Chewing gum can shed microplastics into saliva, study finds

Researchers at the University of California, Los Angeles (UCLA) have found that chewing gum can release hundreds to thousands of microplastics per piece into saliva, potentially to be ingested. The results of their pilot study were presented at ACS Spring 2025, held from 23–27 March in San Diego.

Scientists estimate that humans consume tens of thousands of microplastics (between 1 µm and 5 mm wide) every year through foods, drinks, plastic packaging, coatings, and production or manufacturing processes. Yet chewing gum as a potential source of microplastics hasn’t been widely studied, despite its worldwide popularity. UCLA’s Professor Sanjay Mohanty and Lisa Lowe, a graduate student in his lab, wanted to identify how many microplastics a person could potentially ingest from chewing natural and synthetic gums.

Chewing gums are made from a rubbery base, sweetener, flavourings and other ingredients. Natural gum products use a plant-based polymer, such as chicle or other tree sap, to achieve the right chewiness, while other products use synthetic rubber bases from petroleum-based polymers.

“Our initial hypothesis was that the synthetic gums would have a lot more microplastics because the base is a type of plastic,” said Lowe, who started the project as an undergraduate intern at UCLA.

The researchers tested five brands of synthetic gum and five brands of natural gum, all of which are commercially available. Mohanty said they wanted to reduce the human factor of varied chewing patterns and saliva, so they had seven pieces from each brand all chewed by one person.

In the lab, the person chewed the piece of gum for four minutes, producing samples of saliva every 30 seconds, then a final mouth rinse with clean water, all of which got combined into a single sample. In another experiment, saliva samples were collected periodically over 20 minutes to look at the release rate of microplastics from each piece of gum. Then, the researchers measured the number of microplastics present in each saliva sample. Plastic particles were either stained red and counted under a microscope or analysed by Fourier-transform infrared spectroscopy, which also provided the polymer composition.

Lowe measured an average of 100 microplastics released per gram of gum, though some individual gum pieces released as many as 600 microplastics per gram. A typical piece of gum weighs 2–6 grams, meaning a large piece of gum could release up to 3000 plastic particles. If the average person chews 160 to 180 small sticks of gum per year, the researchers estimated that could result in the ingestion of around 30,000 microplastics. If the average person consumes tens of thousands of microplastics per year, gum chewing could greatly increase the ingested amount.

“Surprisingly, both synthetic and natural gums had similar amounts of microplastics released when we chewed them,” Lowe said. They also contained the same polymers: polyolefins, polyethylene terephthalates, polyacrylamides and polystyrenes. The most abundant polymers for both types of gum were polyolefins, a group of plastics that includes polyethylene and polypropylene.

Most of the microplastics detached from gum within the first two minutes of chewing, with the act of chewing itself abrasive enough to make pieces flake off. After eight minutes of chewing, 94% of the plastic particles collected during the tests had been released. Therefore, Lowe suggests that if people want to reduce their potential exposure to microplastics from gum, they chew one piece longer instead of popping in a new one.

The study was limited to identifying microplastics 20 µm wide or larger because of the instruments and techniques used. It is therefore likely that smaller plastic particles were not detected in saliva, Mohanty said, so additional research is needed to assess the potential release of nano-sized plastics from chewing gum. He added that plastic released into saliva is a small fraction of the plastic that’s in the gum, so if used gum isn’t properly thrown away, it is yet another source of plastic pollution for the environment.

Mohanty also acknowledged that scientists don’t know for certain if microplastics are unsafe to us or not, although animal studies and studies with human cells do suggest that microplastics could cause harm. So while we wait for more definitive answers from the scientific community, individuals looking to reduce their exposure to microplastics can begin by minimising their gum consumption.

Image credit: iStock.com/Eva-Katalin