Pennsylvania may raise tobacco sales age to 21. Science says that could slash smoking rates.

Raising the legal age for tobacco purchases from 18 to 21 significantly decreases smoking among young adults, two new studies from the Yale University School of Public Health suggest.

Pennsylvania lawmakers are expected to discuss the issue when the legislature reconvenes in September.

Bills to raise the minimum age to purchase tobacco products from 18 to 21 — often called tobacco-21 laws — were introduced in the House and Senate last session, but have yet to make it to the floor for voting.

If they pass, Pennsylvania will join 17 states in requiring people to be 21 to buy cigarettes or other tobacco products. Delaware recently made that move. New Jersey’s law has been in effect since 2017.

Public health experts say such laws are crucial, given that nine out of 10 smokers start by age 18, and 99 percent start by age 26.

The two recent studies found that states and localities that have tobacco-21 laws have lower rates of smoking among young adults than areas with a lower minimum age.

“Not only do these laws seem to work, but they’re influencing the kids most at risk,” said Abigail Friedman, a coauthor on both studies and assistant professor at the Yale School of Public Health.

The first study, published July 25 in the journal Addiction, compared rates of smoking among 18- to 22-year-olds in states and large cities with tobacco-21 laws with areas without such laws.

Researchers analyzed data from 1,869 young adults who had tried cigarettes at least once before, as those individuals are most at risk of becoming regular smokers.

They found that 18- to 20-year-olds living in an area that had raised the age to legally buy tobacco products showed a 39 percent drop in regular smoking. The drop was even greater — about 50 percent — among those who had close friends who smoked when they were 16.

“The laws are not just reducing the behavior of individuals,” Friedman said, “but they are reducing the behavior of friends, and that creates a feedback loop, because what your friends do affects you, especially as a young adult.”

Researchers also looked at changes in smoking among 21- and 22-year-olds who would not have been affected by the tobacco-21 laws, but would have been influenced by other local factors like cigarette taxes, community attitudes toward smoking, and tobacco advertising. They did not find a reduction in smoking among the older age group, which suggests the tobacco-21 laws are specifically driving change for younger adults, Friedman said.

The second study, published July 26 in the journal Nicotine and Tobacco Research, supported these results.

It focused on the effect of county, town, and city laws raising the tobacco sales age to 21.

Researchers analyzed smoking rates among 18- to 20-year-olds in metropolitan/micropolitan statistical areas (MMSA), or clusters of adjacent counties with an urban center of at least 10,000 residents.

They found that between 2011 and 2016, the average smoking rate dropped more significantly among 18- to 20-year-olds living in MMSAs with at least one local tobacco-21 law than those living in areas with no tobacco-21 policy. The reduction was equivalent to a 10 percent decrease in smoking for that age group.

“This shows us that local laws work,” Friedman said.

Currently 16 states without tobacco-21 laws, including Pennsylvania, have preemption policies that prohibit towns and cities from raising the minimum legal age for tobacco sales above the state’s minimum age.

“Preemption laws are impeding public health,” Friedman said, even when residents support tobacco-21 laws. A CDC survey found three-quarters of American adults — including seven out of 10 smokers — support raising the minimum age of tobacco sales.

Neither study reported any findings on how tobacco-21 laws affect the use of electronic cigarettes, which have become more popular than cigarettes among adolescents and young adults in recent years.