Overview
Extreme heat means weather conditions that are much hotter than usual for a place, sometimes with high humidity. The body normally cools itself by sweating, but very hot conditions can overwhelm this process. This can lead to heat-related illness, especially during heat waves or when people cannot get enough shade, water, or cooling.
Key Symptoms
Early warning signs of heat illness can include heavy sweating, thirst, muscle cramps, tiredness, dizziness, headache, nausea, or fainting. As heat illness becomes more serious, symptoms may include confusion, trouble speaking, a fast pulse, very high body temperature, or hot skin. Heat stroke is a medical emergency.
Causes and Risk Factors
Extreme heat happens when environmental temperatures are high enough to raise body stress, especially when humidity is also high. Risk rises with hard physical activity, direct sun exposure, poor ventilation, dehydration, alcohol use, and lack of access to cooling. Some medications and chronic health conditions can also reduce the body's ability to handle heat.
Who Is Affected
Anyone can be harmed by extreme heat, but some groups face higher risk. These include older adults, infants and young children, pregnant people, outdoor workers, athletes, people with heart, lung, kidney, or mental health conditions, and people with disabilities. People who live alone, are unhoused, or lack air conditioning or reliable electricity may also be at greater risk.
Prevention
Stay in the coolest place available, use fans or air conditioning if possible, and spend time in public cooling spaces when needed. Drink fluids regularly, wear lightweight clothing, limit strenuous activity during the hottest hours, and check local heat alerts. Never leave children, older adults, or pets in parked vehicles, even for a short time.
Treatment Categories
For mild heat illness, common first steps include moving to a cooler place, resting, loosening clothing, and cooling the body with wet cloths or cool water. Fluids may help if the person is awake and able to drink. More serious symptoms need urgent medical care because severe heat illness can quickly damage the brain, heart, kidneys, and other organs.
Living With It
If you live in a hot climate or during a heat wave, plan daily routines around cooler hours and know where you can go for relief. Keep an eye on weather forecasts and heat warnings, and check on relatives, neighbors, and others who may need help. If heat affects your work, health, or housing, local public health or community services may offer support.
When to Seek Medical Care
Seek medical care promptly if heat symptoms do not improve after cooling down and resting, or if there is repeated vomiting, worsening weakness, fainting, signs of dehydration, or symptoms in a high-risk person. It is also important to ask a healthcare professional about heat risk if you take medicines or have a health condition that may affect sweating, fluid balance, or body temperature.
When It May Be an Emergency
Get emergency help right away for confusion, seizure, collapse, unconsciousness, trouble breathing, or signs of heat stroke such as very high body temperature and altered mental status. While waiting for help, move the person to a cooler place and begin cooling with cold water, wet cloths, or ice packs if available. Do not delay emergency care.