“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.

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.”

- Microplastics and our health: What the science says

Microplastics’ physical properties are one source of potential hazards. Some marine organisms seem to be eating more microplastics and fewer nutrients, which can reverberate up the food chain. In humans, researchers point to illnesses caused by particulate air pollution, which contains microplastics, and by workplace exposure to plastic dust.

Other threats arise from chemicals in and on microplastic particles, including plastic components — such as BPA, phthalates, and heavy metals — that are known or suspected to cause disruption to nervous, reproductive, and other systems.

Although the variety of microplastics and the difficulty of estimating accumulation in human tissues make it challenging to pin down risks, findings in models show inflammation, cell death, lung and liver effects, changes in the gut microbiome, and altered lipid and hormone metabolism.

Mounting evidence suggests that microplastics magnify the potency of other toxicant exposures, such as cadmium, as Demir and Turna Demir have confirmed in fruit flies and Lemos has confirmed in mice and fruit flies. Others are chasing down hints that microplastics can carry antibiotic-resistant bacteria and other pathogens on their surfaces and into our bodies.

- Microplastics Everywhere | Harvard Health Magazine