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How a warmer winter can affect your health

Jan 22, 2020
View of IUPUI's Wood Fountain in the winter
IUPUI’s Wood Fountain was surrounded by grass, not snow, most days in January.Photo by Liz Kaye, Indiana University

After a record-cold winter in 2018-19, Indiana is currently experiencing unseasonably warm weather for this time of year.

According to data from the National Weather Service, the average monthly temperature in Indianapolis in December was 5.4 degrees above normal, and the average monthly temperature in January – as of Jan. 21 – is 7.6 degrees above normal, with some daily averages reaching 22 degrees above normal.

While the weather outside feels less frightful, the health effects of a warmer-than-average winter might not be so pleasant. We talked to Indiana University School of Medicine’s Bill Sullivan, Showalter Professor of Pharmacology and Toxicology and professor of microbiology and immunology, about what to look out for and how to protect your health after a mild winter. Read on to see his answers.

Question: How do cold temperatures during the winter season affect human health?

Bill Sullivan: People usually associate viral illnesses with the cold temperatures of winter; flu season, for example, peaks between December and March, and we even refer to rhinoviruses as “colds.”

While we know that the cold air itself is not the direct cause of the sniffles, it might have an indirect effect by allowing some viruses to survive a bit longer outside the body. The cold outside also means that we stay indoors more often, which could facilitate the spread of germs if sick people are in proximity.

In other words, bundling up to stay warm is not going to stop you from catching a cold or flu virus someone gave you from a handshake or cough. To avoid getting sick in winter, your best bet is to get the flu vaccine, sanitize your hands and encourage people who are ill to stay home so they don’t spread their germs. Don’t underestimate the flu – it kills tens of thousands of people each year in the United States.

Q: In Indiana, even with the recent cold snap, ice and snow have been noticeably less prevalent this season. When winters are warmer than average, what does this mean for the bacteria, viruses and other things in our environment that can make us sick?

Sullivan: Viruses are still going to be contagious no matter what the season; for example, people still get colds in the summer. The cold air only gives the virus a slightly better chance at hopping from one person to another.

One thing we had to worry about this year was flooding, because it hasn’t been cold enough for the rain to become snow. Not only can flooding cause accidents, but water in homes is a breeding ground for mold, which can make asthma worse or cause respiratory illnesses like pneumonia.

The warmer weather is also likely to make pollen allergies especially rough this spring. Plants and trees rely on temperature cues to release pollen, so climate change throws off their schedule, which means allergy season could come sooner and last longer. In terms of health, allergies mixed with the pollution in the air can irritate and weaken our lungs, making us more prone to catch serious respiratory illnesses.

Q: What about diseases carried by insects?

Sullivan: The biggest issue with warmer weather is that we see increased migration and prolonged survival of insects that carry really nasty diseases. Ticks spread bacterial species that cause diseases like Lyme disease, Rocky Mountain spotted fever and ehrlichiosis. Mosquitoes carry viruses like the West Nile virus and Eastern equine encephalitis.

If we go farther south, there’s an increasing risk of tropical diseases entering the United States due to climate change. As temperatures get warmer, our country is becoming more hospitable to these disease-carrying insects. One example of this is Chagas disease, which is caused by a single-celled parasite called Trypanosoma cruzi. It is carried by “kissing bugs” that have now invaded the southern regions of the U.S. It’s a pretty disgusting process – these bugs bite you on the face while you sleep, and while they suck your blood they poop on your face. You then scratch the bug bite and rub the parasite-laden poop into the wound. At the moment, it is still rare to get Chagas disease – which can lead to life-threatening heart and gastrointestinal problems – in the U.S., but the kissing bugs that transmit the parasite are moving in because of climate change.

Another parasite we normally don’t see in the U.S. is Leishmania, which is carried by sand flies. But in recent years, cases of cutaneous leishmaniasis, which causes disfiguring skin ulcers, have been reported in Texas and Oklahoma.

The U.S. has long enjoyed immunity to these tropical diseases, which can be very difficult to treat, and it is alarming to see them surfacing here. Some have speculated that climate change could potentially bring other mosquito-borne diseases to the U.S. too, including the yellow fever virus and the Plasmodium parasite, which causes malaria.

Q: After a mild winter, is there anything that people can do differently to protect their health?

Sullivan: The freezing winters tend to better control the insect population, including disease-carrying ticks. The cold doesn’t necessarily kill the ticks themselves, but it can keep the numbers of deer and mice down, which are hosts the ticks need to expand their numbers. Milder winters typically lead to an explosion of the tick population in spring and summer. So people should be more vigilant for ticks: cover exposed skin and wear hats when hiking or going into tick-infested areas, and be sure to promptly check your body and your kids’ bodies for ticks after being outdoors. Some say that spraying clothes with the insecticide permethrin keeps ticks away.

Mosquitoes are also likely to thrive. To reduce your chances of catching West Nile or Eastern equine encephalitis, apply a mosquito repellent with DEET. Remember, there is no cure or vaccine for these viral infections, so prevention is key.

Finally, to help prepare for what is likely to be a rough hay fever season, start your allergy meds a little early – before symptoms kick in.

Q: On the other hand, are there any health benefits of having a warmer winter?

Sullivan: Well, I don’t think too many people are missing icy roads or sore muscles from shoveling snow! But this is dwarfed by the magnitude of the dangers climate change is bringing across the globe.

What many people don’t realize is that climate change does not mean warmer winters every year. It means drastic swings in weather patterns as the average temperature of the world increases. This winter may be unusually mild, but remember the last few years have been devastatingly cold. These extremes are only going to get more pronounced unless we start taking steps to mitigate the damage we’re doing to the planet through pollution. Getting rid of the pollution will help us all breathe a little better, and knowing that we are preserving our planet for future generations should help us all sleep a little better, too.


IU Newsroom

Andrea Zeek

Senior Communications Consultant

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