It’s not anti-tobacco advertising that is making kids smoke less, but rather it’s a mix of smoke-free zones, higher taxes, and other initiatives that is curbing teen smoking. In a new study published in JAMA Pediatrics, researchers examined the factors behind recent drops in smoking among youths.

The researchers analyzed teenagers who were aged 12 to 18 in 1997, then tracked them for 11 years to see how their smoking habits changed over time. During this time period, legislation surrounding smoking in the U.S. transformed into banning cigarettes from indoor places to public parks and even sidewalks — and the taxes on cigarettes were increasing as well.

Back in 1997, no teenager had a 100 percent probability of being under a 100 percent smoke-free workplace law, and only 11.6 percent had a 100 percent probability of being covered by a smoke-free restaurant law and smoke-free bar law. Ten years later, however, 27.3 percent of the participants had a 100 percent probability of being covered by a smoke-free workplace law, and the other numbers had increased to 43.3 percent and 36 percent, respectively.

They found that smoke-free environments reduced the risk of teen smoking by one-third, and also protected nonsmokers by keeping them free from secondhand smoke. In addition, they found that young people living in states with 100 percent smoke-free bar laws were actually 20 percent less likely to be smokers, and smokers in these states smoked less on average than those who lived in states without these laws.

“Because smoking initiation typically occurs before youth enter the workplace, smoke-free workplace laws likely affect smoking initiation by showing kids that adult smoking norms reject smoking,” Anna Song of the UC Merced Health Science Research Institute said in the press release. “The effects of smoke-free laws are similar or larger than other determinants of smoking, including age, sex, race/ethnicity, and poverty level.”

Since 1975, the percentage of 12th graders in the U.S. who smoke cigarettes daily has dropped from nearly 30 percent to under 7.5 percent in 2014, according to the Department of Health and Human Services (HHS). The percentage of smokers in 10th grade, meanwhile, has fallen from around 20 percent in 1996 to under 5 percent in 2014. And a new report from the CDC found that smoking rates in general in the U.S. are at an all-time low.

There are a lot of factors responsible for the decrease in teen smoking rates in recent decades. For one thing, copious amounts of research has proven that smoking causes lung cancer, among other chronic diseases, and it’s likely young adults are old enough now to know at least one friend or relative who has succumbed to tobacco’s health consequences. E-cigarettes are considered a possibility in ending smoking, but not enough research exists yet to identify whether they’re helpful — or if they form as a “gateway” into smoking.

Ultimately, what the recent study concludes is that it’s smoke-free places that have the biggest influence over preventing teens from smoking. If you can’t bum a cigarette off someone at work, in the park, or at a bar — you’re probably less likely to go out of your way to shell out a lot of money for a pack at the deli.

“Smoke-free workplace laws have the most powerful effect on smoking initiation, equivalent to the deterrent impact of a $1.57 tax increase,” Stanton Glantz, a professor of medicine at UCSF, said in the press release.

Source: Dutra L, Neilands T. JAMA Pediatrics. 2015.