The start of spring is just around the corner. And with it, comes questions about whether your sneezing and wheezing could be due to COVID-19 or allergies. But a new study has a surprising conclusion: Allergy season may actually increase your risk of contracting COVID-19.
The study, which was published in Proceedings of the National Academy of Sciences, used data on airborne pollen concentrations, humidity, temperatures, COVID-19 infection rates and lockdown scenarios from 130 sites in 31 countries across five continents. After analyzing the data, the researchers discovered that higher pollen levels were linked to an extra 10 to 30 percent increase in the infection rate of SARS-CoV-2, the virus that causes COVID-19.
The scientists also found that, on average, COVID-19 infection rates increased after there were higher concentrations of pollen in the air. The rise in cases usually happened four days after the pollen increase.
The team decided to conduct the study after publishing research that found pollen interferes with the body's immune response to other airway viruses, like rhinovirus and RSV, both of which cause the common cold, study co-author Dr. Stefanie Gilles, chair of environmental medicine at the Technical University of Munich, tells Yahoo Life. The researchers then "saw the SARS-CoV-2 infection rates rise on the entire Northern hemisphere, during a period in March with very warm and dry weather and with a lot of pollen all over Europe and Northern America," and decided to take a closer look, she says.
"It made sense, as COVID is a respiratory virus, to look at pollen interactions," study co-author Dr. Lewis Ziska, associate professor of environmental health sciences at the Columbia University Irving Medical Center, tells Yahoo Life
The big question, though, is why there might be a link.
While the study didn't determine that, the researchers have some theories. One is that allergy season naturally causes people to sneeze and cough more. "When you're sneezing and coughing, you're spreading more bodily fluids around," study co-author Dr. Leonard Bielory, an allergy specialist at Rutgers University–New Brunswick, tells Yahoo Life. "If someone is infected with COVID-19 and is sneezing and coughing, that may cause others around them to become infected, too."
Pollen also releases substances that diminish the ability of nasal cells to fend off viruses, Gilles says. The result, she says, is that "viruses can replicate more easily in the nose." And, when viruses replicate, they can make you sick. There are even other environmental factors that can increase the risk of infection, like humidity, which "may act in synergy with pollen" to increase your risk of getting sick, Gilles says.
One thing experts stress, though, is that the pollen itself isn't actually carrying SARS-CoV-2 and infecting people. "Pollen is not causing infections," Gilles says. "Infection is transmitted by contact with infected persons."
Inflammation may play a role, too, Dr. Purvi Parikh, an allergist and immunologist with Allergy & Asthma Network, tells Yahoo Life. "Airways that are already inflamed have a harder time clearing and fighting infections," she says, adding that people who also struggle with asthma have a particularly tough time with this.
Despite the theories, it's also possible that this is "coincidental," Dr. Richard Watkins, an infectious disease physician in Akron, Ohio, and a professor of internal medicine at the Northeast Ohio Medical University, tells Yahoo Life. Watkins points out that the findings are unusual, especially given that "being indoors increases the risk of COVID-19." Being outdoors, which people tend to do more when the weather is nice and pollen counts are high, decreases the risk, he says.
Bielory admits that more research is needed. "This is a marker and a phenomena," he says. "It has to be further studied." However, Gilles says, it's a good idea to mask up outdoors during high pollen days, whether you'll be around others or not. "This diminishes your risk to get infected—and keeps the pollen out of the airways," she says.
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