By Christina Hernandez Sherwood

An illustration of the sun’s rays hitting the earth and bouncing off of the earth and atmosphere to depict global warming

About a dozen years ago, Misha Rosenbach, MD, the Paul R. Gross Professor of Dermatology in the Perelman School of Medicine, noticed a spate of adult patients coming to the hospital with hand, foot, and mouth disease, which causes telltale sores in the mouth and a rash on the hands and feet. The virus is a scourge for the daycare set, but was unusual among adults.

“It was a little uncommon to have these clusters of otherwise healthy-appearing adults having pretty severe hand, foot, and mouth disease,” said Rosenbach. He soon presented the findings in the Infectious Disease Division’s clinical case conference. Afterward, another doctor approached Rosenbach with a theory: Perhaps the rise in cases was related to the region’s increasingly mild winters. It had been predicted, Rosenbach said, that changing weather patterns would impact viral disease spread.

A scan of hand, foot, and mouth disease data in China, where the virus is a reportable illness, confirmed that diagnoses increased during hot and humid periods. “When you start looking into it,” Rosenbach said, “there are a lot of [dermatological conditions that are affected by the changing climate].”

Misha Rosenbach, MD
Misha Rosenbach, MD

The findings inspired a 2017 paper in the Journal of the American Academy of Dermatology, co-authored by Rosenbach, that described how several North American diseases, including hand, foot, and mouth disease, Lyme disease, and Zika virus could expand their geographic footprint or cause longer, more intense seasons of illness due to climate change. Those predictions were since borne out for Lyme and Zika, and also proved true for certain fungal and parasitic infections.

“Climate touches everything, and the skin is a big environmental interface organ, so it’s not surprising that there is a relationship between them,” Rosenbach said. “This is an area of medicine that’s just starting to be explored.”

Penn Medicine researchers like Rosenbach are adding to a growing body of evidence showing the many ways climate change touches human health. Their work elucidates how the climate affects skin conditions, cardiovascular events, maternal health, and even the effectiveness of medications. This research represents a key component of Penn Medicine’s mission as a health care organization: to improve well-being not only for individual patients, but for the community at large.

People and planet are ‘inextricably linked’ 

It was the Pacific Northwest heat wave of 2021, which caused hundreds of deaths in the region, that opened the eyes of Sameed Khatana, MD, MPH, an assistant professor of Cardiovascular Medicine in the Perelman School of Medicine. “It’s not an area that traditionally we associate with extreme heat,” he said. “When these communities are now being exposed to extreme heat, you’re starting to see a greater impact on the health of the populations there.”

When we get overheated, mechanisms in our bodies work hard to release excess heat, Khatana said. This effort causes the heart to beat faster and harder—a strain that can make certain people susceptible to a heart attack or other cardiovascular event. In fact, as Khatana outlined in an October 2023 paper in the journal Circulation, because of climate change, heat-related cardiovascular deaths would be predicted to increase in the United States over the next four decades, with older adults and Black adults experiencing the greatest impact. (Black adults already have a higher risk of cardiovascular disease, which can be tied to both social determinants of health and clinical factors like high blood pressure.)

Health care providers should consider counseling patients with pre-existing conditions—or those with jobs that expose them to high temperatures, such as construction or agricultural workers—to recognize symptoms of heat exposure, Khatana said. Leaders of health systems should think about how they’ll respond to a community heat wave, he said, perhaps by setting up cooling tents near the emergency department and increasing staff.

“What happens to the environment impacts our health,” Khatana said. “The health of the planet and the health of the individuals living on the planet are inextricably linked.”

Climate change can even disrupt sleep. An observational study published in Sleep Health by researchers from the Perelman School of Medicine and the University of Louisville found that a warm bedroom, air pollution, and high levels of carbon dioxide were all independently linked to lower sleep efficiency, the time spent sleeping relative to the time available for sleep.

“These findings highlight the importance of the bedroom environment for high-quality sleep,” said study lead author Mathias Basner, MD, PhD, a professor and director of the division of Sleep and Chronobiology in Psychiatry at Penn Medicine.

