While it might seem like introducing unidentified “vapors” into your lungs via an electronic cigarette can in no way be healthy, there is still a lack of consistent evidence. There are more than 500 brands of e-cigarettes, making it difficult to gather data.

However, information presented at the 17th World Conference on Lung Cancer suggests that there are, indeed, a number of respiratory problems directly related to the use of e-cigarettes and the unregulated chemicals in the fluid/vapor.

While some cigarette smokers use e-cigarettes as an aid to quitting tobacco products, 8 out of 10 vapers continue to smoke tobacco products, adding the unknown on top of an already dangerous habit.

E-cigarettes deliver a vapor that consists largely of propylene glycol, which is an active ingredient in antifreeze, and glycerin, in addition to nicotine with more than 8,000 flavors containing chemical additives.

Many of the flavors are approved for oral intake, but not for inhalation as a vapor. For example, diacetyl, which is found in 75% of e-cigarette samples, has been approved for safe use as a food sweetener, but is known to cause bronchiolitis obliterans in workers exposed to it via inhalation. Fluid/vapor extract is shown to cause changes in lung tissue cells and inflammatory changes.

A study of more than 45,000 Chinese students found e-cigarette use to be associated with significant increases in respiratory symptoms, physician diagnoses of asthma, chronic cough, mucus production and bronchitis symptoms.

While there is much to be learned about the effects of e-cigarettes on long-term health there is already plenty of evidence that using them is harmful. Your best bet is not to smoke anything.