Levels of a controversial chemical meant to kill bacteria spike in the bodies of young children after they brush their teeth or wash their hands, according to a new study.

U.S. manufacturers are phasing triclosan out of hand soaps after the Food and Drug Administration banned it effective last year amid concerns that the compound disrupted the body’s hormone systems. It remains in Colgate Total toothpaste, some cleaning products and cosmetics. Health experts say exposure is best avoided for babies in the womb and developing children.

The latest study, published in the journal Environmental Science & Technology, is one of the first to show that children’s levels rise through their first few years of life. Hand washing and teeth brushing have speedy, significant impact on levels, the researchers found.

“There’s very little data on the exposure in those first years of life,” said the senior author of the study, Joe Braun, an assistant professor and researcher at Brown University. “There are a lot of behavioral changes in the those years, and environmental chemicals can play a role.”

Braun and colleagues tested the urine of 389 mothers and their children from Cincinnati, collecting samples from the women three times during pregnancy and from the children periodically between 1 and 8 years old.

They found triclosan in more than 70 percent of the samples. Among 8 year olds, levels were 66 percent higher in those that used hand soap. And more washing left the children with higher loads—those who reported washing their hands more than five times per day had more than four times the triclosan concentrations than those washing once or less per day.

Children who had brushed their teeth within the last day had levels 2.5 times higher than those who had a toothpaste-free 24-hour span.

“It’s a thorough, well-done analysis,” said Isaac Pessah, a researcher and professor at University of California, Davis, who was not involved in the study. “Given the high concentrations [of triclosan] in personal care products, you’re seeing that the concentrations in the end user are also quite high.”

Braun said the levels of triclosan rose as the children aged, eventually leveling off. “Their levels were almost to moms’ levels by the time they reached 5 to 8 years of age.”