While certain medications are known make people more susceptible to high temperatures, Sean Hennessy, PharmD, PhD, a professor in the Department of Biostatistics, Epidemiology and Informatics in the Perelman School of Medicine, has identified one drug that appears to have a protective effect.

Statins, which are taken to lower cholesterol levels, also improve the body’s ability to dilate blood vessels in the skin, which help release excess heat. In a 2019 paper in Scientific Reports, Hennessy quantified the connection, showing that statin use had a stronger effect on survival during hot weather than milder temperatures. While the benefit needs more study, he said the research shows that it’s particularly important for people who use statins to remember to take the medication when it’s hot out.

In related work, Hennessey also found that patients taking diuretics can reduce their risk of death by taking prescription potassium supplements during hot weather. “Climate change is probably the largest threat to human health in the 21st century,” he said. “It’s going to affect the treatment of virtually every [medical] condition.”

A healthier world for all 

Every time there’s a flood in Philadelphia’s Eastwick neighborhood, which sits at the confluence of Cobbs and Darby Creeks in the southwestern corner of the city, locals face a deluge of water that flows first into a landfill site, then into their homes. In the aftermath, there are concerns about toxic chemicals, mold, and asthma, said Marilyn Howarth, MD, director of community engagement at the Center of Excellence in Environmental Toxicology at the Perelman School of Medicine.

“Imagine the health impacts of repeated flooding,” said Howarth, also an adjunct associate professor in the Department of Systems Pharmacology and Translational Therapeutics in the Perelman School of Medicine. “Imagine the mental health toll that takes.”

The center, funded by the National Institute of Environmental Health Sciences, researches local issues of environmental concern, including flooding, heat, and air pollution. In its years of work with the Eastwick community, the center has engaged with residents about how to safely clean up following a flood and assisted residents as they work with municipal, state, and federal agencies in developing a potential solution to the ongoing flooding.

“Usually what is good for the environment is also good for human health,” Howarth said. “Better management of stormwater through reduction of impervious ground not only improves the flooding, but creates a healthier neighborhood for all.”

Eugenia South, MD, MS
Eugenia South, MD, MS

The Urban Health Lab at the Penn Medicine Center for Health Justice houses a repository of population-level research that highlights the connection between our surroundings and what’s happening in our bodies, said Eugenia South, MD, MS, the center’s executive director and the Ralph Muller Presidential Associate Professor of Emergency Medicine in the Perelman School of Medicine.

There is research showing that people’s heart rates calm when they walk past green space, that pregnant people have better cardiovascular outcomes when they live near green space and that greenery has a positive impact on blood pressure and cortisol levels. “There are many studies that paint a convincing picture of the importance of nature and green space,” said South, who is also associate vice president of Health Justice at UPHS. “We know these things work to promote health and safety. We should be doing them.”

South and her team spearheaded Deeply Rooted, a community-academic collaborative that translates research about the benefits of nature into boots-on-the-ground action. In collaboration with over 20 community partners in West and Southwest Philadelphia, Deeply Rooted is planting trees, greening vacant lots, and building miniature parks. Deeply Rooted engages with local youth to teach the health benefits of nature and use nature as a tool to teach civic engagement and leadership. Additionally, local community residents and organizations receive grants from Penn Medicine and Children’s Hospital of Philadelphia to realize their visions for greener neighborhoods, whether by creating community gardens, organizing bike rides in nature, or completing another nature-inspired project. 

“All aspects of health, ultimately, are shaped by our environment,” South said. “The hope is that we [as researchers] can contribute to a conversation about solutions.”


Explore more coverage of sustainability at Penn Medicine 

How Penn Medicine is going green for good health: To improve health while addressing climate change, Penn Medicine is investing in major initiatives to become the most environmentally friendly health care system in the country.

Surgery and anesthesia teams address climate impacts in the OR: From anesthesia gases that have outsized greenhouse effects, to medical waste disposal, operating rooms at Penn Medicine are greening health care.

Health care teams “act locally” to support Penn Medicine sustainability goals: Teams across Penn Medicine are working hard to “think globally, act locally” when making environmentally friendly changes in their day-to-day operations.

How the next generation of physicians will combat climate change: Through a new Planetary Health curriculum, Penn medical students are learning about the impact of climate change on human health.

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