Is Chewing on Plastic Bad for Your Health?

Chewing on plastic is not harmless, even though the health effects from casual habits like gnawing a pen cap or biting a straw are subtler than you might expect. The concern is twofold: the physical act grinds plastic into tiny particles that you swallow, and the chewing process accelerates the release of chemical additives from the material into your saliva. How much risk you face depends on the type of plastic, how often and how long you chew, and whether the person doing the chewing is an adult or a small child with a still-developing body.

How Chewing Grinds Plastic Into Microparticles

When you repeatedly compress and grind a piece of plastic between your teeth, you physically break it down. Researchers have developed methods to measure the rate at which mechanical stress, including chewing, generates microplastic particles throughout a product’s life cycle.¹ Your teeth exert surprisingly strong forces, and plastics that seem solid under gentle handling can shed fragments, fibers, and microscopic particles under the repetitive shear of biting and grinding. These particles range from visible flecks down to sizes too small to see, entering the category broadly labeled microplastics and nanoplastics.

Most of these particles end up being swallowed. That matters because they carry with them whatever chemical additives were blended into the plastic during manufacturing, and because the particles themselves can interact with tissues along the entire digestive tract. The mouth is the first point of contact, but it is far from the last.

Chemicals That Leach Into Your Saliva

Plastic is rarely just a polymer. Manufacturers add plasticizers to make it flexible, stabilizers to prevent degradation, flame retardants, colorants, and other processing aids. These additives are not always chemically locked into the polymer matrix, which means they can migrate out, especially when exposed to warmth, moisture, and mechanical stress. Saliva provides all three.²

Bisphenol A, commonly called BPA, is one of the most studied leachable chemicals. Research on materials used inside the mouth found that among 13 different intraoral products tested, only a silicone baby bottle nipple released a measurable amount of BPA, about 20 micrograms, and that leaching occurred after three days of contact with artificial saliva and then stopped.³ That sounds reassuring until you consider two things: not all plastics were tested, and not all harmful chemicals are BPA. Dental aligners made from certain plastics, for instance, showed a burst of BPA release within the first hour of use, with levels dropping sharply over the following week.⁴

The mouth turns out to be a particularly efficient gateway for some of these chemicals. A study measuring BPA absorption found that dietary exposure through the mouth led to roughly three times higher bioavailability compared to bypassing the mouth entirely. The researchers highlighted a dual absorption mechanism: chemicals entering through the lining of the cheeks and gums (buccal absorption) as well as through the stomach and intestines afterward.⁵ In practical terms, holding a piece of plastic in your mouth and chewing it may expose you to higher effective doses of certain contaminants than if you simply ate the same amount of the chemical in food, because the soft tissue of your mouth is absorbing some of it directly into the bloodstream before your liver gets a chance to filter it.

Beyond BPA, phthalates are another family of concern. These are plasticizers used widely in soft, flexible plastics. Phthalates act as endocrine disruptors, and biomonitoring studies have linked food-associated phthalate exposure to oxidative damage affecting DNA, lipids, and proteins. Researchers have found that the risk curve is steepest at low-to-moderate exposures, which means even modest, everyday contact adds up.⁶ While most of the phthalate data comes from dietary exposure broadly, chewing on phthalate-containing plastics represents a direct, concentrated route. Reviews of human exposure to plastic additives including phthalates, BPA, and brominated flame retardants have flagged reproductive and developmental toxicity as the primary concerns, though human data remain limited compared with the large body of animal evidence.⁷

When microplastics are swallowed and pass through simulated human digestion, additional compounds leach out, including plasticizers and monomers that could accumulate in digestive organs and cause toxic effects.⁸ So even after the plastic leaves your mouth, the chemical release continues as it moves through your digestive system.

