Unhoused Californians Face 38% Higher ER Risk for Heat Illness, Yet Are Nearly Invisible in the Data

For Immediate Release: Media Advisory
Contact: Renate Myles/Katie Mullan

What:

New analysis of heat-related health surveillance data in California collected from 2005-2024 found that the people bearing the greatest burden of heat-related illness are often missing from the data entirely. Using 2019 and 2020 data, the period for which heat-related Emergency Room (ER) visits could be linked to housing status, researchers found that 1 in 10 heat-related ER visits in California involved unhoused individuals. On days with extreme heat, there was a 38% higher risk of an ER visit for heat-related illness among unhoused individuals in California compared to the general population. The heat-related data is part of broader environmental health data collected and analyzed by Tracking California, an independent environmental public health surveillance and research program at the Public Health Institute.

“The missing data matters because data informs prevention measures,” said Shubhayu Saha, Ph.D., Executive Director of Tracking California. “This problem is not only relevant for unhoused individuals. Community clinics and safety-net providers, the health systems that serve low-income, uninsured and undocumented Californians, are largely absent from the surveillance data. Data informs exactly where prevention actions, from expanded social services and outreach to cooling centers and resilience hubs, are needed most.”

Dr. Saha urges health systems that need support and guidance in reporting this data to contact Tracking California. Better health tracking informs state heat-resilience investments to prevent heat-related illness and deaths.

Additional findings:

• Rates of heat-related hospitalizations and emergency room visits have increased by roughly 30% between the first decade (2005-2014) and the most recent decade (2015-2024) of data.
• Highly populated counties have larger number of recorded heat-related emergency room visits across all populations. Los Angeles, Riverside, San Bernardino, San Diego and Kern counties had the largest number of cases between 2015-2024.
• Rates of heat-related emergency room visits continue to worsen across inland and rural areas from Imperial County through the Central Valley and into Northern California. Imperial, Plumas, Amador, Tehama and Modoc counties had the highest rates between 2015-2024.
• Black Californians experience the highest overall rates of heat-related illness across all race and ethnic groups, and the differences are most pronounced in agricultural counties.
• March of this year was California’s warmest and driest in more than 130 years, shattering temperature records from San Francisco to Los Angeles to the Coachella Valley.

Who:

These experts are available to speak to reporters upon request:

• Shubhayu Saha, Ph.D., Executive Director of Tracking California, a program of the Public Health Institute, is available to speak to reporters upon request.
• Jhaqueline Valle Palominos, M.P.H., Health Surveillance Lead, Tracking California

Data Briefs:

• Invisible Patients, Part 1: Who’s Missing from California’s Health Data? June 2026 Data Brief
• Invisible Patients, Part 2: Tracking the Impact of Heat on Unhoused Californians, June 2026 Data Brief
• Invisible Patients, Part 3: Extreme Heat Days Hit Unhoused Californians Hardest, June 2026 Data Brief

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Tracking California is an independent environmental public health surveillance and research program at the Public Health Institute. For nearly 25 years, Tracking California has collected, analyzed, and made publicly available data on the health effects of environmental exposures across California. The program is committed to community based participatory research. For information, visit www.trackingcalifornia.org.

The Public Health Institute is a national independent nonprofit that advances the health and wellbeing of all people and communities, particularly those facing the greatest barriers. Rooted in 60 years of public health experience, PHI moves ideas into action through practice, policy, research and community engagement, while serving as the operational backbone for more than 40 programs delivering evidence-based solutions to complex health challenges. For more information, visit www.phi.org.