Microplastics have been detected in human blood, brain tissue, placentas, and tumors. Federal agencies have committed $144 million to study them. But if patients ask whether microplastics are giving them cancer, the most honest answer may be the least satisfying one: We don’t know, and we’re not close to determining a causal link.

While cancer is often included on the list of suspected dire consequences of microplastics exposure, that’s largely based on biological plausibility: Microplastics can trigger processes, such as chronic inflammation, oxidative stress, endocrine disruption, and DNA damage, that can precede cancer.

Evidence linking microplastic exposure to actual disease, however, just isn’t there.

“I know of no credible evidence that microplastics cause cancer,” said Philip Landrigan, MD, MSc, an epidemiologist and director of the Global Observatory on Planetary Health at Boston College in Chestnut Hill, Massachusetts.

At the same time, absence of causal evidence does not equate to “safe,” and research into microplastics and human health is in early days.

“I don’t think anyone should think that the presence of microplastics in human tissue is benign or harmless,” said Landrigan, who is co-chair of the Lancet Countdown on Health and Plastics, a global project aiming to track the health effects of plastics.

Regarding cancer, some of the fundamental questions are: Do microplastic particles precede tumors, or do tumors simply accumulate them? Is the risk from the particles themselves or the chemicals riding on them? And can scientists even measure individual exposure reliably enough to find out?

Why Microplastics Enter the Cancer Conversation

The interest is driven in large part by a cancer trend that needs an explanation: the rising incidence of early-onset colorectal cancer among people born after the 1960s.

It’s likely that environmental exposures are to blame, said Thejus Jayakrishnan, MD, a gastrointestinal medical oncologist at Dana-Farber Cancer Institute in Boston who works with the center’s young-onset colorectal cancer program.

However, the specific exposures are difficult to pin down. The suspected contributors include childhood obesity, physical inactivity, ultraprocessed foods, and changes in the gut microbiome. Microplastics also make the list as the same generations seeing rising colorectal cancer rates also grew up with dramatically more plastic in their food, water, and daily lives.

But disentangling microplastic exposure from other environmental factors is tough; ultraprocessed foods, for example, are a major source of microplastic exposure through industrial manufacturing and packaging.

A handful of small studies have found higher concentrations of microplastics in diseased tissue than in adjacent healthy tissue. They include a pilot study presented at this year’s American Society of Clinical Oncology Genitourinary Cancers Symposium involving 10 patients who’d undergone surgery for prostate cancer. Researchers found roughly 2.5 times more microplastics in the patients’ tumor tissue than in normal tissue.

The study garnered media attention at the time. But lead investigator, Stacy Loeb, MD, MSc, stressed that no conclusions can be drawn about causality.

“It is also possible that tumor tissue allows microplastics to accumulate more than benign tissue,” Loeb, a professor of urology and population health at NYU Grossman School of Medicine in New York City, told Medscape Medical News.

She said she was motivated to study microplastics in prostate tissue after reading a 2024 New England Journal of Medicine study of patients who underwent surgery for asymptomatic carotid artery disease. It found that patients whose plaques contained microplastics were 4.5 times more likely to have a heart attack or stroke over the next 3 years vs those who had no microplastics detected.

A separate study from the same group, published in the European Heart Journal, found higher microplastic concentrations in the coronary and peripheral blood of heart attack patients compared with patients who had clear arteries on cardiac catheterization. Smoking emerged as the only independent predictor of microplastic detection — which could mean that smoking wreaks havoc, in part, by depositing microplastics in the arteries or that smoking was a confounder.

Similar tissue-detection work has been reported in colorectal and brain tumors, but all the studies are small, cross-sectional, and none demonstrate that microplastic accumulation preceded the disease.

What Existing Evidence Shows

The most damning evidence against plastics involves their chemical cargo, not the particles themselves. The International Agency for Research on Cancer (IARC) has classified several plastic monomers and additives as carcinogens, including vinyl chloride (Group 1) and styrene (Group 2A). Endocrine-disrupting chemicals like bisphenols and phthalates, which leach from plastic products, have consistent evidence for hormone-driven cancers in adults.

“PFAS chemicals are strongly linked to testicular cancer, according to IARC, and phthalates are classified as a possible carcinogen,” Landrigan said. “Vinyl chloride, used in PVC [polyvinyl chloride] production, is a known cause of liver cancer.”

But for the physical microplastic particles that currently dominate public concern, the evidence is far thinner. Laboratory and animal studies show they can induce processes like inflammation, oxidative stress, and microbiome disruption — all plausible precursors to cancer.

However, no human epidemiologic study has linked microplastic exposure to cancer incidence, and the field faces basic challenges such as a lack of standardized methods to even measure individual exposure.

In July, the Environmental Protection Agency excluded microplastics from its latest drinking-water monitoring rule, citing the absence of a validated analytical method, even after committing to a $144 million research program on plastics and health earlier in the year.

“Before people feel comfortable talking about a cause-and-effect relationship, they want to see several different studies done by different teams in different populations that show convergent results,” Landrigan said. “We’re not there yet.”

What to Tell Patients

Clinicians fielding patient questions about microplastics can acknowledge the uncertainty without dismissing the concern.

“If anything, the data points more towards harm than not,” Jayakrishnan said. “But the definitive data, and how to mitigate that, is lacking.”

He recommended that patients primarily focus on cancer risk factors with strong evidence behind them — smoking, alcohol, obesity, and physical inactivity. But they can also be mindful of unnecessary plastic exposure where practical. That could mean avoiding single-use plastics, not heating food in plastic containers, and using glass or steel for food storage, for example.

Jayakrishnan also cautioned that patients should steer clear of supplements now being marketed to absorb and remove microplastics from the body. No clinical trial has shown that those products lower microplastic levels in human tissue.

In contrast to supplements, there is a procedure, therapeutic plasma exchange, that has been shown to remove some microplastic particles from the bloodstream. The most important question, however, remains unanswered: Does it do any good?

Landrigan reported receiving support and consulting fees from the Minderoo Foundation and the Centre Scientifique de Monaco. Loeb reported receiving funding from or serving as an advisor to Endo USA, Blue Earth Diagnostics, and other companies. Jayakrishnan reported receiving honoraria or research support from Primum Health and Takeda Oncology.