorous, and chloride -- which are essential for the normal function of every cell in the body).
• Check in regularly with people who are vulnerable to heat exhaustion (for example, the elderly and children).
• Avoid alcohol.
• Plan for exercise or work outdoors during cooler times of day.
• Take cool baths.
• Wear loose, lightweight clothing.
• Long-term prevention of heat exhaustion includes regular, doctor-approved exercise. Those who exercise regularly over time, allowing their bodies to adjust to hot conditions, may better tolerate activity on warm days.

Treatment Plan

The primary treatment for heat exhaustion is to rest in a shady spot or, better, an air-conditioned room, and to drink cool (not icy) fluids. You can lower core body temperature by immersing yourself in cold water or spraying yourself with cold water and fanning. Water is usually enough to reverse dehydration, but you can also drink a sports drink that contains electrolytes.

Drug Therapies

Your health care provider may recommend an oral or intravenous saline electrolyte solution.

Complementary and Alternative Therapies

Nutrition and Supplements

Providers may recommend drinking fluids that contain electrolytes (see Prevention section). Endurance athletes may want to take mineral supplements, including:

• Calcium
• Magnesium
• Potassium

Foods high in these nutrients include dark leafy greens, nuts, seeds, whole grains, sea vegetables, blackstrap molasses, and bananas. Please note: Taking any of these minerals in large amounts may cause unwanted symptoms and/or mineral imbalances. Consult your doctor to determine the correct amount of mineral supplementation to meet your needs.

Herbs

The most important treatment for heat exhaustion is replacing lost fluids by drinking cool water or a sports drink, and getting into a cooler environment. If you have symptoms of heat exhaustion you should talk to your provider before taking anything. Although no studies have examined using herbs to treat heat exhaustion specifically, the following herbs are sometimes used by people with fever:

• Yarrow (Achillea millefolium) is sometimes used to treat fever. Do not take Yarrow if you are pregnant or nursing. Yarrow should not be taken with blood-thinning medications, such as warfarin (Coumadin), and should be discontinued at least 2 weeks before any surgery. Yarrow can also interact with lithium and other sedative medications. Yarrow can increase perspiration - this may lead to further dehydration and exacerbate heat stroke. Do not use Yarrow to treat heat stroke or overheating caused by exposure to excessive heat or exertional heat stroke. People with allergies to Rag Weed may react to Yarrow.

Homeopathy

Although few studies have examined the effectiveness of specific homeopathic therapies, homeopaths may consider the following remedies for the treatment of fever:

• Belladonna
• Glonoinum

If you avoid heat stroke, recovering from heat exhaustion usually takes 24 to 48 hours. Depending on the severity of heat exhaustion, you may be hospitalized so doctors can monitor your fluid and electrolyte levels to avoid complications. Delayed access to cooling is the leading cause of complications among people with heat stroke. Heat exhaustion can exacerbate a wide range of medical conditions.

Your health care provider will check the fluid levels in your body to see if electrolyte replacement should be continued.

Bergquist PE. Therapeutic homeopathy. In: Rakel D, ed. Integrative Medicine. 4rd ed. Philadelphia, PA: Elsevier Saunders; 2018:chap 115.

Cheshire WP Jr. Thermoregulatory disorders and illness related to heat and cold stress. Auton Neurosci. 2016;196:91-104. PMID: 26794588 www.ncbi.nlm.nih.gov/pubmed/26794588.

Ferri FF. Heat exhaustion and heat stroke. In: Ferri FF, ed. Ferri's Clinical Advisor 2018. Philadelphia, PA: Elsevier; 2018:561-562.e1

Grove AJ, Gomez J. Environmental illness. In: Miller MD, Thompson SR, eds. DeLee and Drez's Orthopaedic Sports Medicine. 4th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 25.

Kravechenko J, Abernathy AP, Fawzy M, Lyerly HK. Minimization of heatwave morbidity and mortality. Am J Prev Med. 2013;44(3):274-282. PMID: 23415125 www.ncbi.nlm.nih.gov/pubmed/23415125.

Masur LC. Mineral status evaluation. In: Pizzorno JE, Murray MT, eds. Textbook of Natural Medicine. 4th ed. Philadelphia, PA: Elsevier Churchill Livingstone; 2013:chap 24.

Platt M, Vicario S. Heat illness. In: Marx JA, ed. Rosen's Emergency Medicine. 8th ed. Philadelphia, PA: Elsevier Saunders; 2014:chap 141.

Sakwa MN, O'Connor FG. Disorders due to heat and cold. In: Lee G, Schafer AI, ed. Goldman-Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier; 2016:chap 109.

Yamazaki F. Effectiveness of exercise heat acclimation for preventing heat illness in the workplace. J UOEH. 2013;35(3):183-192. PMID: 24077586 www.ncbi.nlm.nih.gov/pubmed/24077586.