Although electronic cigarettes are promoted as a safer alternative to smoking tobacco, evidence continues to mount that they carry their own set of risks. The most recent study, which will be presented at CHEST World Congress later this month, found that e-cigarettes have an immediate effect on pulmonary function.

Researchers studied 54 young cigarette and e-cigarettes smokers; 27 had mild controlled asthma and the others were healthy. After smoking e-cigarettes, measurements of airway obstruction and inflammation were worse in both groups, but were more severe in asthmatics.

"These results show that as it happens with cigarette smoking, e-cigarette smoking has more deleterious short-term effects on asthmatics compared with healthy smokers," said Dr. Andreas Lappas of the Hellenic Cancer Society, Athens, Greece.

"Additionally, this research adds to the growing body of research pointing to the dangers of e-cigarettes. Especially for asthma, further research is needed in order to assess the risks of long-term e-cigarette use."

Other studies have found electronic cigarettes to be just as dangerous as traditional cigarettes. A Harvard study found that of 51 e-cigarettes tested, at least one toxin was found in 47 of them, and 75 percent contained diacetyl, a chemical linked to a severe respiratory disease called bronchiolitis obliterans or "popcorn lung." Even more frightening, the amounts of diacetyl found in 39 of the e-cigarettes contained amounts higher than the laboratory was capable of measuring.

A study from the Veterans Affairs San Diego Health System found that e-cigarettes damaged DNA in ways that could cause cancer and cell death. "Based on the evidence to date," says lead researcher Dr. Jessica Wang-Rodriquez, "I believe they are no better than smoking regular cigarettes."

The number of Americans using electronic cigarettes is growing rapidly. A Reuters poll found that U.S. adults using them rose from 2.6 percent of the population in 2013 to 10 percent in 2015.