They’re in the water we drink, the food we eat, the clothes we wear, and the air we breathe. They’ve pervaded every ecosystem in the world, from coral reefs to Antarctic ice. And they’ve infiltrated the human body, lodging themselves in everything from brain tissue to reproductive organs.

Microplastics – plastic fragments up to 5 millimeters long – are inescapable. An estimated 10 to 40 million metric tons of these particles are released into the environment every year, and if current trends continue, that number could double by 2040. Most come from larger plastic items that break down over time, while some are added directly to products we use such as paint, cleansers, and toothpastes.

“Plastic never goes away – it just breaks down into finer and finer particles,” said Desiree LaBeaud, MD, a pediatric infectious diseases physician at Stanford Medicine who co-founded the university’s interdisciplinary Plastics and Health Working Group.

Public concerns over the health effects of microplastics are growing. In the past year alone, headlines have sounded the alarm about particles in tea bags, seafood, meat, and bottled water. Scientists have estimated that adults ingest the equivalent of one credit card per week in microplastics. Studies in animals and human cells suggest microplastics exposure could be linked to cancer, heart attacks, reproductive problems, and a host of other harms. Yet few studies have directly examined the impact of microplastics on human health, leaving us in the dark about how dangerous they really are.

While avoiding microplastics is impossible, experts at Stanford Medicine point out that individuals can take steps to reduce their exposure. Addressing the problem on a broader scale will require action from industry leaders and policymakers, they say.

The promise and peril of plastics

The age of plastics dawned in 1907, when Leo Baekeland, a Belgian chemist who’d emigrated to the United States, invented the first fully synthetic plastic while searching for a shellac substitute. Manufacturers soon realized the new material was both inexpensive and highly versatile – it was durable, flexible, light, non-flammable, and didn’t conduct electricity. They began using it to produce everything from radios to cars to appliances. In the 1930s and 1940s, scientists invented new forms of the material, including polyester, nylon, Styrofoam, and Plexiglas.

Plastic production exploded in the 1950s. A Life magazine story from 1955 titled “Throwaway Living” lauded the spread of disposable items, such as single-use plastics, as a godsend for housewives drowning in chores. It was also a boon for industry, becoming critical to modern medicine, construction, apparel, food packaging, and more.

By the late 1960s, experts began warning about the dangers of plastic pollution, including islands of debris clogging the oceans. In the 1970s, researchers observed small pieces of plastic in marine plankton. The term “microplastics” was first used in 2004 (particles less than 1 micrometer in size are known as “nanoplastics”). Researchers discovered that plastic fragments were being spread by wind and water, contaminating everything from the depths of the oceans to the summit of Mount Everest.

Plastic contaminates ecosystems worldwide, with debris found from the ocean floor to Mount Everest’s summit, threatening the planet’s wildlife. | Richard Carey / Adobe Stock

The durability of plastic molecules contributes to their staying power – scientists believe that all the plastic ever made, besides that which has been incinerated, is still around in a form that can’t degrade naturally (burning plastic releases toxic chemicals and heavy metals). To date, microplastics have been found in 1,300 species, including throughout the human body.

How harmful are microplastics?

Research on the health impacts of microplastics in humans is just beginning. The particles have been found in multiple organs and tissues, including the brain, testicles, heart, stomach, lymph nodes, and placenta. They’ve also been detected in urine, breastmilk, seme, and meconium, which is a newborn’s first stool. “We’re born pre-polluted,” LaBeaud said.

Evidence is growing that this exposure could be harmful. Studies show that microplastics make fish and birds more vulnerable to infections. Animal and cellular studies have linked microplastics to biological changes including inflammation, an impaired immune system, deteriorated tissues, altered metabolic function, abnormal organ development, cell damage, and more. A recent large-scale review of existing research by scholars at the University of California, San Francisco, concluded that exposure to microplastics is suspected to harm reproductive, digestive, and respiratory health and suggested a link to colon and lung cancer.

One of the first papers to directly examine the risks of microplastics exposure in humans, published in The New England Journal of Medicine in March 2024, studied patients undergoing surgery to remove plaque from their arteries. More than two years after the procedure, those who had microplastics in their plaque had a higher risk of heart attack, stroke, and death than those who didn’t.

Inspired by this research, Juyong Brian Kim, MD, an assistant professor at Stanford Medicine, is conducting pilot studies to investigate the effects of microplastics and nanoplastics on animals and on human cells that line blood vessels. So far, his research shows that these plastics can get inside cells and lead to major changes in gene expression. “These findings suggest that the particles contribute to vascular disease progression, emphasizing the urgency of studying their impact,” he said.

“Although data is still quite limited, maybe all these epidemics that we have – obesity, cardiovascular disease, everybody getting cancer – are related,” LaBeaud said. “People are trying to figure out if they’re associated with the plastics that we’re inhaling and imbibing.”

Children, whose organs are still developing, could be at higher risk of harm. Kara Meister, MD, a pediatric otolaryngologist and head and neck surgeon at Stanford Medicine, noticed that thyroid cancer was becoming more common among her patients and was often linked to autoimmune disease. Considering what could be disrupting kids’ hormones, she decided to research microplastics.

