We have compiled key information to help you make decisions. Scroll through the page or navigate to the topic of interest to you:

What is extreme heat?

Extreme heat events, or excessive heat events, are long stretches of heat with little relief that are significantly hotter or more humid than expected for the time of year. Extreme heat events and heat-related deaths have been increasing each year in the United States. Climate projections show that extreme heat events will become more common and intense.

While temperature is an important part of extreme heat events, humidity, length of time, and how unusual the heat is for the time of year and location all contribute to the danger of extreme heat. High humidity can increase heat strain. How long the heat lasts and how unusual it is impacts how well prepared people are and what actions they choose to take.

Extreme heat levels and what they mean

The National Weather Service (NWS) provides a heat index to help us to understand how heat and humidity impact us. The heat index shows what the temperature feels like to our bodies based on the temperature and relative humidity. As the air temperature and relative humidity increase, the heat index increases. 

To better understand how exposure to heat and humidity affects the body, NWS provides this chart.

CDC and NOAA have also developed a tool to help you determine your local heat risk level. The tool provides general guidance on heat risk and recommended actions to take to protect yourself.

How extreme heat events affect health

Heat can affect people in many different ways. Age, medications, pre-existing conditions, and many other factors can make people vulnerable when the temperature rises. It’s not always heat alone that can impact your health. Heat combined with high humidity, low wind, and prolonged exposure can leave people vulnerable.

When we experience prolonged periods of heat, our bodies have to work hard to cool down. This work can stress our hearts and kidneys. In serious cases, heat exposure can cause heat-related illnesses. Heat-related illnesses include heat rash, sunburn, heat cramps, heat exhaustion, and heat stroke.

Heat cramps, heat exhaustion, and heat stroke are the most serious heat-related illnesses. Recognizing the signs and symptoms of heat illness can protect you or your loved ones during a heat emergency. For detailed information about symptoms of heat-related illnesses, please refer to our Impacts of Extreme Heat page.

Extreme heat can be much more dangerous if you have pre-existing health conditions, such as cardiovascular disease, respiratory conditions, diabetes, and mental health conditions.

When planning for or responding to an extreme heat event, priority groups include people who are more likely to be exposed to extreme heat, people who are more likely to be sensitive to extreme heat health effects, and people facing high socioeconomic burdens.

For more detail about protecting protect priority at-risk populations during extreme heat events, please refer to our Priority Populations webpage.

How to Interpret HeatRisk

HeatRisk forecasts health impacts of heat. The product combines health and temperature data to produce a 7-day outlook for possible health effects from heat. The product is sensitive to abnormal heat durations, humidity, location, and different seasons of the year. 

The product uses an easily interpretable 5-category scale to show how risky the heat is for our health.

Green, or category 0, indicates that there is little or no risk from expected heat. 

Yellow, or category 1, indicates that there is minor risk from the expected heat. People who are sensitive to heat may be at risk. When the risk is category 1, be sure to remain hydrated and try to cool off. If you are on medications that disrupt temperature regulation, speak with your healthcare provider. 

Orange, or category 2, indicates that there is moderate risk from expected heat. Heat-sensitive people and individuals with prolonged heat exposure may be at risk. In addition to following advice listed for category 1, it is advised that people spending time outside take breaks, do activity at cooler parts of the day, and stay in shade. It is also advised that people use air conditioning indoors or go to a cooling location and use a fan to cool off (only when indoor temperatures are under 90 degrees Fahrenheit). 

Red, or category 3, indicates that there is major risk from expected heat. Most people are at risk of health effects, especially workers, athletes, unhoused people, and people with prolonged heat exposure. When the heat risk is category  3, there are also risks of power outages. In addition to following advice listed for both categories 1 and 2, it is strongly advised to move outdoor activities to a cooler day. If you have to be outside, remain in the shade as much as possible. 

Magenta, or category 4, indicates that there is extreme risk from expected heat. Everyone is at risk of health effects. Power outages and increased strain on health systems can occur. In addition to following the advice listed for categories 1, 2, and 3, it is strongly advised that you remain in air conditioning as fans may not be able to cool you off in these temperatures. If you do not have air conditioning, a cooling center nearest to you can be located on the New York State Cooling Center Finder Map or New York State Cooling Center Finder List. 

