It wasn’t that long ago when microplastics were fringe-y science. You’d hear social media rumblings and see headlines saying we ingest a credit card’s worth of plastic every week.

But slowly, especially over the past few years, the magnitude of the problem emerged. Microplastics are everywhere — in the air we breathe, the water we drink, the food we eat.

And they’re in us: Our organs, our arteries, our lungs, our brains.

What we don’t yet have: More data-supported conclusions about what microplastics do to our health. Experts suspect and surmise many things, common sense suggests plenty, but the research has to catch up.

For example: Plastics contain approximately 16,000 different chemicals, explained Sarju Ganatra, MD, director of the Cardio-Oncology Program at Lahey Hospital and Medical Center in Burlington, Massachusetts. Of those, researchers have yet to study 10,000. Among the 6000 chemicals we do understand, 70%-90% are considered harmful to very harmful.

“We would not ingest them in isolation, we would not put that in our food,” he said.

And yet we do ingest them — while no definitive research exists on just how much plastic we take in. “There are studies that state that the weekly intake is up to 5 g of plastic, which corresponds to the weight of a credit card. Other studies show way lower values. So this is really still an ongoing development,” said Christian Pacher-Deutsch, a researcher studying microplastics in the human gut at CBmed GmbH, Graz, Austria, as well as the Medical University of Graz.

(If the persistent credit card comparisons aren’t colorful enough, a recent study estimated we carry about a spoonful of plastic in our brains.)

More human and animal studies are happening, and real data has begun to accumulate. This story will review some of the latest.

The problem: Plastic is accumulating faster than we can research its harm. Plastic production and use reached 435 million tons in 2020, according to a 2024 report from the Organization for Economic Co-operation and Development, and will increase by 70% by 2040 if nothing changes. Plastic leakage into the environment will also increase to 30 million tons in the same timeframe, a 50% jump from 2020 levels.

The Body’s Battle Against Little Plastic Invaders

Microplastics are particles < 5 mm in diameter — about the size of a sesame seed or smaller. Nanoplastics, considered a subset of microplastics, are < 1 µm. These tiny plastics form when larger plastics break down through heat, abrasion, weathering, and sunlight exposure. These particles can be as small as nm, allowing them to penetrate cell membranes and cross biological barriers.

Some of the microplastics we breathe originate from the ocean. “Ocean water evaporates every single day, even in the coldest month of the winter. It’s never static,” Ganatra explained, and with that evaporation tiny plastic particles float into the air, too.

He led teams studying the impacts of airborne microplastics on neurologic conditions and cardiometabolic health. The two studies, published earlier this year, indicate that living in coastal cities with higher levels of airborne microplastics correlates with slightly increased risk for cognitive disability and cardiometabolic diseases.

“Plastic does not belong in the brain or the heart,” Ganatra said.

Agencies including National Oceanographic agencies and NASA have measured microplastic concentrations in air across various regions. The Atlantic coast and Gulf of Mexico cities tend to have higher amounts than Pacific cities. While other factors — like air pollution or obesity rates — could influence risk, both studies adjusted for general air pollution, cardiovascular and neurologic risk factors, plus ethnicity, gender, age, education, socioeconomic status, language, and other factors, Ganatra noted.

Drinking Water, Plastics, and Brain Health

Jaime Ross, PhD, neuroscience professor at The University of Rhode Island, Kingston, Rhode Island, studied microplastic and nanoplastic exposure via drinking water in otherwise healthy young and old mice for just 3 weeks and observed changes in cognition and behavior. That 2023 study showed that those mice also developed decreased GFAP levels — a signature linked to early Alzheimer’s disease — in their microglia. This prompted further research on microplastics’ impact on Alzheimer’s-like genetically engineered mice.

“We chose polystyrene because it is one of the most abundant polymers in the environment and one of the most readily used. It’s also in styrofoam cups, plastic cups, takeout containers, so we are certainly in contact with that,” Ross said. They selected spherical polystyrene particles measuring 0.1 and 2 µm — without jagged edges that could cause cell damage — at concentrations well below toxic levels.

