Vaping products containing nicotine cannot, by federal law, be sold to those under twenty-one. But some tobacco companies may have skirted the law by replacing nicotine in e-cigarettes with chemicals that have similar properties but unknown health risks. Researchers at Duke University Medical Center and Yale University wrote in JAMA that these nicotine analogs are not accurately disclosed on e-cigarette packaging. The research letter says these nicotine replacements, such as methyl nicotine, are included in flavored e-cigarettes which are preferred by young people and those vaping for the first time. Authors say it is not known what nicotine analogs do when they are heated and inhaled, and these questions should be answered before such products are allowed on the market.