What does hayfever have to do with domestic violence? Quite a lot, according to research.
A study recently published in the Journal of Health Economics found that reports of violent crime decline by approximately 4 percent on days where the local pollen hunt is low. The team also found there is a particularly noticeable drop—4.4 percent—in violent crimes that take place in the home—a fact that surprised researchers.
Previous studies have shown that situational circumstances (like an unseasonably hot day) can affect the likelihood of a crime taking place—or at the very least, being reported. The idea here is that it affects the balance between the drawbacks of committing a crime and the benefits of a crime, which combined create the net cost of criminal activity.
If the drawbacks outweigh the benefits, it is less likely the crime will take place.
For the study, researchers wanted to look at the net cost of criminal activity that comes with a common health shock—in this case, seasonal allergies, which affects up to one in five Americans. Allergies can cause nasal congestion, watery eyes, an irritated throat and sneezing. They can also affect cognitive ability, mood and sleep activity.
"We started this research with the personal experience that allergies made us feel less physically active and slugging on high pollen days," co-author Shooshan Danagoulian, an assistant professor in the department of economics at Wayne State University, told Newsweek.
"Past research has shown that high pollen reduces children's performance on math and English tests, so we expected to see some effect on other activities as well. Though our findings confirmed our suspicions, we did not expect the magnitude of the effect on crime—the 4 percent decline in violent crime is very substantial."
Danagoulian and colleagues started by taking pollen count data from 15 U.S. cities, including Atlanta, Baltimore, Colorado Springs, Detroit and Kansas City, and comparing it to crime rates. The 4 percent drop in reported crimes calculated might not sound like a great deal—but it is equivalent to what you might see if the city's police force increased by 10 percent or if the prison population increased by 20 percent, the researchers say.
Interestingly, one day with an unusually high pollen count had effects that carried over into subsequent days. The researchers found that on weeks with average pollen levels bar one day with exceptionally high pollen counts, the overall number of crimes reported fell 11 percent.
Why this might be is uncertain. "It could be that people feel sick on high pollen days, or they may forgo alcohol when they are suffering from allergies, etcetera," said Danagoulian.
The reasons for the drop in domestic crimes reported is also unclear. If anything, a greater number of people indoors would predict higher rates of domestic crimes, making the decline even more significant.
"This implies that the risk of residential violence, which is predominantly domestic assault or family violence, is even more sensitive to transitory health shocks than the previous analysis suggests," the study authors write.
"Our research gives law enforcement and local governments a better understanding of the nature of interpersonal violence, especially violence at home," Danagoulian said. "Domestic violence is a particularly difficult problem for law enforcement to solve since they cannot patrol inside people's homes, and our research sheds light on the role of health in the moment on such violence."
It also highlights how responsive violence is to situational factors, says co-author Monica Deza, an assistant professor of Economics at City University of New York (CUNY) Hunter College. Seasonal allergies are just one piece the puzzle.
"Previous literature find that domestic violence increases following an upset football loss," Deza said in a statement emailed to Newsweek. "A policy implication is that some of these violent incidents could be prevented if individuals knew how to manage their anger better and were able to not respond with violence with such immediacy."
Meanwhile, seasonal allergies could affect more than just crime rates. The team now plans to explore how pollen counts affect car safety.