According to Business Insider, at least 33 people have died from vaping-related lung injuries.
1,479 other "confirmed and probable" cases of vaping-related lung problems have been reported to the CDC.
Most of the lung injuries are happening to vapers who inhale THC, which is the ingredient in marijuana that gets people high.
But some injured patients say they only ever vaped nicotine. It's unclear what substance, or cocktail of substances, is causing the lung problems.
As patients all have some history with vaping, the CDC suspects there may be some kind of "chemical exposure" at work.
Lacking any clear culprit, the US Food and Drug Administration is telling consumers not to use THC vapes of any kind.