Hydroxyl Radicals in E-Cigarette Vapor and E-Vapor Oxidative Potentials under Different Vaping Patterns

Chem Res Toxicol. 2019 Jun 17;32(6):1087-1095. doi: 10.1021/acs.chemrestox.8b00400. Epub 2019 Apr 23.


Available studies, while limited in number, suggest that e-cigarette vaping induces oxidative stress, with one potential mechanism being the direct formation of reactive oxygen species (ROS) in e-vapor. In the present studies, we measured the formation of hydroxyl radical (OH), the most destructive ROS, in e-vapor under a range of vaping patterns (i.e., power settings, solvent concentrations, flavorings). Study results show that increased power output and puff volume correspond with the formation of significantly higher amounts of OH in e-vapor because of elevated coil temperature and oxygen supply. Vegetable glycerin (VG) e-liquids generated higher OH levels than propylene glycol (PG) e-liquids, as did flavored e-liquids relative to nonflavored e-liquids. E-vapor in combination with ascorbic acid, which is an abundant biological molecule in human epithelial lining fluid, can also induce OH formation. The dose of radical per puff associated with e-cigarette vaping was 10-1000 times lower than the reported dose generated by cigarette smoking. However, the daily average OH dose can be comparable to that from cigarette smoking depending on vaping patterns. Overall, e-cigarette users who use VG-based flavored e-cigarettes at higher power output settings may be at increased risk for OH exposures and related health consequences such as asthma and chronic obstructive pulmonary disease.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • E-Cigarette Vapor / chemistry*
  • Electronic Nicotine Delivery Systems*
  • Flavoring Agents / chemistry*
  • Humans
  • Hydroxyl Radical / analysis*
  • Ligands
  • Oxidation-Reduction
  • Vaping*


  • E-Cigarette Vapor
  • Flavoring Agents
  • Ligands
  • Hydroxyl Radical