At the turn of the 20th century, William Wrigley Jr. was bent on building an empire of gum, and as part of his extensive hustle, he managed to persuade the U.S. Department of War to include his products in soldiers’ rations. His argument—baseless at the time—was that chewing gum had miraculous abilities to quench thirst, stave off hunger, and dissipate nervous tension. But he was right: Scientists have since found that gum chewing can indeed increase concentration, reduce the impulse to snack, alleviate thirst, and improve oral health.
Perhaps that’s why people around the world have had the impulse to gnaw on tacky materials—roots, resins, twigs, blubber, tar made by burning birch bark—for at least 8,000 years. Today, gum is again being marketed as a panacea for wellness. You can buy gum designed to deliver energy, nutrition, stress relief, or joint health; scientists are even developing gums that can protect against influenza, herpes, and COVID. Ironically, this new era of chewing gum is manufactured with a distinctly modern ingredient, one not usually associated with wellness: plastic. 
By the time Wrigley began his business venture, Americans had grown accustomed to chewing gum sold as candy-coated balls or packaged sticks. The base of these chewing gums was made from natural substances such as spruce resin and chicle, a natural latex that Aztecs and Mayans chewed for hundreds if not thousands of years. Unfortunately for 20th-century Americans, the chicozapote trees that exude chicle take a long time to grow, and if they are overtapped, they die. Plus, cultivated trees don’t produce nearly as much chicle as wild trees, says Jennifer Mathews, an anthropology professor at Trinity University and the author of Chicle. In the 1950s, chicle harvesters began struggling to meet demand. So gum companies turned to the newest innovations in materials science: synthetic rubbers and plastics.
Today, most companies’ gum base is a proprietary blend of synthetic and natural ingredients: If a packet lists “gum base” as an ingredient, that gum most likely contains synthetic polymers. The FDA allows gum base to contain any of dozens of approved food-grade materials—substances deemed either safe for human consumption or safe to be in contact with food. Many, though, are not substances that people would otherwise think to put in their mouth. They include polyethylene (the most common type of plastic, used in plastic bags and milk jugs), polyvinyl acetate (a plastic also found in glue), and styrene-butadiene rubber (commonly used in car tires). The typical gum base contains two to four types of synthetic plastics or rubbers, Gwendolyn Graff, a confectionery consultant, told me.
Everything we love about gum today is thanks to synthetic polymers, Graff said. Polyvinyl acetate, for example, strengthens the bubble film. “If you blow a bubble, and it starts to get holes in it and deflate, that’s usually an indicator that it doesn’t have polyvinyl acetate,” Graff said. Styrene-butadiene rubber creates a bouncy chewiness that makes gum more likely to stick to itself rather than to surfaces like your teeth. Polyethylene can be used to soften gum so it doesn’t tire out your jaw. Gums with only natural polymers “can feel like they’re going to fall apart in your mouth,” Graff said.
Plastic gum, though, also falls apart, in a way: Gum chewing has been linked to microplastic ingestion. In a study published in December, U.K. researchers had a volunteer chew on a piece of gum for an hour, spitting into test tubes as they went. After an hour of gum chewing, the saliva collected contained more than 250,000 pieces of micro and nano plastics—comparable to the level of microplastics found in a liter of bottled water. In a study presented at a recent meeting of the American Chemical Society (which has not yet been peer-reviewed), a graduate student’s saliva contained elevated microplastic levels after she chewed several commercially available gums, including natural ones. The research on gum chewing and microplastics is still limited—these two papers effectively represent analysis of just two people’s post-chew saliva—but gum chewing has also been correlated with higher urine levels of phthalates, plastic-softening chemicals that are known endocrine disruptors.
Scientists are still learning about the health impacts of microplastic ingestion, too. Microplastics find their way into all kinds of foods from packaging or contamination during manufacturing, or because the plants and animals we eat absorb and ingest microplastics themselves. As a result, microplastics have been found in human livers, kidneys, brains, lungs, intestines, placentas, and breast milk, but exactly how our bodies absorb, disperse, and excrete ingested plastic is not very well studied, says Marcus Garcia, who researches the health effects of environmental contaminants at the University of New Mexico. Some research in mice and cultured cells hint that microplastics have the potential to cause damage, and epidemiological research suggests that microplastics are associated with respiratory, digestive, and reproductive issues, as well as colon and lung cancer. But scientists are still trying to understand whether or how microplastics cause disease, which microplastics are most dangerous to human health, and how much microplastic the body can take before seeing any negative effects.
The answer could affect the future of what we choose to eat—or chew. Ingesting tiny plastic particles might seem inevitable, but over the past 10 years or so, Americans have grown understandably fearful about bits of plastic making their way into our food, fretting about microwaving food in plastic containers and drinking from plastic bottles. Gum has, for the most part, not triggered those worries, but in recent years, its popularity had been dropping for other reasons. In a bid to reverse that trend, gum companies are marketing synthetic gum as a tool for wellness. Just like Wrigley, they are betting that Americans will believe in the power of gum to soothe nerves and heal ailments, and that they won’t think too hard about what modern gum really is. For anyone worried about swallowing still more plastic, after all, gum is easy enough to avoid.
