Smoking has long been associated with cancer and other deadly diseases. And while most warnings against smoking focus on the dangers of tar and carbon monoxide, a new report from the American Academy of Pediatrics puts the spotlight on nicotine—a chemical used in traditional cigarettes, e-cigarettes, hookahs, and all other tobacco products.

Nicotine is especially dangerous for children and adolescents, the report notes, who are increasingly turning to products like e-cigs and hookahs instead of traditional cigarettes.

“Nicotine is an extremely addictive substance, and the rapidly developing brains of children are particularly susceptible to it,” says Lorena Siqueira, M.D., M.S.P.H., recently retired director of adolescent medicine at Nicklaus Children's Hospital in Miami. Siqueira is the lead author of the report, published today in the journal Pediatrics, which provides a comprehensive review of the research on nicotine exposure in children and teens.

Long-term nicotine exposure has been linked with heart disease and an increased risk of stroke, the report notes. There’s also evidence that nicotine may increase the risk of oral, esophageal, and pancreatic cancer and make chronic kidney disease worse. It increases the long-term risk of osteoporosis and bone fractures, and has a negative effect on fertility in women and men. And early nicotine use is associated not only with addiction to cigarettes, but to drugs and alcohol, too.

Getting Hooked Early

Children are especially likely to become hooked on nicotine and to miss the signs of addiction when it takes hold, Siqueira says.

For example, in one study highlighted by the report, sixth graders who smoked only once per month displayed signs of addiction, such as symptoms of nicotine withdrawal and strong cravings between smoking sessions. Kids who went from smoking an occasional cigarette (less than once a month) to smoking once a month were 10 times as likely to end up dependent on cigarettes.

And the younger a child is when first experimenting with smoking, the likelier it is he will become addicted. According to another study cited by the report, an estimated two-thirds of kids who smoke in sixth grade become regular smokers by adulthood. By comparison, when children start smoking in 11th grade, 46 percent become adult smokers. Ninety percent of adult smokers started smoking before age 18, Siqueira notes.

“Youths do not recognize strong craving and withdrawal as symptoms of addiction,” Siqueira explains. “They think they can quit any time, but a lot of kids who are smoking infrequently already are dependent. They may even become addicted after just two or three cigarettes.”

Priming the Brain

The report highlights a few ways nicotine may have long-term effects on the pliable brains of adolescents.

“Nicotine can cause changes in your brain that can lead to abuse of other substances,” Siqueira says.

Nicotine may make the brain more susceptible to addiction by boosting concentrations of dopamine—the same feel-good chemical released in your brain during sex or when you’re in love. The report notes that excess dopamine is associated with increased reward-seeking behaviors, including gambling and drug use.

Nicotine may also “prime” the brain for addiction, though more research is needed to confirm this idea. Mice that were given nicotine were more likely to become addicted to cocaine, perhaps because the nicotine enhanced the expression of a gene associated with addiction, according to an earlier study published in the New England Journal of Medicine.

“Animal research isn’t always applicable to humans,” says Consumer Reports chief medical adviser Marvin M. Lipman, M.D., “but these studies help researchers understand how the brain reacts to nicotine.”

A New Generation of Smokers

In the U.S., the overall rate of smoking has declined, but youngsters are increasingly experimenting with alternative tobacco products, in large part because they see them as safe. The new report underscores that these users are still exposing themselves to great risk through the regular use of nicotine.

According to a report released earlier this month by the U.S. Surgeon General, the use of e-cigarettes surged 900 percent among high school students from 2011 to 2015. Last year, more than 3 million middle and high school students said they had used e-cigarettes in the past month.

E-cigarettes are sold in more than 7,760 flavors, including apple pie, cotton candy, gummy bear, and watermelon—flavors known to lure younger users. Once those younger users get hooked on nicotine, there's a good chance they'll be in for a lifelong habit.

It’s difficult to know exactly why teens who use e-cigarettes often use cigarettes later, but the American Academy of Pediatrics report suggests that “e-cigarettes may encourage, rather than discourage, the use of conventional cigarettes.”