Invisalign aligners are not acutely toxic, but the plastic does release small amounts of chemicals and microplastic particles during normal wear. The levels detected in studies fall below established toxicity thresholds, though researchers have raised questions about cumulative exposure over treatments that can last a year or longer.
The material itself is FDA-cleared as a Class II medical device, meaning it passed biocompatibility testing before reaching the market. But “cleared” and “completely inert” are not the same thing. Here’s what the research actually shows about what comes off these aligners and into your mouth.
What Invisalign Aligners Are Made Of
Since 2013, Invisalign has used a proprietary material called SmartTrack. It’s a multi-layer thermoplastic polyurethane, a type of medical-grade plastic built from specific chemical building blocks plus additives. This replaced an older polyurethane material and was designed to deliver more consistent force on teeth while being comfortable to wear.
The polyurethane itself does not contain bisphenol rings in its chemical structure, which is an important distinction. That means BPA is not an intentional ingredient in the aligner plastic. However, the manufacturing process (thermoforming, where flat sheets are heated and molded over a model of your teeth) can alter the material’s chemistry in ways that matter.
BPA and Chemical Leaching
Several studies have found that aligners, including Invisalign, release trace amounts of BPA, a well-known endocrine disruptor with estrogen-mimicking activity. The amounts detected have consistently been below toxic thresholds, but the fact that any BPA appears is notable given that the base material is technically BPA-free.
Where does it come from? If you have composite resin attachments bonded to your teeth (the small tooth-colored bumps that help aligners grip), those are a likely source. One study measuring saliva during Invisalign treatment found that BPA concentrations were four times higher in patients who still had attachments compared to after attachment removal. The attachments are made from a different resin that can degrade and release BPA into saliva, especially when the aligner presses against them for 22 hours a day.
Beyond BPA, the aligner plastic itself can shed residual monomers (unreacted chemical building blocks) and degradation byproducts from its surface. Lab studies on human gum tissue cells showed a dose-dependent reduction in cell viability when exposed to extracts from several commercial aligners, including Invisalign, indicating slight to moderate toxicity at the cellular level. The thermoforming process significantly increases this effect, meaning the finished aligner is more chemically active than the raw plastic sheet it started as.
Saliva acidity plays a role too. More acidic conditions in the mouth can enhance the solubility of these chemical leachates, potentially increasing exposure for people who consume acidic foods or drinks or who have naturally lower salivary pH.
Microplastics From Daily Wear
This is the concern that has gained the most attention recently. Wearing aligners 22 hours a day means your upper and lower trays constantly contact each other during chewing, speaking, and swallowing. That friction causes visible surface damage: microcracks, grooves, abrasion marks, and distortions that appear within the first week of use.
That surface damage corresponds to the release of tiny plastic particles into your saliva. Researchers testing Invisalign and other aligner brands after simulated aging in artificial saliva found that all aligners released microplastics, predominantly in the 5 to 20 micrometer size range. Particles that small can be swallowed or potentially absorbed through oral tissues.
The surface degradation happens quickly and doesn’t appear to be strongly time-dependent. In other words, the damage occurs early in an aligner’s lifespan rather than steadily worsening. This is relevant because Invisalign users swap to a new tray every one to two weeks, meaning each fresh aligner goes through this initial degradation phase repeatedly over the course of treatment.
BPA Alternatives May Not Be Safer
Many aligner manufacturers market their products as “BPA-free,” and that’s technically accurate for the base plastic. But BPA-free doesn’t automatically mean free of similar compounds. Alternative bisphenol derivatives like BPS and BPF are commonly used in BPA-free plastics, and growing evidence suggests they carry similar endocrine-disrupting properties. Whether aligners release meaningful amounts of these alternatives hasn’t been thoroughly studied yet, but researchers have flagged it as a gap worth noting.
Allergic Reactions and Oral Irritation
Thermoplastic polyurethane is generally well tolerated, but it is more likely to cause allergic reactions than some other aligner plastics like PETG. The isocyanate component in Invisalign’s polyurethane formulation has been identified as a potential trigger for sensitive individuals. Symptoms can include oral mucosal irritation, redness, or discomfort that goes beyond normal adjustment soreness.
Studies on oral irritation from Invisalign aligners have found it to be minimal in most cases, with slight redness observed in some users. The mechanical friction of inserting, removing, and wearing the trays contributes to mucosal irritation independently of any chemical effect.
How Heat and Cleaning Affect Leaching
Higher temperatures accelerate plastic degradation, which is why you’re told never to drink hot beverages while wearing aligners. The combination of heat, mechanical stress, and salivary enzymes in the mouth creates conditions that promote chemical release from the plastic surface.
Cleaning methods matter too. Lab testing of aligner materials found that pure ethanol solutions extracted 11 different chemical compounds from the plastic. When the ethanol concentration dropped below 50%, no chemicals were detectable. This suggests that alcohol-based mouthwashes or cleaning solutions could potentially increase chemical leaching from your aligners, while water-based cleaning is much less likely to cause degradation.
Practical steps to minimize exposure: clean aligners with cool or lukewarm water, avoid alcohol-heavy cleaning products, never leave trays in a hot car or run them under hot water, and don’t eat or drink anything other than cool water while wearing them. These precautions won’t eliminate microplastic release from mechanical wear, but they reduce thermally and chemically driven leaching.
Putting the Risk in Context
Invisalign is FDA-cleared and has been used by millions of people since 1998 with no widespread reports of systemic toxicity. The chemical releases documented in studies are real but have been measured at levels below established safety thresholds. Cell-level toxicity in a lab dish doesn’t automatically translate to harm in a living person, where saliva dilution, swallowing, and the body’s metabolic processing all reduce effective exposure.
That said, the cumulative nature of the exposure is worth considering. Aligners sit against your oral tissues for 22 hours a day, treatment can last 12 to 18 months or longer, and each new tray introduces a fresh cycle of early surface degradation and microplastic shedding. The long-term biological effects of ingesting small quantities of polyurethane microplastics over that time frame are genuinely not well understood. This isn’t unique to Invisalign. It applies to all clear aligner brands using similar thermoplastic materials, and it mirrors broader scientific uncertainty about microplastic exposure from food packaging, water bottles, and other everyday plastic sources.