How to interpret Heat and Health Tracker
The Heat and Health Tracker shows the rate of emergency department (ED) visits associated with heat-related illness per 100,000 ED visits. The Heat and Health Tracker combines temperature data and surveillance data for heat-related illnesses and emergency department visits. 

Heat and Health Tracker allows users to observe daily heat-related illness rates over a 24 hour period. The product shows health burden related to heat by county and/or by regions defined by the Department of Health and Human Services.

How to interpret Heat and Health Index

The Heat and Health Index (HHI) combines historical temperature data, heat-related illness data, and community characteristics data at the ZIP code level to identify communities where people are most likely to feel effects of heat on their health. Community characteristics integrated into the HHI include sociodemographic indicators, natural and built environment indicators, and burden of pre-existing health conditions associated with heat. 

This product can help you understand the risk to your community during a heat event.

Equity Considerations

As a decision maker, there are likely some situations that seem like there’s no perfect answer: how do I protect the majority of the population, while also recognizing that there will be challenges for some. This is the public health paradox. 

We have presented four case studies to help you to consider pros and cons:

• Workers
• Older Adults
• People with Low Incomes
• People Experiencing Homelessness or Living in Substandard Housing

In addition to reaching all people in a community, it is important to provide translated materials and non-written (e.g., verbal or video) communications. This can expand the reach of information and reduce confusion and misunderstandings, improving knowledge of heat-related health effects and of the steps to take to minimize exposure risk. 

For a list of resources in different languages, refer to the Resources in Non-English Language page. For a list of non-written communications, refer to the Videos and Infographics page. 

Educational materials, information on extreme heat, and recommendations to protect health should come from trusted sources in the community, including local organizations such as community centers, schools, churches, and public officials. Working with trusted sources can improve the acceptance of information within the community, benefiting overall community health during extreme heat events.

If you are considering how to mitigate risks for the community, please refer to the Community Risks page. The page includes information on risk mitigation in schools and daycares, workplaces, and hospitals.

How to protect you and your staff outside

Regularly monitor the heat in an area. OSHA recommends that all workplaces use the wet bulb globe temperature (WBGT) to understand heat risk. WBGT includes air temperature, humidity, radiant heat from sunlight or other heat sources, and air movement. For interpretation of WBGT, please refer to the table below from the National Weather Service.

If you cannot measure WBGT, you can also use the heat index, which accounts for temperature and humidity. 

To better understand how exposure to heat and humidity affects the body, NWS advises that: 

• When the Heat Index is 80 – 90 ℉, fatigue is possible with prolonged heat exposure and/or physical activity. 
• When the Heat Index is 90 – 103 ℉, heat-related illnesses are possible with prolonged heat exposure and/or physical activity.
• When the Heat Index is 103 – 124 ℉, heat cramps or heat exhaustion are likely and  heat stroke is possible with prolonged heat exposure and/or physical activity.
• When the Heat Index is 125 ℉ or higher, heat stroke is likely.

During extreme heat events, the best strategy to protect your and others’ health is to limit time spent outdoors in the heat. If you must work outdoors, be sure to take breaks and ensure proper hydration of all staff members. 

Another important part of heat safety at the workplace is acclimatization. Heat acclimatization is an improvement in heat tolerance from gradually increasing the intensity or duration of work in heat. Workers who are new to high heat environments are at a higher risk of heat-related illness. Refer to NIOSH’s guidance on heat acclimatization and/or to our Community Risks page for more detail on heat acclimatization.

How to protect you and your staff indoors

During extreme heat events, turning on air conditioning and increasing airflow can make the workplace safer for workers. Furthermore, changing work schedules to reduce extreme heat exposure, to increase the number of breaks, and to minimize strenuous activity indoors also protects employees. Supervisors should advise staff to stay hydrated and should educate themselves and their staff about the symptoms of heat-related illness.