The popularity of e-cigarettes, especially among the younger population, has exploded in recent years.

In case you’re not aware, e-cigarettes are an electronic device that generally contains a battery, a heating element, and a place to hold a liquid that usually contains nicotine. When the liquid heats up, it can be inhaled into a user’s lungs and then exhaled into the air. This process is commonly referred to as vaping.

E-cigarettes became mainstream when they were marketed as a safer alternative to traditional cigarettes, despite containing a comparable amount of nicotine. The nicotine is burned in cigarettes, while it is only heated in e-cigarettes, which allegedly allows fewer toxins to be released into the user’s lungs.

However, the U.S. Food and Drug Administration (FDA) announced in August that they are seeking public input on a proposal that would add nearly 20 chemicals to its list of harmful ingredients found in tobacco products.

“As our oversight and scientific knowledge of tobacco products has evolved, so too should our requirements for manufacturers and importers to provide information about the chemicals or chemical compounds in their products that cause or could cause harm to users and nonusers,” acting FDA Commissioner Ned Sharpless said in a statement.

Among the chemicals that the FDA is considering flagging are ones that add flavor to the e-cigarettes. One is called diacetyl, which gives off a butter-like taste.

The FDA has long considered these chemicals safe to be added into food, but the long-term effects of these products being inhaled in aerosol form is unknown.

As more and more information comes out about the safety of e-cigarettes, you should talk to you doctor if you or young ones in your life are using these products.