What Plastic Particles Do Inside Your Mouth

The mouth is not just a passageway. It has its own complex ecosystem of bacteria, fungi, and soft tissue, and microplastic particles appear to interact with all of them. Research has found that microplastics can integrate into dental plaque, alter its structure, and influence the behavior of the microbial communities living there. This includes changes to bacterial virulence, the sticky matrix that holds plaque together, and even horizontal gene transfer between microbes. These shifts raise concerns that plastic exposure could worsen the conditions that lead to cavities and gum disease.⁹

At the cellular level, the effects look more alarming. Laboratory experiments have shown that microplastics made from polymethyl methacrylate, a common dental material, are toxic to several types of oral cells, including the cells that line the inside of your cheeks and the cells that anchor your teeth in place. The particles triggered inflammation and a form of programmed cell death linked to mitochondrial stress.¹⁰ Separately, polyethylene microplastics, a type found in actual human dental calculus, reduced gum cell viability, increased cell death, and ramped up inflammatory signaling in a dose-dependent way.¹¹ These are lab experiments, not clinical trials in living people, so translating exact risk levels to your mouth is premature. But the direction of the findings is consistent: microplastic particles are not inert once they contact oral tissue.

There is also a mechanical side to the habit. Repetitive chewing behaviors, including chewing on non-food objects, have been linked to temporomandibular joint problems. A study comparing people with painful jaw clicking to those without found that the group with painful clicking reported far higher rates of oral habits like nail biting and chewing on objects, with significantly higher scores on assessments of parafunctional (non-eating) jaw activity.¹² Chewing on hard plastic pen caps or bottle caps puts your jaw through repetitive stress it was not designed for, and over time that can contribute to soreness, clicking, and dysfunction in the joint.

From Your Mouth to Your Gut

Most of the microplastic particles generated by chewing end up in your gastrointestinal tract. Research in mice has shown that polystyrene microplastics reduced intestinal mucus secretion and damaged the gut’s barrier function, the tight seal that normally keeps gut contents from leaking into the body. The same study found significant shifts in the composition of gut bacteria, with certain beneficial groups declining and overall microbial diversity changing after exposure.¹³

Broader reviews have reinforced these findings, concluding that microplastics accumulate in the gastrointestinal tract and disrupt the gut microbiome, creating an imbalance between beneficial and harmful bacteria.¹⁴ This kind of disruption has been linked in other research contexts to inflammation, metabolic problems, and impaired immune function. The gut-brain axis is also a subject of emerging interest: microplastics that promote gut inflammation and microbial imbalance may have downstream effects on neurological function, though this area remains early-stage and mostly based on animal models.¹⁵

Everyone ingests some microplastics from food, water, and air. The question with chewing plastic is whether you are adding a concentrated, repeated dose on top of that baseline. A person who chews a pen cap for an hour a day is likely generating and swallowing far more particles than they would get from, say, drinking tap water. The research is not advanced enough to put precise numbers on the added risk from this specific habit, but the mechanisms, particle generation, chemical leaching, and direct tissue contact, all point in the same direction.

Why the Risks Are Higher for Children

Young children chew on plastic constantly. Teethers, pacifiers, toy figurines, sippy cup spouts: the oral exploration of objects is a normal developmental behavior, but it means children face disproportionate exposure relative to their body weight. Testing of infant teether toys has identified hazardous chemical substances that migrate into simulated saliva, with substances detected at rates as high as 76% across samples and migration levels varying based on the properties of both the chemical and the plastic.¹⁶ A separate study using non-targeted screening found 28 distinct substances in just 10 teether samples, including phenol and cyclohexanone, chemicals with known toxicity.¹⁷

Silicone-containing children’s products marketed in China were found to contain methylsiloxanes at notable concentrations, with these chemicals detectable in saliva leachate from the products.¹⁸ The concern is not that any single teething session delivers a dangerous dose, but that daily, prolonged mouthing over months creates chronic low-level exposure during a period when organ systems are still developing.

