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Heat Illness
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Symptoms

Heat Illness

Heat illness occurs when the body's natural cooling mechanisms, such as sweating, are overwhelmed by high temperatures and humidity.

Overview

Your body normally cools itself by sweating. During hot weather, especially when it is very humid, sweating just isn't enough to cool you off. Your body temperature can rise to dangerous levels and you can develop a heat illness.

Causes & Risk Factors

Most heat illnesses happen when you stay out in the heat too long. Exercising and working outside in high heat can also lead to heat illness. Factors that increase your risk include:

  • Being an older adult or a young child
  • Being sick or overweight
  • Taking certain medicines
  • Drinking alcohol

Types of Heat Illness

  • Heat stroke: A life-threatening illness in which body temperature may rise above 106 °F (41 °C) in minutes. Symptoms include dry skin, a rapid, strong pulse, dizziness, nausea, and confusion. If you see any of these signs, get medical help right away.
  • Heat exhaustion: An illness that can happen after several days of exposure to high temperatures and not enough fluids. Symptoms include heavy sweating, rapid breathing, and a fast, weak pulse. If it is not treated, it can turn into heat stroke.
  • Heat cramps: Muscle pains or spasms that happen during heavy exercise. You usually get them in your abdomen, arms, or legs.
  • Heat rash: Skin irritation from excessive sweating. It is more common in young children.

Prevention

You can lower your risk of heat illness by drinking fluids to prevent dehydration, replacing lost salt and minerals, and limiting your time in the heat.

Frequently Asked Questions

Older adults, young children, and individuals who are overweight or sick are at higher risk because their bodies may not regulate temperature as effectively. People taking certain medications, such as diuretics or antihistamines, and those who consume alcohol are also more susceptible. High-risk individuals should limit time in the heat, monitor their fluid intake closely, and avoid alcohol, which can lead to dehydration. They should also check with their doctor about how their medications might affect their body’s ability to cool down and stay hydrated.
To prevent heat illness, stay hydrated by drinking water regularly before, during, and after activity, even if you do not feel thirsty. Replace lost salts and minerals with electrolyte drinks if you are sweating heavily. Wear light-colored, loose-fitting clothing to allow for ventilation. Take frequent breaks in shaded or air-conditioned areas, and avoid strenuous activity during the hottest parts of the day, typically between 10 a.m. and 4 p.m. Additionally, acclimatize to the heat gradually over several days if you are new to working in high temperatures.
Move the person to a cool, shaded, or air-conditioned area immediately. Have them lie down and elevate their legs slightly to help blood flow to the brain. Loosen or remove excess clothing and apply cool, wet cloths to the skin. Encourage them to sip water or an electrolyte drink slowly if they are fully conscious and able to swallow. Do not give them anything to drink if they are confused or unconscious. If symptoms do not improve within 30 minutes, or if they worsen, call emergency services immediately.
Heat exhaustion is characterized by heavy sweating, a fast but weak pulse, dizziness, nausea, and cool, pale skin. It is a precursor to heat stroke and can be treated by moving to a cool place and drinking fluids. Heat stroke is a life-threatening emergency where the body’s cooling mechanism fails, leading to a body temperature above 106 degrees Fahrenheit (41 degrees Celsius). Symptoms include dry or red hot skin, a rapid and strong pulse, confusion, and potential loss of consciousness. The distinction is critical because heat stroke requires immediate emergency medical intervention, such as rapid cooling, whereas heat exhaustion can often be managed with first aid if caught early.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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