Weather Extremes

Weather extremes, including severe heat and cold, wildfires, storms, hurricanes, droughts, and floods can have adverse effects on human health.

Overview

Extreme weather events have a growing impact on human health around the world. These events include droughts, heat waves, wildfires, floods, tornadoes, and hurricanes.

Extreme weather, including very hot or very cold temperatures, can harm people in direct ways like heat stroke or hypothermia. Weather also can affect people indirectly. Flooding from heavy rains and hurricanes can increase exposure to harmful chemicals and infectious pathogens and can allow mold to grow. Severe heat and drought can lead to wildfires that send smoke and particles into the air. While everyone faces risk, older adults, outdoor workers, pregnant women, infants, children, and people with chronic health conditions are especially susceptible. Exposure in utero and during early life, including infancy and childhood, may have lasting effects on health and development.

Being prepared before a weather disaster can make a life-saving difference.

Related Health Effects

Pregnancy and Fetal Development

Pregnancy is a sensitive period during which environmental exposures can affect both maternal and fetal health. Emerging research suggests that environmental stressors during pregnancy may influence fetal development, highlighting the importance of protective measures. The placenta regulates oxygen, nutrients, and waste exchange between mother and fetus, and changes in the maternal environment can influence these processes.

Extreme heat can lead to dehydration and place stress on the body’s ability to regulate temperature.

Air pollution, including particles from wildfire smoke, is associated with respiratory and cardiovascular effects.

Flooding and disasters can:

  • Disrupt access to prenatal care
  • Increase exposure to infections and environmental hazards
  • Contribute to stress and mental health challenges

Heat-Related Health Effects

Heat-related illnesses include acute events like heat exhaustion, heat cramps, and heat stroke. Heat stroke occurs when the body’s regulatory system fails. As the body works to cool itself, blood rushes to the surface of the skin, which means less blood reaches the brain, muscles, and other organs. This can cause nausea, dizziness, confusion, and even seizures. In rare cases, heat stroke can lead to brain damage or death.

Heat waves and thunderstorms similarly have been tied to outbreaks of allergic asthma, especially in people with pollen allergies. Exposure to heat can also make many chronic disease conditions worse, with examples including cardiovascular disease, diabetes, and mental health conditions. Heat can have negative interactions with certain medicines, affecting efficacy and the body’s thermoregulation abilities.

High heat and drought conditions increase the risk of wildfires. Particles in the smoke from these wildfires may cause lung and heart problems, respiratory infections, and asthma. Recent studies also suggest that wildfire smoke particles may increase the risk of dementia in older adults.

Warmer nighttime temperatures lower sleep quality. Poor sleep and tiredness can lead to memory issues, depression, high blood pressure and other health problems.

Cold-Related Health Effects

Extreme cold also negatively affects health. Cold air acts as a vasoconstrictor, which means it narrows blood vessels. This often leads to a rise in blood pressure during cold exposure and increases the risk of heart attack and stroke.

Hypothermia occurs when the body’s core temperature falls below 95°F. This drop can lead to serious health effects like irregular heartbeat, heart failure, and damage to the kidneys or liver. Hypothermia is common in very cold weather. It can also occur at cool temperatures above 40°F if a person becomes chilled from rain, sweat, or cold water.

Many of injuries related to cold exposure occur in the home. One of the most common is an increased risk of heart attack in older adults while shoveling snow.

Flood-Related Health Effects

Floods occur across the United States and bring with them a variety of health concerns. Flooding events have been linked to injuries from debris, infections, diseases from parasites, heart and lung conditions and higher death rates.

When flood waters pour into homes and schools, they can cause mold to grow. Contact with mold over long periods can lead to lung allergies, asthma in children, and problems with thinking and memory.

Flooding and other disasters can have significant mental health effects. Loss of property, displacement, and disruption of daily life may lead to short-term distress as well as longer-term conditions such as anxiety, depression, and post-traumatic stress disorder (PTSD).

Risk Factors

Events like hurricanes, tornados, and wildfires can cause immediate injury. Flood waters that carry bacteria, sewage, and hazardous chemicals can cause sickness over a longer period. People living in areas that experience wildfires, flooding, or frequent storms should be alert to risks.

Certain groups also face special risks from extreme weather conditions. Vulnerability to extreme weather is influenced by a combination of biological and social factors. These include differences in how the body responds to temperature, underlying health conditions, access to resources such as housing and health care, and reliance for care.

