Does your kid use tobacco? It’s more likely than you might think: Nearly 1 in 3 middle- and high-schoolers say they’ve tried a tobacco product.

And when youths opt for ­e-cigarettes, a new study suggests, parents are much less likely to know. The study, published in the journal Pediatrics, uses data from the long-term Population Assessment of Tobacco and Health study. Researchers from the University of California at San Francisco analyzed whether parents knew or suspected their children used tobacco and looked at how household rules affected kids’ tobacco use.

Between 2013 and 2017, most youths between ages 12 and 17 reported using both cigarettes and other tobacco products such as e-cigarettes, hookahs or chewing tobacco. In 2018, vaping outpaced traditional cigarettes.

When study participants reported they only vaped — as a majority did in 2018 — their parents were much less likely to know. About half as many parents whose kids only vaped suspected or knew that they did, compared with 69 percent of kids who smoked traditional cigarettes.

Given that about 3.6 million youths vape, that lack of awareness is a big problem. In 2020, the CDC reports, approximately 1 in 5 high school students and 1 in 20 middle-schoolers uses e-cigarettes.

The study’s picture of vaping teens and clueless parents is sobering, but it also offers a potential workaround. Researchers found that youths who lived in homes with strict rules were far less likely to start using tobacco than their peers in permissive homes.

The kinds of rules mattered: When teens or tweens lived in homes that forbade all tobacco for all residents, they were less likely to use it than kids whose parents simply talked to them about tobacco.

The researchers suggest it comes down to making tobacco taboo in all its forms — for everyone in the home. “Creating tobacco-free home environments is one approach parents can use to set norms and expectations about tobacco use,” says Tsu-Shuan Wu, a dentistry student at UCSF and the paper’s co-author, in a news release. “Raising parental awareness should be part of overall guidance and tobacco-prevention support.”