The question may become more common as electronic cigarettes become more popular. The answer, however, remains elusive. Etiquette aside, the health effects of inhaling nicotine vapor are largely unknown. In the meantime more research is clearly needed.
The small studies that have been done so far hint at both pros and cons; one found that smokers cut back on real cigarettes after trying the electronic kind, while another found particles of metal and silicates in e-cigarette vapor that could cause breathing problems.
The FDA in the United States will begin to regulate e-cigarettes later this year after a federal judge ruled that it couldn’t classify them as medical devices (because they deliver a drug, nicotine), the FDA will regulate them as tobacco products (because nicotine is derived from tobacco). Unlike regular cigarettes, however, e-cigarettes are not known to be lethal. Wariness is warranted, but it’s safe to assume that their vapors are not nearly as dangerous as tobacco smoke.