Each year, there are about 700 heat-related deaths in the United States. In 2022, 707 Massachusetts residents visited the emergency department (ED) and 87 were hospitalized for heat-related illness (HRI). In the last decade, HRI has caused 30 deaths in Massachusetts.
Age and health status are important risk factors for HRI. However, social, economic, and environmental factors also play important roles. These factors can be especially impactful during periods of extreme heat. This is because resources for staying cool are not always equitably distributed.
The Intergovernmental Panel on Climate Change (IPCC) is a group of scientists working on climate-related projects for the United Nations. The IPCC predicts that climate change will cause increasing heat waves. We can also expect to see longer warm seasons. In turn, the prevalence of HRI is also expected to grow.
You can use the display to review HRI hospitalization or ED rates for any city or town in Massachusetts.
What is heat-related illness?
Heat-related illness (HRI) is also known as heat stress. HRI refers to a group of health conditions resulting from exposure to high temperatures. In these conditions, the body becomes unable to properly cool itself and body temperature rapidly rises. HRI can also occur or worsen with physical activity or when accompanied by other diseases.
For more information about the signs and symptoms of HRI, visit the Prevent and treat heat-related illness webpage.
What causes HRI?
HRI is caused by exposure to high temperatures, particularly during high humidity and physical activity. Body temperature is regulated through sweating and other processes. However, when exposed to high temperatures, the body may not be able to cool itself. This will raise the body's core temperature, and can lead to HRI.
Who is at risk for HRI?
Any individual can develop HRI if engaged in physical activity or exposed to heat and humidity. The following factors can increase a person’s risk for developing HRI:
Health
People with chronic health conditions may be more affected by the heat. Common conditions that increase risk include:
Heart disease
Stroke
Kidney disease
Diabetes
Obesity
Age
Older adults (age 65 and older) can be at greater risk of developing HRI. This is especially true for those who live alone or have chronic health conditions. These health conditions may make it difficult to regulate body temperature. Prescription medications may also play a role. More information and resources for adults aged 65+ can be found at the Executive Office of Aging and Independence – Preparing for extreme heat.
The very young can also be more vulnerable to health impacts. Infants have a harder time regulating their body temperature due to their small size. They are also unable to dress themselves and can't make decisions that can help regulate their temperature.
Work-related exposure
Both indoor and outdoor workers may be more likely to be exposed to hot environments. Some jobs also require increased physical activity. This can increase the risk of developing HRI. For more information on occupational risk for HRI, check out the MA Labor and Workforce - Best practices for preventing health illness. It is available in both English
Social determinants of health
Our health is impacted by the social determinants of health (SDoH). These are the social, economic, and physical factors where we work, live and play.
Income, living conditions, and the neighborhood you live in can impact a person’s exposure to heat. For example, those experiencing homelessness spend more time outdoors. They may lack resources for reducing heat exposure, especially during the summer. They may also have limited resources to find alternative shelter during a heat wave. Those living with low incomes may not be able to afford air conditioning and live in small spaces. Those who rent may be reliant on a landlord to make changes that would reduce heat exposure.
How can you prevent heat stress and HRI?
Heat-related illnesses and deaths are preventable. Here are some tips for avoiding HRI:
- Stay inside in the air conditioning or contact your local health department to locate an air-conditioned shelter in your area
- Drink plenty of water
- Wear loose, lightweight clothing
- Use a buddy system - check on a friend or neighbor during extreme heat events
- Plan outdoor activities during the early morning, late afternoon, and evening hours
- Know the signs of heat stress and act quickly if you feel the symptoms or someone you know shows signs
- Employers should provide training so workers understand what heat stress is and how it can be prevented
Looking to add a cooling system? Programs like Mass Save may be able to help.
Why does MA EPHT track HRI?
The relationship between extreme heat and increased illness and death is well established. Rates for heat-related illness are indicators of the impact of a changing climate.
MA EPHT tracks ED visits and hospital admissions for HRI in each community in Massachusetts. Tracking these data can help document changes in heat exposure over time and place. We can also identify and monitor vulnerable populations. This information allows us to evaluate the results of local climate adaptation strategies.
Available data
Use the Explore HRI hospitalization data link on this page to access the following measures for heat-related illness:
- Annual number of hospitalizations / ED visits
- Annual crude rate per 100,000 population
- Annual age-adjusted rate per 100,000 population
- Explore data in tables, charts, and maps
MA EPHT presents case counts and crude rates on HRI emergency department and hospital admissions for the following geographies: city/town, county, EP region, EOHHS region, and statewide. Measures are offered by a combination of year, age group, and sex. The most current data available is shown. Be sure to check the site periodically as new data is added. To protect privacy, no information is shown that could potentially identify an individual.
Related links
Additional resources
Massachusetts
- Massachusetts Emergency Management Agency (MEMA) extreme heat safety tips: Guidance on staying safe during hot weather
National
- National Oceanic and Atmospheric Administration (NOAA) heat wave brochure: Describes heat-related illness symptoms, first aid, and safety tips. Also provides information on the National Weather Service Heat Index Program.
- Occupational Safety and Health Administration (OSHA) working in outdoor and indoor heat environments: HRI and first aid information for workers as well as industry-specific resources and standards
- OSHA's campaign to prevent heat illness in workers: Educational resources and information on preventing heat illness in workers
- CDC National Environmental Public Health Tracking (EPHT) for climate change: Climate change-related indicators including extreme heat days and events, national heat stress hospitalization data, heat vulnerability measures, mortality data, and temperature distribution by county
- CDC Protect yourself from the dangers of extreme heat: Emergency preparedness and response pages related to extreme heat