Among high school teens in the United States, about 22 percent said they had used e-cigarettes, known as vaping, in the preceding 30 days, according to research that tracked a nationally representative sample of 8,660 10th- and 12th-graders. Only 7 percent of the teens said that vaping was a daily habit, but 41 percent said they have vaped at some point. The research, which was published in the journal JAMA Pediatrics, says that the rapid increase in teen vaping from 2017 to 2019 slowed somewhat in 2020, which it attributes to a rise in the legal age to buy e-cigarettes and to bans on e-cigarette cartridge flavors that teens favor. Still, the prevalence of vaping among teens and young adults sparks concern because of the health risks associated with it, which exposes the lungs to addictive nicotine and a variety of chemicals. For instance, two new studies, published in the journals Tobacco Induced Diseases and PLOS One, report a link between vaping and mental fog, with those who vape having more trouble concentrating, remembering and making decisions than their peers who neither vape nor smoke. In addition, people who vape, compared with those who do not, are 43 percent more likely to develop a respiratory disease, including increased risks of chronic bronchitis (33 percent), asthma (31 percent), emphysema (69 percent) and chronic obstructive pulmonary disease (57 percent), according to research published in JAMA Network Open that included 21,618 nationally representative adults. Vaping has been linked in several studies to an increased risk of covid-19 in young adults. And a new study in the journal Addictive Behaviors finds that youths who vape are nearly three times more likely to take up cigarette smoking and more than twice as likely to try smokeless tobacco as are those who do not use e-cigarettes.