Older Adults

Older adults typically do not adjust as well as others to sudden temperature changes. They are more likely to have medical conditions that limit the body’s ability to adjust to extreme heat. Factors that put older adults at greater risk for heat-related illness include:

  • Skin changes caused by normal aging
  • Illnesses that cause weakness or fever
  • Taking diuretics, sedatives, tranquilizers, and some heart and blood pressure medicines
  • Use of several prescription drugs at the same time
  • Being overweight or underweight
  • Not enough fluid intake and dehydration

Older adults also face greater health risks from extreme cold. Many lose body heat faster than younger people. Some have medical conditions like diabetes, thyroid problems, and Parkinson’s disease that make it even harder to stay warm in cold weather.

Extreme weather can also cause mental health issues in older adults. People forced from their homes by weather disasters may experience social isolation, loneliness, and depression.

Infants and Children

Infants are at a high risk of dangerous overheating, called hyperthermia. Their bodies can’t cool down easily, and they aren’t able to tell us when they are too hot.

Hyperthermia happens when the body reaches 104°F. A body temperature of 107°F is usually deadly. Hot cars are a special concern. Even on a comfortable 72°F day, the inside of a car can reach over 100°F in just 30 minutes. Leaving windows slightly open does not stop the car from getting dangerously hot.

Children are also vulnerable to environmental exposures such as air pollution, wildfire smoke, mold, and contaminants associated with flooding, which can worsen respiratory conditions like asthma. Disruptions caused by extreme weather and disasters, including displacement, school closures, and changes in daily routines can increase stress and anxiety in children and affect their learning and social development. Protecting health during early life is especially important because environmental exposures during these critical periods can influence health across the lifespan.

Urban Residents

People living in cities also can face greater health risks from rising temperatures. Cities are often much hotter than rural and suburban areas because roads and buildings trap heat. Within cities, neighborhoods without parks and green spaces can be 15°F to 20°F hotter than nearby areas with more trees and plants. People who live in these “urban heat islands” often experience more health effects during times of extreme heat.

Prevention Guidance

Disaster preparation:

  • Learn what kinds of disasters are most likely to affect you based on where you live.
  • Know about evacuation routes and locations of shelters.
  • Store important documents in a fireproof and waterproof container and save digital copies.
  • Create an emergency kit with three to seven days of supplies.

Emergency kits items:

  • Water (one gallon per person per day)
  • Food (at least a several-day supply of nonperishable food) and a manual can opener
  • Battery-powered or hand-cranked radio
  • Flashlight or headlamp with extra batteries
  • First-aid kit
  • Dust masks, plastic sheeting, and duct tape to help filter contaminated air
  • Soap, hand sanitizer, and personal hygiene supplies
  • Cell phone with chargers and a backup battery
  • Sleeping bags or warm blankets
  • Over the counter and prescription medicines
  • Essential health information and important family documents

Extreme heat safety:

  • Drink plenty of liquids such as water, fruit or vegetable juices, or drinks with electrolytes.
  • Avoid alcohol and caffeinated beverages.
  • If your home lacks air conditioning, spend time during midday in a place that has it such as a shopping mall, library, or senior center.
  • Wear lightweight, light-colored, loose-fitting clothing made of natural fabrics such as cotton.
  • Avoid outdoor exercise and physical activity when it is very hot.
  • Use sunscreen with SPF 15 or higher and reapply throughout the day.
  • Wear a hat, protective clothing, and sunglasses.
  • Ask your doctor if your medicines make you more likely to become overheated or sunburned.
  • Get out of the sun and into a cool place. Find an air-conditioned space if possible.
  • Shower, bathe, or sponge off with cool water.
  • Lie down and rest.
  • Ensure children stay hydrated and avoid prolonged exposure to extreme heat.
  • Monitor children for signs of heat-related illness.
  • Plan ahead for essential supplies, including medicine and infant care needs.
  • Identify safe indoor spaces during extreme temperatures.
  • Never leave a child alone in a car, not even with the windows down, and not even for a minute.
  • Develop plans to ensure that no one is left in a car by accident.

