Weather extremes can have adverse effects on human health, including concerns from severe heat and cold. Storms and harsh conditions, such as hurricanes and droughts, can create secondary dangers, including floods and wildfires. NIEHS has resources on many types of events and conditions.


man carrying boy in a flood

Weather extremes can have adverse effects on human health, including concerns from severe heat and cold. Storms and harsh conditions, such as hurricanes and droughts, can create secondary dangers, including floods and wildfires.

NIEHS has resources on many types of events and conditions, and some are included on this webpage.

Temperature Extremes


As a result of the changing climate, heat waves are happening more often. An increased number of extreme heat days or prolonged exposure to hot temperatures can harm your health. Extreme heat is a threat to human health worldwide, according to the World Health Organization.

A heat wave’s effects on human health can be difficult to track, but researchers are making progress. A NIEHS-funded study found that a period of unprecedented and dangerously high temperatures was associated with additional injury deaths in Washington state.

Heat-related illnesses include heat exhaustion, heat cramps, and heat stroke (also called sun stroke). Heat stroke, considered a medical emergency, occurs when a body's regulatory system fails to cool itself. As your body works to cool itself, blood rushes to the surface of your skin. As a result, less blood reaches your brain, muscles, and other organs, which can, in rare cases, cause brain damage or death.

Here are signs of stress from heat:

  • Dizziness
  • Fainting
  • Headache
  • Muscle cramps
  • Nausea or vomiting
  • Weakness

Read about extreme heat protection tips from the Centers for Disease Control and Prevention.

Urban Heat Islands

Rising temperatures and the associated health risks are not felt equally across populations. Cities tend to get much warmer than their surrounding landscapes. This localized increase in heat is known as the urban heat island effect and occurs as paved, dark surfaces found on roads and buildings trap more heat than vegetated landscapes. Highly developed urban areas can have mid-afternoon temperatures that are 15°F to 20°F warmer than surrounding green areas. Importantly, urban neighborhoods that were subjected to historical redlining typically lack green space and often suffer effects of heat islands.

High heat and air pollution each increase the chance of harms to human health. The combination of extreme heat and particulate air pollution is becoming more frequent because of climate change. NIEHS-funded researchers found that deaths rose on hot days and on days with high levels of fine-particulate air pollution. But on days when an area was hit with both high heat and high air pollution, the effects were much higher than for each condition alone.


Extremely cold air is seasonal in part of the U.S., affecting millions of people. It can lead to health problems and ice-related dangers, such as falls and car accidents. In cold weather, people without adequate shelter or who are stranded may have health emergencies.

Cold air acts as a vasoconstrictor, which means it narrows blood vessels, increasing risk of heart attack and strokes. Blood pressure tends to rise with exposure to cold.

Hypothermia is a condition in which the body's internal temperature falls too low. Acute hypothermia occurs with immersion in cold water or exposure to cold weather. Prolonged exposure to even mild cold can cause hypothermia. Signs that your body is not handling cold well include stiffness in the neck, arms, and legs.

Older adults, due to changes that come with aging, may lose body heat faster than younger people. The National Institute on Aging offers tips for Cold Weather Safety for Older Adults.

For people of all ages, the Centers for Disease Control and Prevention offers prevention tips for dealing with extreme cold.

What is NIEHS Doing?

NIEHS Efforts

  • Climate Change and Human Health – As the planet warms, oceans expand and the sea level rises, floods and droughts become more frequent and intense, and heat waves and hurricanes become more severe.
  • Disaster Research Response – NIH created a national framework for research on the medical and public health aspects of disasters and public health emergencies. The DR2 program provides tools, training, funding, and other support to empower human health research in response to disasters and public health emergencies.
  • Flooding and Hurricanes: Fugitive Chemical Health Risks – Coastal storms heighten the potential for hazardous chemicals to spread due to facility damage, storm surge, and flooding — creating "fugitive" chemicals.
  • Hurricanes & Floods - The NIEHS Worker Training Program and its awardees are involved in response to hurricanes and floods as well as cleanup activities after such disasters. Find free safety awareness and training resources for emergency responders, skilled support personnel, homeowners, and business owners.
  • Mold Exposure – The NIEHS Worker Training Program developed a Mold Cleanup and Treatment orientation for workers, volunteers, and homeowners who engage in small-scale mold cleanup and treatment of flooded or water-damaged homes.
  • Vectorborne and Zoonotic Diseases – Vectorborne and zoonotic diseases are infectious diseases whose transmission involves animal hosts or vectors.
  • Water-related Illnesses – Outbreaks of waterborne diseases often occur after a severe precipitation event (rainfall, snowfall).
  • Wildfires – From the NIEHS Worker Training Program, resources and training in support of wildfire response operations in the United States.

Further Reading

Stories from the Environmental Factor (NIEHS Newsletter)

Printable Fact Sheets

Fact Sheets

Climate Change and Human Health

Mold and Your Health

NIH Disaster Research Response (DR2) Program


  • Wildfire Smoke and Children's Health (2021) – This podcast explores the harmful effects of wildfire smoke on children's health and provides tips to keep kids safe during a wildfire event.

Additional Resources

  • ClimaHealth
    The World Health Organization (WHO) and World Meteorological Organization (WMO) are together advancing an integrated program of climate and health sciences and services to protect populations from the health risks of climate change.
    This website is the premier source of information regarding heat and health for the nation. It offers interactive maps, weather reports, tips for staying cool and other data to help you and officials across governments manage heat emergencies.
  • Heat-Related Illness EMS Activation Surveillance Dashboard (EMS HeatTracker)
    The HHS Office of Climate Change and Health Equity, in partnership with the National Highway Traffic Safety Administration, created an online information portal that maps emergency medical services responses to heat-related illness across the country.
    From the National Hurricane Center, an office of the National Oceanic and Atmospheric Administration.
  • NIH Climate Change and Health Initiative – This solutions-focused research initiative aims to reduce the health consequences associated with extreme weather events and evolving climate conditions. NIH has a strong history of creating innovative tools, technologies, and data-driven solutions to address global environmental problems.
    Ready is a national public service campaign designed to educate and empower the American people to prepare for, respond to and mitigate emergencies, including natural and man-made disasters.

Related Health Topics

For Educators

  • Climate Change and Human Health Lesson Plans – NIEHS developed learning modules suitable for use in high school and secondary school courses on earth, life, and environmental science, history, geography, health care or social studies classes. The modules challenge students to consider the complex interactions between environmental health and human health and prompts students to take action to improve their communities and design interventions to enhance climate resilience.