How safe are electronic cigarettes using propylene glycol as the "vapor" for asthmatics? better than real cigarettes?

Electronic cigarette: Always difficult to tell what will be an irritant to an asthmatics. Probably one if the biggest benefits of an electronic cigarette is that it precludes exposure to some of the carcinogens found in tobacco products. Also reduces negative side effects that nicotine has on the cardiovascular/cns/respiratory/ other organ systems.