Invited Commentary: The Epidemiology of Electronic Cigarettes and Reproductive Health Begins.

Harlow et al. (Am J Epidemiol. 2021;190(3):353-361) are among the first to tackle the complex subject of electronic cigarette use and reproductive health, focused on fecundity but pertinent to the full spectrum of reproductive health concerns. Despite extensive documentation of the health harm from tobacco use and a shared exposure to nicotine, electronic cigarette (e-cigarette) users have a markedly different exposure profile. Because e-cigarettes might help to curtail or eliminate tobacco smoking, the health comparisons of interest for e-cigarettes should include cigarette smoking as well as no use of such products. These researchers confront significant methodological challenges in the study of reproductive health effects of e-cigarettes: addressing confounding with little information on the characteristics of e-cigarette users, a complex connection between e-cigarette and tobacco use, multiple and poorly understood exposure to e-cigarette vapors, and lack of a standard method for quantifying exposure. Evidence is urgently needed to inform regulation and individual decisions regarding the use of this potentially harmful product that might well entice new users of nicotine, some of whom progress to tobacco use, but that also has the potential to enable otherwise recalcitrant smokers to substitute a less harmful product.