Also called: Heat exhaustion · Heat stroke · Sunstroke
Important: This page is general information, not medical advice. It does not recommend or prescribe any treatment. Always consult your doctor or pharmacist before starting, stopping or changing any medicine.
About Heat Illness
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.
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. Older adults, young children, and those who are sick or overweight are most at risk. Taking certain medicines or drinking alcohol can also raise your risk.
Heat-related illnesses include:
- 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.
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.
Centers for Disease Control and Prevention
It sits within Injuries and Wounds and Symptoms.
The lead U.S. institute for this subject is the National Institute on Aging.
When to speak to someone. Reading about a topic cannot tell you whether it applies to you. Speak to a doctor or pharmacist if symptoms are severe, sudden, getting worse, or simply not going away — and seek emergency care immediately for chest pain, breathing difficulty, sudden weakness or confusion, or a serious allergic reaction.
Research on Heat Illness
377 studies areregistered for this condition on ClinicalTrials.gov, the U.S. National Library of Medicine's public registry. A selection is below — the links go straight to the registry entry, not to a summary of ours.
What a registered study does and does not mean. Registration means a study exists and has been declared publicly. It says nothing about whether the treatment being tested works, is safe, or is available to you. Many studies find no benefit — that is what research is for. Never seek out an experimental treatment on the strength of a registry entry alone.
Research currently under way
- Impact of Extreme Heat on Myocardial Blood Flow and Flow Reserve in Young and Older AdultsUniversity of Texas Southwestern Medical Center
- Humidification Effects on Airway Complications and Clinical Outcomes in Trauma ICU Patients on Mechanical VentilationAssiut University
- Heat thErapy And mobiLity in COVID-19 SurvivorsUniversity of Nebraska
- A Study Comparing Whole-Body Heat Treatment Plus Systemic Therapy to Systemic Therapy Alone, for Advanced Pancreatic CancerElmediX
- Postoperative Re-irradiaTion With and Without HYPERthermia, or Surgery Only: Toxicity, Quality of Life and Survival in Patients With Locoregional Recurrent Breast CancerAmsterdam UMC, location VUmc
- Working in the Heat at Simulated Altitude: Effects of Normobaric Hypoxia on Physiological StrainUniversity of Ottawa
Research already completed
- Randomised Clinical Trial in Treatment Modalities for Cutaneous Leishmaniasis Caused by Leishmania Tropica, in PakistanMedecins Sans Frontieres, Netherlands
- The Effect of Isometric Exercise and Dry Heat Application on PIVCInonu University
- Identifying the Limits of Survivability in Heat-exposed Older FemalesUniversity of Ottawa
Study data from ClinicalTrials.gov, a service of the U.S. National Library of Medicine. Retrieved 2026-07-30. Registry entries are supplied by study sponsors and investigators; ClinicalTrials.gov does not verify their scientific validity. PocketsInfo is not affiliated with, and not endorsed by, the NLM or the NIH.
Where to read more
Rather than paraphrase, we point you to the primary sources. Every link below is to a government health agency, a national institute or a recognised medical body — grouped by what you are trying to find out.
Start Here
- Extreme HeatDepartment of Homeland Security
- Extreme Heat and Your HealthCenters for Disease Control and Prevention
- Hot Weather Safety for Older AdultsNational Institute on Aging
Symptoms
- About Heat and Your HealthCenters for Disease Control and Prevention
Treatments and Therapies
- First Aid for Heat ExhaustionVisualDX
- Heat Cramps, First AidVisualDX
- Heatstroke, First AidVisualDX
Prevention and Risk Factors
- Beat the Heat: Staying Safe in the SummertimeNational Institutes of Health
- Extreme Heat SafetyAmerican Red Cross
Related Issues
- Protect Your Heart in the HeatAmerican Heart Association
- Safety Tips for Hot Weather ExerciseMayo Foundation for Medical Education and Research
Clinical Trials
- ClinicalTrials.gov: DehydrationNational Institutes of Health
- ClinicalTrials.gov: Heat Stress DisordersNational Institutes of Health
Medical subject headings
Clinicians and researchers index this subject under Heat Stress Disorders. These are the terms to use when searching medical literature.
This page is built from the MedlinePlus health topic record for Heat Illness, a service of the U.S. National Library of Medicine (NLM), National Institutes of Health. Information is from MedlinePlus.gov. PocketsInfo is not affiliated with, and is not endorsed by, the NLM or the NIH. Retrieved 30 July 2026.