A study into the impact of flavored e-cigarettes, on allergic airways disease, suggests that some flavors may worsen the severity of diseases such as asthma. For the first time a model of asthma was used to investigate the effect of a range of popular e-cigarette flavors, with and without nicotine.

The use of e-cigarettes has dramatically increased in the past few years especially among younger smokers—an estimated 9% of 18-24 year olds in the United States are current e-cigarette users.

Despite the suggestion they are a healthier alternative to tobacco cigarettes there is a lack of evidence in both animal studies and human data on the effect of e-cigarettes on lung function.

The results of a study led by researchers from the University of Technology Sydney (UTS), University of Vermont, US, and the Woolcock Institute of Medical Research, Australia, show that some flavored e-cigarettes, even without nicotine, may change how airways, affected by an allergic disease, function.

Dr. David Chapman, UTS researcher and lead author of the study published in Scientific Reports, said this was the first study to investigate the effects of flavored e-cigarettes with and without nicotine on allergic airways disease.

"This is especially important for those with respiratory disease, whom are vulnerable to the effects of smoking," Dr. Chapman said.

"The majority of e-cigarette smokers use flavored liquids but there is some evidence that flavor additives can be toxic when inhaled," Dr. Chapman said.

The researchers found some flavored e-cigarettes, even in the absence of nicotine, can worsen disease severity.

"The exact effects on features of asthma were dependent upon the specific flavor, suggesting not all flavoured e-cigarettes will have the same consequences on lung health," Dr. Chapman said.

In this study the flavor black licorice exaggerated airway inflammation whereas cinnacide had the opposite effect, suppressing airway inflammation. Additionally, cinnacide increased airway sensitivity and banana pudding flavor exaggerated the level of tissue scarring. All e-cigarette liquids containing nicotine suppressed airway inflammation, consistent with the known anti-inflammatory properties of nicotine.

The researchers didn't analyse the liquids directly, to confirm what they contained, however there is evidence from previous research that flavors categorised as "buttery/creamy" and "cinnamon," which likely include banana pudding and cinnacide, respectively, are toxic.

The researchers conclude that caution should be taken in promoting the use of flavored e-cigarettes to patients with respiratory disease such as asthma and that policy makers should consider restricting the use of flavoured e-cigarettes.