How Do Microplastics Harm the Body? Scientists May Have Discovered One Possibility

Plastics Common in Food Containers and Bottle Caps Did the Most Damage

All six plastics produced free radicals when exposed to water, but some produced far more than others. The most water-repelling plastics, polyethylene and polypropylene, were the most reactive, and PET and acrylic were the least reactive.

When the researchers tested what the hydroxyl radicals could do, a common protein clumped together at the plastic surfaces — a sign that its structure had been damaged.

Adding a substance that neutralizes free radicals reduced clumping, suggesting that the radicals caused the damage.

In later experiments, red blood cells from mice broke into fragments after direct contact with the plastic particles. “The plastics that were most reactive at the surface did the most damage. That included polypropylene and polyethylene, the plastics used in a lot of food containers, packaging, and bottle caps,” says Patel.

Water Molecules Behave Differently at the Surface of Plastic

“The surprising part is that neither the plastic nor the water needs to be chemically unusual. What matters is the boundary where they meet,” says Min.

Water molecules behave differently when they’re in contact with the surface of plastic, and that shift creates conditions where reactive molecules can form, he says. “You can think of this as a special chemical environment that emerges when two otherwise familiar materials come into contact,” says Min.

Over time, plastic breaks into smaller pieces. That process can accelerate with exposure to heat, sunlight, and wear and tear, such as squeezing a bottle or opening and closing its cap.

The smaller the pieces get, the more surface area they have relative to their mass, which means more of the plastic is in contact with water and may make these reactions more important, says Min.

Findings Suggest Not All Plastics Are Equal

Researchers already know microplastics are everywhere, says Patel. “What we’re still figuring out is how they might cause harm. This study offers one explanation: The particle’s surface may generate damaging molecules directly,” she says.

“It also suggests that not all plastics are equal. The more reactive types caused more damage. That could eventually help us prioritize which plastics to phase out of food contact and products used by children,” she says.

Strengths and Limitations of the Study

The findings of the study were consistent: The lab experiments and computer simulations pointed to the same explanation, and the effect showed up in all six common plastics tested.

But it’s also important to be clear about what the study is and isn’t, says Patel. “These are lab experiments. They don’t show this is happening in people’s bodies, or at what doses,” says Patel.

“It is also important to emphasize that science has not yet established exactly what levels of microplastic exposure cause harm in humans,” says Min.

Next, researchers want to learn whether these reactions cause damage in living cells and tissues, and if the effects depend on the type of plastic and the size of the particles, he says.

Simple Ways to Reduce Microplastic Exposure

Microplastics are so widespread that avoiding them completely probably isn’t realistic, says Min. “I would encourage people to take reasonable precautions without becoming unnecessarily alarmed,” he says.

“This study doesn’t change what I do so much as reinforce it. If anything, it suggests that even ‘clean’ plastic without BPA or other additives may not be harmless, so ‘BPA-free’ shouldn’t be the end of the conversation,” she says. BPA, or bisphenol A, is a chemical used in some plastics that has been linked to fertility issues.

When asked what they do in their own lives, both experts described a few simple steps they take to reduce their exposure to microplastics.

Don’t Reheat Food in Plastic

“I try to take simple, practical steps to reduce unnecessary plastic exposure, particularly where plastics come into direct contact with food and drinking water,” says Min. He generally prefers reusable glass or stainless steel containers when it’s convenient and avoids heating food in plastic containers, he says.

Patel, “as a pediatrician and a mom,” says she follows a similar strategy. “I don’t microwave food in plastic. Heat increases how much plastic sheds, and studies have found polypropylene baby bottles release large numbers of particles when heated,” she says. She also keeps plastic out of the dishwasher.

Children are likely to bear more of whatever risks microplastics pose, she says, because relative to their size, they eat, drink, and breathe more than adults, and their bodies are still developing.

Avoid Bottled Water When You Can

Bottled water is another source of exposure that most experts recommend avoiding or limiting. A study published in 2024 found an average of 240,000 tiny plastic particles per liter of bottled water.

Glass and stainless steel water bottles are the best choices for avoiding microplastics. If you do use plastic bottles, don’t reuse single-use ones, and avoid leaving them in a hot car or direct sunlight.

Still, individual choices only go so far; the real solution is to produce less plastic and set stronger safety standards, says Patel.

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