Reviews of microplastic exposure during early development have underscored that even low doses may produce long-term health effects that show up later in life.¹⁹ Infants and young children face exposure through multiple routes simultaneously, including the placenta, breastfeeding, formula, and daily contact with toys and textiles. Because their immune and metabolic systems are still maturing, they may be more susceptible to the effects of microplastic particles and the chemicals riding along with them.²⁰

Which Plastics Are People Actually Chewing?

Adults tend to chew on pen caps, drinking straws, bottle caps, the corners of credit cards, and the tips of phone cases. These items are made from a wide variety of polymers, each with its own additive profile. Polypropylene pen caps are different from polyethylene bottle caps, which are different from polycarbonate phone cases. Some contain BPA, some contain phthalates, some contain neither but include other additives that have received less scrutiny. The hard, brittle plastics tend to shed larger fragments, while soft, flexible plastics are more likely to contain high concentrations of plasticizers.

Children, as noted, chew on teethers, pacifiers, and toys. Regulations around children’s products vary by country. In the European Union, phthalates in certain children’s toys are restricted. In the United States, the Consumer Product Safety Improvement Act limits several phthalates in children’s toys and childcare articles. But regulations tend to target known chemicals one at a time, and the non-targeted screening studies mentioned above keep finding substances that are not yet on anyone’s watch list. The regulatory framework is inevitably playing catch-up with the actual chemistry of these products.

People who wear clear dental aligners or retainers are in a slightly different category. These are medical devices designed for extended oral contact, and they undergo more testing than a random pen cap. Still, BPA release from certain aligner materials has been documented, particularly in the first hours of use.⁴ If you also clench or grind your teeth while wearing aligners, you are adding mechanical degradation on top of the chemical leaching that occurs from saliva contact alone.

Practical Ways to Reduce Your Exposure

If you chew on plastic out of habit, the most effective change is simply stopping. That advice is easier to give than to follow, since the behavior is often unconscious and stress-driven. Fidget tools made from materials like stainless steel, wood, or food-grade silicone rated for sustained oral contact may serve as substitutes, though even silicone carries some additive load. Chewing gum is another common redirect, with the trade-off that most gum bases are themselves synthetic polymers, though ones specifically designed and tested for oral use.

For children, the key is choosing teethers and toys from manufacturers that comply with the strictest available standards. Look for products that have been tested for migration of chemicals under simulated oral conditions, not just tested for the presence of a few banned substances. Replacing worn or damaged teethers regularly helps too, since surface degradation accelerates chemical release. Washing teethers frequently and avoiding exposing them to heat (which accelerates leaching) are practical steps.

For anyone wearing dental aligners or retainers, rinsing them thoroughly before the first use and avoiding chewing or clenching on them beyond what is necessary for fit can reduce both chemical and microplastic exposure. Some manufacturers recommend soaking aligners before first use, and the data on initial BPA release supports that practice.

The Gap Between Animal Data and Human Certainty

Honest assessment of this topic requires acknowledging a frustrating gap. The cell and animal studies are genuinely worrying: oral cells die, gut barriers weaken, microbial communities shift, inflammatory pathways activate. But most of these experiments use higher concentrations than a typical person would encounter from casual chewing, and animal digestive systems differ from human ones in ways that affect how particles behave. Long-term human studies tracking health outcomes specifically from plastic-chewing habits essentially do not exist.

What we do have is mounting evidence that microplastics are accumulating in human tissues, that the chemicals they carry are biologically active at low doses, and that the mouth provides an unusually direct absorption route. The precautionary logic is straightforward: you are generating particles and releasing chemicals in a part of your body designed to absorb things efficiently, and the substances involved have documented biological effects in every system that has been studied carefully. Whether the dose from chewing a pen cap for 20 minutes matters on its own is unknown. Whether the cumulative exposure from years of the habit, layered on top of all the other microplastic sources in modern life, pushes you past a threshold is the question researchers are still trying to answer.