E-cigarettes are battery-operated devices that can look like a real cigarette or pen. Some with refillable tanks look a bit different. There are hundreds of brands, and they're sometimes marketed as a way to get your nicotine fix without the danger of cigarettes.
They all work the same basic way:
They have containers filled with liquid that's usually made of nicotine, flavorings, and other chemicals.
A heating device turns the liquid into vapor that you inhale when you take a drag.
Using an e-cig is called "vaping."
Are They Safe?
Most contain the chemical nicotine, which is addictive. When you stop using it, you can go into withdrawal and feel depressed and crabby. Nicotine isn't good for people with heart problems. And some initial research shows it may hurt your arteries.
It can also:
Harm the developing brains of kids and could affect memory and attention.
Damage unborn babies. Pregnant women shouldn't use anything with nicotine.
But the concerns go beyond nicotine alone.
Some brands contain chemicals including formaldehyde -- often used in building materials -- and another ingredient used in antifreeze that can cause cancer.
Flavors in e-cigs also raise red flags. Some use a buttery-tasting chemical called diacetyl, which is often added to foods like popcorn. When it's inhaled, it can be dangerous.
"Diacetyl is a well-known harmful chemical, which, among other things, causes a lung disease called 'popcorn lung,'" says Erika Sward, assistant vice president for national advocacy at the American Lung Association.