- Posted May 11, 2026
Nighttime Heat Waves Increase Asthma Risk
Extreme heat waves appear to be a trigger for asthma attacks, with nighttime heat proving particularly risky, a new study suggests.
Hospitals in Baltimore see an increase in asthma-related ER cases in the weeks following heat waves, researchers reported May 6 in the journal GeoHealth.
Looking more closely, researchers found that intense heat that stretched into the night best captured asthma risk, especially in lower-income neighborhoods.
“When it’s hot outside at night, it’s stifling in an upstairs bedroom of a row home without air conditioning,” said researcher Benjamin Zaitchik, a professor of earth and planetary science at Johns Hopkins University in Baltimore.
“I don’t think it’s overly dramatic to say there are life or death consequences, because people can have fatal asthma attacks, but it also affects quality of life, happiness and a kid’s ability to enjoy childhood,” he noted in a news release.
For the study, researchers analyzed 819 adult and 695 pediatric asthma ER visits that occurred during Baltimore summers from 2016 to 2022. The team compared those cases to daytime and nighttime temperatures in the patients’ neighborhoods.
Neighborhoods with the biggest swings in nighttime temperatures were the most likely to see increases in asthma-related ER cases, the study found.
Kids were 28% to 47% more likely to suffer a severe asthma attack following nighttime heat waves, with risk varying between neighborhoods, researchers found. Likewise, adults were 26% to 40% more likely to need ER treatment for asthma.
Prolonged to exposure to heat night after night can lead to worsening asthma symptoms, researchers said.
“Triggers of an asthma exacerbation/asthma attack may begin with an increase in symptoms, such as cough, chest tightness and shortness of breath,” said senior researcher Dr. Meredith McCormack, director of the Asthma Precision Medicine Center of Excellence at Johns Hopkins School of Medicine.
“Initially, an individual may try using their inhalers more often and other measures before coming to the emergency room,” McCormack said in a news release. “So, there may be a lag of several days before symptoms are severe enough to prompt an emergency department visit.”
Nighttime heat wears on people with asthma because their bodies don’t get a chance to rest and recover, she said.
Some of the body’s defenses also are lower at night. For example, the hormone adrenaline has a cycle that naturally dips around 3 a.m., making it less available to help the body manage asthma symptoms.
These results indicate that “Code Red” warning systems for extreme heat might not be as effective as they could be, given that they rely on daytime temperature forecasts, researchers said.
Cities also could help residents more by taking temperature readings at the neighborhood level, rather than relying on a single, citywide measurement from the local National Weather Service station, researchers said.
“Heat exposure can vary drastically from one neighborhood to the next, and those differences matter for health,” lead researcher Bianca Corpuz said in a news release. Corpuz is a visiting researcher at Johns Hopkins.
“When we measure temperature at the neighborhood scale, we can see patterns that aren’t captured by regional weather data,” she said. “That kind of local information is critical if cities want to better protect vulnerable communities.”
More information
The Allergy and Asthma Foundation of America has more on weather triggers for asthma.
SOURCES: Johns Hopkins University, news release, May 6, 2026; GeoHealth, May 6, 2026
