Hookah bars have popped up all over the place. But there’s a risk associated with smoking one you may not know about – carbon monoxide poisoning!

Most people assume smoking a hookah is better for you than cigarettes or cigars. But while the average cigarette smoker has a carbon monoxide level of 5 percent after a cigarette a smoker who’s toking on a hookah has a carbon monoxide level 6 times higher! The same levels you get when your house has furnace issues, after a house fire, or sitting in a car in a closed garage with the engine running! So why is that?

Because it takes about 10 or 15 drags to smoke a cigarette – while a person may take 100 hits off a hookah during one session.

And the Centers for Disease Control and Prevention say that, in a one-hour session, a person inhales up to 200 times the volume of smoke inhaled from a single cigarette. Also, because charcoal is used to heat the tobacco, it increases the levels of carbon monoxide.

And you may not know you’re suffering from poisoning because the symptoms are common – like fatigue and nausea. So you may just think you have the flu.  But in severe cases, poisoning can lead to a coma, and can even kill you. And even if it’s not that severe, over time, toking on that hookah regularly can lead to neurological damage.  That’s because it blocks oxygen from being absorbed by your blood. Even just smoking a hookah 10 or 15 times in a year can cause you to drop some IQ points – that’s according to Dr. Thomas Eissenberg from Virginia Commonwealth University who’s done extensive research on the pipes.

So if you think going to a hookah bar with friends sounds like a fun idea, just know what you’re getting into.