More Microplastics in Glass Than Plastic? Here’s What the Research Says

For years, many health-conscious consumers have reached for glass bottles over plastic, assuming they’re the safer, cleaner alternative. But a new study out of France challenges that belief, showing that glass bottles may actually contain more microplastics than plastic ones with one unexpected culprit the cap.

Where the Microplastics Are Coming From

Microplastics are defined as plastic fragments smaller than 5 micrometers, and they’ve been found in everything from drinking water to table salt and even inside the human body. While switching to glass seems like a reasonable way to reduce exposure, French researchers recently found that beverages in glass bottles actually showed higher microplastic levels compared to those in plastic containers or aluminum cans.

The surprising source? The bottle caps. Many glass containers use plastic-lined or painted caps, and these were often scratched or damaged likely shedding microplastic particles directly into the drink.

Researchers observed that many of the microplastics found in glass-bottled water and soda were the same color as the caps, linking them directly to packaging materials. Interestingly, wine bottles sealed with corks showed much lower levels of contamination, pointing to the cap as a critical risk factor.

“I do think there’s a false sense of security when we use glass,” said Mary M. Johnson, MD, PhD, a research scientist at Harvard, who was not involved in the study.

How Microplastics Are Measured And Missed

The study used a type of spectroscopy (FTIR) to detect particles, but this method doesn’t pick up the smallest microplastics specifically nanoplastics, which are less than 1 micrometer in size. That means the actual amount of plastic in glass bottles could be even higher than reported.

Compare that to a recent study that used a more sensitive method to examine bottled water and found that a single liter contained up to 240,000 plastic particles, 90% of which were nanoplastics.

Microplastics Are Everywhere

Even if you’re diligent about your packaging choices, microplastics are nearly impossible to avoid completely. They’ve been found in:

• Rice, salt, and processed foods

• Canned fish

• Tea brewed in plastic-based tea bags

• Food microwaved in plastic containers

• The air we breathe

And now, even glass bottles are under scrutiny.

While the long-term health impacts of microplastic exposure are still being studied, emerging research links them to serious concerns including cardiovascular disease, reproductive issues, and even cognitive decline.

“Studies have been coming out showing microplastic exposure is linked to things like dementia, cardiovascular disease, mortality, and fertility,” said Johnson. “We just don’t yet know what the threshold is.”

What You Can Do to Reduce Exposure

Although we can't fully eliminate microplastics from our lives, a few mindful choices can help reduce your intake:

• Choose glass containers with cork or metal lids, rather than plastic or painted caps

• Avoid microwaving or freezing food in plastic containers

• Brew tea using loose leaves or plastic-free bags

• Filter tap water using systems certified to reduce microplastic content

• Limit consumption of heavily processed and packaged foods

The Bottom Line

Glass containers aren’t automatically safer than plastic when it comes to microplastics—especially if the cap is made of plastic or has a painted interior. As science continues to uncover the pervasiveness and potential health impacts of microplastics, taking small steps to limit exposure wherever possible remains a wise move.

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