The small study comes as researchers have increasingly been discovering small shards of plastic called microplastics throughout the world, from the tops of mountains to the bottom of the ocean -- and even in the air we breathe.
They have also been discovered microplastics riddled throughout human bodies -- including inside our lungs, blood and brains -- sparking fears about the potential effect this could be having on health.
"I don't want to alarm people," Sanjay Mohanty, the lead researcher behind the new study, told AFP.
There is no evidence directly showing that microplastics are harmful to human health, said Mohanty of the University of California, Los Angeles (UCLA).
The new pilot study instead sought to illustrate yet another little-researched way that these mostly invisible plastic pieces enter our bodies -- chewing gum.
Lisa Lowe, a PhD student at UCLA, chewed seven pieces each of 10 brands of gum; Then the researchers ran a chemical analysis on her saliva.
They found that a gramme of gum (0.04 ounces) released an average of 100 microplastic fragments, though some shed more than 600. The average weight of a stick of gum is around 1.5 grammes.
People who chew around 180 pieces of gum a year could be ingesting roughly 30,000 microplastics, the researchers said.
This pales in comparison to the many other ways that humans ingest microplastics, Mohanty emphasised.
For example, other researchers estimated last year that a litre (34 fluid ounces) of water in a plastic bottle contained an average of 240,000 microplastics.
- 'Tyres, plastic bags and bottles' -
The most common chewing gum sold in supermarkets is called synthetic gum, which contains petroleum-based polymers to get that chewy effect, the researchers said.
However packaging does not list any plastics in the ingredients, simply using the words "gum-based".
"Nobody will tell you the ingredients," Mohanty said.
The researchers tested five brands of synthetic gum and five of natural gum, which use plant-based polymers such as tree sap.
"It was surprising that we found microplastics were abundant in both," Lowe told AFP.
The gum shed almost all of the microplastics during the first eight minutes of chewing, she added.
David Jones, a researcher at the UK's University of Portsmouth not involved in the study, told AFP that manufacturers should be forced to give more specific ingredients than just "gum-based".
Jones said he was surprised that the researchers found certain plastics not known to be in gum, suggesting they could have possibly come from another source.
But the overall findings were "not at all surprising", he added.
People tend to "freak out a little bit" when told that the building blocks of chewing gum were similar to what is found "in car tyres, plastic bags and bottles", Jones said.
Lowe also warned about the plastic pollution from chewing gum -- particularly when people "spit it out onto the sidewalk".
The study, which has been submitted to a peer-reviewed journal but not yet published, was presented at a meeting of the American Chemical Society in San Diego.
The world's biggest chewing gum manufacturer, Wrigley, did not respond to AFP's request for comment.
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