The risk of being bitten by a dog is higher on hot, sunny, and smoggy days, new research suggests

• A new study from Harvard analyzed almost 70,000 reports of dogs biting humans in the US.
• The study showed that incidents of dogs biting humans increased in line with rising temperatures.
• It also increased with higher UV levels and on days when certain types of pollution were high.

Dogs can be more aggressive on hot, sunny, and smoggy days, according to a new study that analyzed almost 70,000 US reports of dogs biting humans.  

The records were sourced in eight US cities — Dallas, Houston, Baltimore, Baton Rouge, Chicago, Louisville, New York City, and Los Angeles — between the years 2009 and 2018, and cross-checked with data on pollution and weather over that same period.

The research, led by Harvard Medical School scholars, found there were more reports of dog bites on days with higher temperatures, as well as days with higher UV and pollution levels. 

On days with higher UV, dog bites increased by 11%, and higher temperatures caused a 4% increase. Higher ozone, a common pollutant, was responsible for a 3% rise in dog bites.

The researchers drew the conclusion that "the societal burden of extreme heat and air pollution also includes the costs of animal aggression."

Conversely, the researchers found there was no change when dogs were exposed to increased levels of PM2.5, another type of polluting particle that was measured.

The findings corroborate other research linking aggressive behavior in animals and humans with environmental factors.

A  2019 study on the effect of short-term exposure to air pollution on aggressive behavior in the US suggested that a policy that reduces air pollution across the US by only 10% could result in up to $1 billion of savings in crime costs by reducing assaults. 

The study had several limitations, and it's unclear if the results also had to do with the way humans react around dogs in hot weather. 

It only analyzed severe dog bites and excluded all accidents that didn't required medical treatment or hospitalization.

It also didn't account for other potential determining factors, like "breed, sex, castration/spaying status." The study also didn't address "bite severity, victim age, gender, familiarity with dog and the interactions leading up to the dog bite," as this more specific information wasn't included in public records.