Extreme cold safety:

  • Check the weather forecast and try to stay inside on cold, windy days.
  • Wear a hat, scarf, and gloves or mittens to prevent loss of body heat.
  • Use loose layers of clothing — the air between layers helps keep you warm.
  • Wear a waterproof coat or jacket if it is snowy or rainy.
  • Change out of damp or wet clothes as soon as possible.
  • Set your home heat to at least 68°F. Even temperatures from 60°F to 65°F can lead to hypothermia in older adults.
  • Avoid alcohol or limit intake. Alcohol can cause the body to lose heat.
  • Ask someone to check on you during cold weather.
  • Avoid shoveling snow if you are older or have existing heart conditions.
  • To help reduce the risk of falls in icy and snowy weather:
  • Keep outside walkways clear of snow and ice with an ice melt product or sand.
  • Use railings to help avoid slipping on icy stairs and walkways.
  • Wear nonskid, rubber-soled, low-heeled footwear.

Find a Clinical Trial

Clinical trials uncover better ways to prevent, diagnose, treat, and understand diseases and conditions. To ensure results apply to everyone, volunteers of all ages, sexes, and backgrounds, including both healthy individuals and those with specific medical conditions, are needed. Find clinical trials by searching for health topics at Weather Extremes.

Find Treatment

For heat-related Illness:

  • Heat syncope (sudden dizziness): Rest in a cool place, put your legs up, and drink water.
  • Heat cramps: Stop physical activity, rest in shade or a cool building, and drink plenty of fluids with electrolytes.
  • Heat edema (swelling in ankles and feet): Put your legs up. If swelling does not go away quickly, check with your doctor.
  • Heat rash: Keep the area dry and use powder to soothe the rash. Stay in cool areas.
  • Heat exhaustion: Rest in a cool place and drink plenty of fluids. Get medical care if you do not feel better soon.
  • Heat stroke: Seek medical help right away. Move to a cooler place. Bring down your body temperature with cool clothes, a cool bath or shower, and fans.
  • Sunburn: Wear lightweight clothing, take cool showers, and moisturize affected areas. Stay out of the sun.

For cold-related illness:

  • Hypothermia is a medical emergency. If someone shows signs of hypothermia, call 911 right away. Try to move the person to a warmer place, offer them a warm drink, and wrap them in dry blankets, towels, or coats.
  • Protect any exposed skin and get out of the cold as quickly as possible to prevent frostbite from getting worse.

Community Support

Note: This resource list is for informational purposes only. It is not comprehensive, and an organization’s inclusion does not constitute an endorsement by NIH. 

Research Information

The National Institutes of Health (NIH) is the largest public funder of biomedical research in the world. NIH invests most of its budget in medical research seeking to enhance life and to reduce illness and disability. NIH-funded research has led to breakthroughs and new treatments helping people live longer, healthier lives, and building the research foundation that drives discovery.

NIH Disaster Research Response Program (DR2)

NIH has created a national program to promote timely health research in response to disasters and emergencies to reduce adverse health impacts and further preparedness and recovery efforts. The program offers training, ready to use and easy to find tools, and support for health researchers after extreme weather events or other disasters.

NIH Program on Health and Extreme Weather

The NIH Program on Health and Extreme Weather (HEW) supports research across the nation to study how extreme weather affects human health and to find solutions to reduce harmful impacts. NIH-supported research also examines how extreme weather affects populations across the life course, including pregnant women, infants and children.

Exploratory Research Centers

Scientists at HEW-funded centers across the U.S. study how extreme weather affects our health. These centers work to find practical, real-world solutions that keep people safe during extreme weather. Their goal is to help everyone—from single individuals to entire communities—become stronger and better prepared to handle extreme weather events and conditions.

Alliance for Community Engagement – Partnership for Action Toward Health

The Alliance for Community Engagement – Partnership for Action Toward Health, part of NIH’s Community Engagement Alliance (CEAL), partners with research teams at the University of Alaska Fairbanks, the University of Colorado Denver, and the Public Health Institute to support research conducted through academic–community partnerships. These community engagement hubs support collaborative efforts to better understand the health impacts of extreme weather and to co‑develop and test interventions with communities to address prioritized local health stressors. These efforts seek to support the adoption of community‑driven solutions informed by community priorities and local context.

NIH-NSF Funded Support for Rapid Response Disaster Research

Through the HEW Program, NIH has partnered with the National Science Foundation (NSF) to support two major research centers that help us understand health risks associated with extreme weather. The University of Colorado Boulder Natural Hazards Center provides funding so that scientists can conduct timely research quickly after extreme weather events before health data is lost. The University of Washington RAPID Facility provides researchers with instrumentation, software, and support needed to collect and process perishable data from disasters.

Find NIH-funded research projects using NIH RePORTER, a searchable database of current and past research projects supported by NIH and other federal agencies.