Cigarette tar causes single-strand breaks in DNA.

The results of this study demonstrate, for the first time, that cigarette tar causes DNA damage. Incubation in vitro of phage PM2 DNA with aqueous extracts of cigarette tar results in the introduction of DNA single-strand breaks. The effects of protective enzymes and radical scavengers indicate the involvement of active oxygen species. Although the semiquinone components of tar reduce dioxygen forming superoxide radicals and hydrogen peroxide, our results suggest that hydroxyl radicals formed via metal catalyzed decomposition of hydrogen peroxide are ultimately responsible for the DNA lesions. Our results also suggest that the metals in tar are reduced by the semiquinone components of tar and by superoxide at comparable rates.