By Dr. Tracey Woodruff
Science is sounding the alarm. Microplastics have been found in breast milk, placental tissue, and even in newborns’ first bowel movements—meaning exposure begins before birth and continues for life. Inside the body, microplastics act like Trojan horses: they carry toxic additives like phthalates and Bisphenol A (BPA), absorb harmful pollutants like pesticides and heavy metals, and lodge in our organs.
As a professor and researcher at UCSF, I study how environmental contaminants affect pregnancy and child development. What we’re learning about microplastics is alarming. These tiny plastic particles, shed from packaging, clothing, tires, and consumer products, are impossible to avoid. We breathe them in, consume them in water, in food that has been contaminated with plastics, and even absorb them through skin contact.
Studies measuring microplastics in humans and their potential health effects have been rapidly increasing in number and findings. Researchers have measured 12 types of microplastics in human lung tissue. Another study estimates babies have ten times more microplastics in their feces than adults. Yet another found that microplastics in the intestines could increase the rate at which toxic chemicals are absorbed. Understanding and evaluating these findings rigorously is critical to informing the state of knowledge, and importantly, actions to prevent harmful exposures.
Accordingly, my team conducted the first systematic review using gold standard methods – meaning using rigorous, transparent, and consistent methods – to evaluate the health harms of microplastics for the California State Legislature. We evaluated almost 3,000 studies and we concluded they are “suspected” to harm reproductive health, which includes effects on sperm quality, digestive outcomes, which includes effects on the colon, and respiratory health, which includes effects on pulmonary function and lung inflammation. Importantly, microplastics can disrupt biological systems, like the immune system, and increase inflammation, which means they could also increase the risk of colon and respiratory cancers. Concerningly, colon cancers are increasing in young people, and nonsmoking lung cancers are also increasing.
We focused on the digestive, reproductive, and respiratory systems because the digestive system is the first point of contact for drinking and eating exposures, the reproductive system may be particularly sensitive to environmental insults, and the respiratory system has direct exposure to airborne microplastics.
We did not evaluate all the potential health outcomes from microplastics. Other studies have found links to other health outcomes. For example, a new study shows that microplastics can pass through the blood-brain barrier into the brain and that higher levels of microplastics were measured in people with dementia.
The study also found that the levels of microplastics in the organs measured (brain, liver, and kidneys) all showed significant increases in concentration between 2016 and 2024, which is consistent with the doubling of plastic production since 2008. Concerningly, microplastics have been found in other body parts, including lungs, spleen, liver, blood, and feces.
There are still gaps in knowledge about microplastics, including about their toxicity to humans, but we already know enough to be concerned. Microplastics are forever. Once in the environment, they only break down into smaller plastics, but don’t go away. The best solution to lower microplastic exposures is to reduce plastic and microplastic production. Yet plastic production is expected to triple in the next 30 years, which means more exposure and health harms. Chemicals that are in or on the microplastics can also have long half-lives, yet another reason to act swiftly to reduce microplastic production and its use in products.
California has an opportunity—and the responsibility—to act. Assembly Bill 823, currently on Governor Gavin Newsom’s desk, would take a meaningful step by banning intentionally added plastic microbeads in personal care and cleaning products. It addresses the deliberate use of microplastics in products we put on our bodies and use to clean our homes, workplaces, and schools. It’s not a complete solution—but it’s a critical move toward reducing exposures in our daily lives.
That brings us to plastic glitter, which would be banned in cosmetics under AB 823. Found in eyeshadows, lip glosses, nail polish, and body lotions, plastic glitter harms both people and the environment. Thankfully, safer, non-plastic alternatives already exist—so fear not, AB 823 won’t make the world any less sparkly.
Californians can’t solve this global crisis alone. But by taking action, we can spark the innovation, policy change, and accountability needed for a healthier future. California has led the way to better environmental health before, for example by banning toxic flame retardants in foam furniture (Assembly Bill 2998 in 2018), banning 24 toxic chemicals, including mercury and formaldehyde, from personal care and beauty products (Assembly Bill 2762 in 2020); removing toxic phthalates from IV bags and tubing (AB 2300 in 2024), amongst many examples.
Microplastics are not just an environmental issue—they’re a public health emergency. With AB 823, California has the chance to show once again that protecting our environment means protecting our people.
Dr. Tracey Woodruff is a professor and director of the Program on Reproductive Health and the Environment at the University of California, San Francisco.
