A study published in November investigated the release of micro and nanoplastics from three empty tea bags purchased from Amazon, online shopping site AliExpress, and from a supermarket. They found that tea bags made with the plastic substance polypropylene—used to heat-seal tea bags shut—released about 1.2 billion small pieces of plastic per milliliter of tea, while bags made with nylon-6 released 135 million pieces, and those made with cellulose released 8.2 million nano-range (extremely tiny) plastic particles.

Microplastics have been a growing concern, as scientists have discovered their increasing presence in soil, as well as fruits and vegetables, and meat and seafood. While it’s difficult to understand how much microplastics impact our health, scientists have researched their effect on animals. Studies on mice showed exposure to microplastics can disrupt the gut biome, lower sperm quality and testosterone, and impair learning and memory.

Experts have also told Fortune that it’s important to avoid exposure to chemicals often found in plastic—like endocrine disruptors, which interfere with our body’s hormone function. But more research is proving just how difficult that is, with the growing presence of micro- and nanoplastics in everything from our food and our clothes to our tea bags.

Here’s what we know about microplastics and how they may potentially damage our health.

Do microplastics pose a threat to health? 

Researchers in the tea bag study recognized that determining the harm posed by microplastics exposure is a “challenge.” But more evidence is emerging about the threat they present—especially as humans are almost constantly exposed to them.

A study published in March 2024 found that patients with microplastics or nanoplastics discovered in their neck arteries (while undergoing a procedure to remove plaque from the carotid arteries) had a higher risk of heart attack, stroke, or any cause of death than those who didn’t have micro- or nanoplastics in their arteries.

The authors of that study pointed out that microplastics can increase inflammation. Moreover, the study population that had microplastics in their bodies had more instances of hypertension and higher cholesterol—but more of them were also smokers, which could impact the results as well.

Many plastics are also made with endocrine-disrupting chemicals, which can disrupt function of the following:

• Glucose metabolism
• Thyroid function
• Fat metabolism
• Bone metabolism
• Reproductive hormones, which can lead to infertility and certain cancers including breast, kidney, and prostate, according to the EPA.

Which tea bags are safest?

The three types of tea bags that the researchers tested are commonly found in your grocery store or online. But which tea bags should you avoid at the grocery store?

According to the Center for Environmental Health, at least the following brands of tea contain microplastics:

• Tazo
• Teavana (Starbucks)
• Celestial Seasonings
• Mighty Leaf Teas

These brands, according to the Center, don’t use plastic in their tea bags:

• Traditional Medicinals 
• Pukka
• Numi Teas
• Republic of Tea
• Stash
• Yogi Tea

If you’re concerned about all tea bags, you can always opt for loose leaf tea, which you can steep using a metal or food-grade silicone tea infuser.

The most common sources of microplastic exposure

While tea bags present their own concerns about microplastic exposure, they are far from the only place from which tiny plastic particles are entering your body.

One of the biggest sources of micro- and nanoplastics consumption is our food supply. A study from December 2023 published in the journal Environmental Pollution looked at the amount of microplastics in 16 commonly consumed proteins (meat, seafood, and plant-based). 

It found that unprocessed or minimally processed proteins had the lowest levels of microplastics, while more heavily processed proteins like breaded shrimp and chicken nuggets had some of the highest concentrations. From meat alone, however, researchers determined people are ingesting as much as 3.8 million microplastics per year.

Other studies have found micro- and nanoplastics in fruit and vegetables such as carrot, lettuce, broccoli, potatoes, apples, and pears—likely from the concentrations of plastics found in soil, which a study from 2021 found. That plastic, researchers wrote, gets into the soil from plastic packaging, clothing—especially made from acrylic and polyester—and the wastewater from washing clothes, microbeads in personal care products, and other plastic debris.

Even salt can be a site of microplastic exposure. A 2022 study found that coarse himalayan pink salt had the highest concentrations of microplastics, followed by black salt and rock salt.

And one of the biggest staples in diets worldwide can be riddled with microplastics: rice. Researchers at the University of Queensland, Australia published their findings in 2021, which revealed that people are consuming three to four milligrams of plastic for every 100 grams of rice they eat—with the number jumping to 13 milligrams per serving of instant rice, which has four times more plastic in it than traditional rice. They did find, however, that washing rice before cooking it can reduce plastic contamination by 20% to 40%.

The key to reducing your exposure, experts have said, is to limit your plastic consumption overall. We know that bottled water can leach thousands of plastics into your body, with a one-liter plastic bottle containing some 240,000 plastic fragments on average.

Experts previously told Fortune that refraining from microwaving, cooking, or even storing and freezing food in plastic is a simple step that you can take to reduce your exposure to microplastics and the chemicals within them. They also said to try to eat lower on the food chain to avoid higher concentrations of plastics and endocrine disruptors in the bodies of animals that consume plants and other prey that contain microplastics.

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