The Centers for Disease Control and Prevention reports that as many as 2.4 million teens use electronic cigarettes, and that 70 percent of middle and high school students have been exposed to e-cig advertising.

There’s renewed attention to the potential health risks of e-cigs, but overlooked is the danger to the hearing of young people. A study published last June confirmed confirmed the adverse effects of smoking on the inner ear of adolescents.

While e-cigarettes do not produce carbon monoxide, tar and other toxic chemicals associated with regular cigarettes, most include nicotine. While nicotine’s toxic effects on the ear are not fully understood, it is well established that nicotine reduces oxygen in the bloodstream and decreases blood flow.

In the ear, oxygen is essential to cochlear hair cells, which convert sound waves into electrical impulses the brain can understand. Decreased blood flow and lower oxygen levels can damage those hair cells, resulting in hearing loss.

There is, however, a more pernicious hazard that makes e-cigarettes an even greater risk to hearing than traditional cigarettes. Unlike regular cigarettes, which have a fairly consistent concentration of nicotine, many electronic cigarettes rely on refillable tanks that contain liquid laced with different flavors (like bubble gum, marshmallows and gummy bears) and different nicotine levels that the user can customize.

Given how addictive nicotine is, the ability to alter the nicotine concentration means that abuse is more likely to occur, particularly among adolescents who seek higher doses, creating an even greater risk of hearing loss.

The health hazards of smoking are well-known. The good news is that U.S. smoking rates have been steadily dropping. However, e-cigarette use has been rising exponentially. The CDC says that e-cigarette use among teenagers tripled between 2013 and 2014.

The effects of e-cigarettes are less known, but nicotine – regardless of whether it is inhaled in smoke or in vapor – presents a significant risk to hearing. More research is needed to determine the full impact.

But teens who are lured into using e-cigarettes thinking they’re not as dangerous as tobacco, need to understand that they’re trading the devil they know for the devil they don’t.