According to a survey from Statista, about a quarter of U.S. children wear school uniforms. About one-fifth of U.S. public schools require uniforms, with the greatest prevalence in elementary and low-income schools. They are even more common in Catholic and other private schools in the United States and Canada. A new study by researchers at Indiana University, the University of Toronto, the University of Notre Dame and the Green Science Policy Institute shows that children who wear stain-resistant school uniforms may be exposed to potentially harmful levels of chemicals. The study, published in Environmental Science & Technology, found that millions of schoolchildren in the U.S. and Canada are exposed to potentially harmful levels of per- and polyfluoroalkyl substances through their uniforms. The researchers detected the chemicals in all of the stain-resistant school uniforms they tested from nine popular brands. Most products had concentrations as high as those in outdoor clothing. Marta Venier, an assistant professor in IU's O'Neill School of Public and Environmental Affairs, says per- and polyfluoroalkyl substances don't belong in any clothing, but their use in school uniforms is particularly concerning because they are worn directly on the skin for up to eight hours per day by children, who are particularly vulnerable to harm. Some of these chemicals have been associated with a wide variety of serious health issues, such as cancer, obesity and more severe COVID-19 outcomes. They've also been found to contaminate the drinking water for millions of citizens. Only a small fraction of the thousands of them have been tested for toxicity, and all are either extremely persistent in the environment or break down into extremely persistent per- and polyfluoroalkyl substances. Additionally, some newer ones first claimed to be safe have later been determined to be harmful to human health. These chemicals in treated uniforms may end up harming children through skin absorption, as well as from eating with unwashed hands, other hand-to-mouth behaviors and mouthing of clothing by younger children. The primary type found in the uniforms also pose an inhalation risk. Further, these uniforms are a source of per- and polyfluoroalkyl substance contamination in the environment when they are worn, laundered and discarded or recycled. The findings come as legislation to phase out these chemicals in textiles, which would include school uniforms, moves forward in New York and California. California's Assembly Bill 1817, known as the Safer Clothes and Textiles Act, was signed by the governor on September 29 while New York's Senate Bill S6291A is still awaiting the final governor’s signature. The researchers recommend that parents check labels to see if their children's uniforms are marketed as stain resistant. If so, they say there is some evidence to suggest that multiple washes can reduce the chemical concentration. They also say that used clothes or hand-me-down clothes are better options, because the levels of these chemical substances might decline with laundering.