After 3 weeks of consuming water with microplastics, behavioral tests revealed striking differences. “If you’ve ever had a mouse in your house, you know it goes along the walls, right? It’s not going to sit in the middle of the room,” Ross noted. But Alzheimer’s-like male mice that consumed microplastics spent more time in the center of the testing arena. Females didn’t exhibit this behavior but performed worse on discrimination index challenges, measuring their ability to identify previously seen objects.

These results, Ross explained, “actually match reasonably well, or quite well, with what human Alzheimer’s patients experience. So human female Alzheimer’s patients experience a higher degree of change in memory, whereas male Alzheimer’s patients typically experience bigger changes in apathy.”

Related to Ross’s findings, another study this year indicated that the brains of people who had dementia contained more microplastics and nanoplastics than those without dementia.

Plastic’s Hidden Impact on Gut Health

Studies in mice have also found that microplastics can affect their gut microbiome— the trillions of bacteria, viruses, and fungi living in the digestive system that influence everything from digestion to immune function and mental health.

Since microplastics appear in human feces, Pacher-Deutsch led a study of their potential impacts on the human microbiome. As deliberately feeding people microplastics would be unethical, they used a bioreactor inoculated with fresh human stool samples from five healthy people. Inside the bioreactor, they kept microbes alive while monitoring population responses to various microplastics — polystyrene, polypropylene, low-density polyethylene, poly (methyl methacrylate), and polyethylene terephthalate — using both realistic human exposure levels and higher concentrations to assess dose-dependent effects.

They found that microplastic exposure consistently lowered pH levels in treated cultures vs control individuals, signaling shifts in microbial metabolism. Bacterial composition changed in response to specific microplastic types, with distinct increases and decreases in certain bacterial populations — including Lachnospiraceae, Oscillospiraceae, Enterobacteriaceae, and *Ruminococcaceae *— predominantly within Bacillota, a phylum central to digestion and gut health. Notably, several microplastic-driven microbial patterns mirrored those associated with conditions like depression and colorectal cancer.

These compositional changes coincided with altered bacterial metabolite production, partially explaining the pH drops. Different microplastics triggered unique metabolic responses, which, Pacher-Deutsch said, “tells us that specific pathways within the microbiome might be disrupted or might be influenced by the plastics, for example, the short-chain fatty acid metabolism might be affected by the presence of microplastics.”

“A lot of impacts of microplastics on the whole gastrointestinal tract have been proposed by different publications, including changes in mucosal viscosity, changes in the bioavailability of micronutrients, also changes in the bacterial compositions,” Pacher-Deutsch noted. He added, “more research is necessary to really pinpoint the effects.”

Utility vs Futility: Taking Action Against Microplastics

Ganatra believes the scientific community is underestimating plastic’s impact on our health. Microplastics in our bodies, he said, “cause inflammatory reactions. They don’t belong to the body, and it activates the immune system, which causes a chronic, low-degree inflammation. That’s the basis for many diseases we deal with today, including cancer, cardiovascular disease and neurological diseases.”

“People think that plastic is inert and it’s stable. Instead, we are realizing it sheds,” Ross said. She recommends examining all your plastic exposures in a given day — your coffee maker, plastic-lined disposable cups, cooking utensils, straws — then consider switching to glass or stainless steel. Heat plus plastic especially accelerates microplastic shedding, she noted. She also warned that many clothes shed plastics, so choosing materials like cotton, wool, and silk, while more expensive, may benefit health.

“We probably underestimate the power we have as individual consumers because at the end of the day, the market is much larger than any one of us, but we have to remember that it is shaped by us,” Ganatra said.

Ganatra also runs a nonprofit called Sustain Health Solutions, which aims to reduce plastic in the healthcare system — where tremendous amounts of single-use plastic are discarded daily. But change isn’t easy, he noted: “A steel instrument, and having an autoclave, and having energy to run that, and having personnel to do that, and all these things need huge capital investment.”

Researchers have a role too, Pacher-Deutsch said, “we need to go deeper in the health implications and find out as much as possible about the variety of plastic types that’s out there so that we can actually make research-based decisions and give recommendations to health authorities.”

“I think we need to think a little bit beyond tomorrow. We need to think more as a ‘one health’ concept, where planetary health is not separate from our health or from other animals’ health,” said Ganatra.