In early 2024, Meister and her team began looking for microplastics in tonsils they’d removed from healthy children with conditions such as sleep apnea. “What we found is there are definitely microplastics in a high proportion of pediatric tonsil tissue, and they seem to be not only on the surface but also deep within,” she said. In one child’s tonsils, the team found specs of Teflon visible with a microscope.

Next, Meister and her team are developing techniques to identify and quantify the microplastics they’re finding and to determine where exactly they’re embedded. Eventually, her aim is to illuminate the potential role of microplastics in pediatric thyroid disease. “We have a long way to go,” she said.

Avoiding nonstick and plastic cookware, wearing clothes made of natural fibers, and seeking out plastic-free toiletries and cosmetics can likely lower health risks related to microplastics. | wachiwit / Adobe Stock

Scientists don’t yet know how long microplastics stay in the body or how effects are tempered by genetics, the environment, or other factors. They haven’t determined whether some plastics or forms of exposure are worse than others. Nor do studies exist on the direct dangers of microplastics in humans. “Because plastic is so ubiquitous, it’s difficult to have a lot of evidence that’s causal,” LaBeaud said. “It’s not like we’re going to have randomized control trials where people aren’t exposed.”

Research is also complicated by the fact that scientists lack standardized techniques for identifying and quantifying microplastics. (With funding from the Sustainability Accelerator at Stanford’s Doerr School of Sustainability, Meister is part of a team developing user-friendly, portable devices they hope will democratize measurement of microplastics.) Nanoplastics are even harder to track yet may do the most damage. “It’s certainly not proven, but if something is small enough to get intracellular, it may have more implication to cellular function or signaling,” Meister said.

Most existing studies fail to account for the multiple sizes, types, and shapes of real-world plastic particles. Researchers also struggle to know which substances to study, as more than 10,000 chemicals are used to make plastic; two-thirds have not been assessed for safety, while over 2,400 are considered potentially toxic. Eliminating contamination is also difficult, as many laboratory materials are made of plastic.

Still, research is growing exponentially, and Meister believes more studies about the effects of real-world microplastics in humans are around the corner. “Probably within the next year or two, we’ll have a couple more big landmark papers,” she said.

What can be done?

In the meantime, consumers can measure their own microplastics levels through commercially available tests. Million Marker, founded by Jenna Hua, an environmental health scientist and dietitian who completed a postdoctoral fellowship at Stanford Medicine, offers a mail-in kit that screens urine. Meanwhile, Blueprint Bryan Johnson, founded by the eponymous entrepreneur and venture capitalist, makes one that measures levels in the blood. However, Meister cautions that it’s unclear how the amount of microplastics in urine relates to that in the body, and that the Blueprint tests lack transparency about its methods.

While microplastics are unavoidable, LaBeaud and Meister agree that reducing exposure likely lowers health risks. “All of us need to stop using plastic as much as we can to protect our health, especially single-use plastics,” LaBeaud said.

She suggests avoiding nonstick and plastic cookware, wearing clothes made of natural fibers, and seeking out plastic-free toiletries and cosmetics. She opts for peanut butter and beverages in glass jars and cooks at home as much as possible; when ordering out, she asks restaurants to put food in a glass container she brings along. She recommends foil instead of plastic wrap and metal or wooden toys for babies and small children.

Heat likely increases leaching, so Meister encourages hand-washing plastic items and not using plastic containers to reheat food in the microwave. Wear and tear may also increase exposure to particles, so she suggests not reusing degraded plastic items.

Living a healthy lifestyle, including adequate sleep, a balanced diet, and reducing stress, may also help. “Just because you have a little plastic in you doesn’t necessarily mean doomsday,” Meister said. “Giving your body the best shot to deal with whatever might come along is the best you can do.”

Ultimately, decreasing microplastics in the environment will require action from corporations and regulators. The U.S. and Europe have banned cosmetics containing plastic microbeads, and in 2018, California became the first state to require testing for microplastics in drinking water (monitoring has yet to begin). In 2023, the European Union adopted restrictions on microplastics intentionally added to products, and the U.S. federal government has set a goal of eliminating single-use plastics from all operations by 2035.

LaBeaud argues that’s not enough when at least 450 million metric tons of plastic are produced every year, an amount expected to triple by 2060. She says policymakers should set caps on plastics production, eliminate all unnecessary single-use plastics, phase out all toxic substances used in plastics manufacturing, and pass a global treaty to end plastics pollution.

LaBeaud is experimenting with innovative ways to reduce plastic waste. The Health and Environmental Research Institute, a nonprofit she formed in Kenya, is seeking funding to feed plastic to black soldier flies, which become feed for chickens that in turn produce excrement that serves as fertilizer. LaBeaud is planning a research project to ensure the process does not spread microplastics. 

Consumers and professional organizations, including those in the medical field, should also demand action from companies to develop healthier alternatives to plastic, LaBeaud says. “Individuals need to recognize that we have a lot of agency, and we can make choices that actually do change things,” she said.