Frequent travelers know that in the event of changes in cabin air pressure, one must put on his or her own oxygen mask before helping others. But have you ever wondered what's actually inside that thing?

We wondered too, after the fine folks at io9 pointed out that oxygen masks can be made with chemicals that you'd never want to breathe anytime soon. We asked our trusty travel experts to put things in plane terms.

The air in your "oxygen mask" starts out not as oxygen, but as a bunch of other chemicals.

Yes, those chemicals become breathable oxygen, but they don't start out that way. Your "passenger service unit" actually uses a cocktail of chemicals, which are usually stowed in an overhead oxygen generator.

If cabin pressure drops, either the flight crew or an automatic trigger releases the masks. When you pull down on the mask, you're releasing those overhead chemicals -- commonly sodium perchlorate and an iron oxide -- and letting them mix together. The chemical reaction, or "burning," makes oxygen that flows to you. It also makes the overhead chamber REALLY hot, according to Arch Carson, an occupational health expert at The University of Texas Health Science Center at Houston School of Public Health.

"When you pull down on the mask, it'll generate a burning smell," Carson told The Huffington Post. "It's a bit like turning on a new oven." Woof.

...but don't worry; you can breathe it in safely.

"You might get some small bits of chemical dust," Carson said. "But it's way better than the alternative, which is passing out due to lack of oxygen."

Your oxygen will last only about 15 minutes.

Passenger oxygen masks typically provide enough air to last 12 to 20 minutes. However, this is usually plenty of time for the pilot to get the plane to a safe altitude where masks aren't needed anymore, according to Air Force flight surgeon Dr. Gregory Pinnell.

"Pilots can get down much more quickly than it takes to run out of oxygen," he said. "They know the situation."

But it's crucial to put your mask on first, and to do it fast.

Low cabin pressure triggers a mask drop. And when oxygen is that scarce, it's important to fix things fast.

If you don't put your mask on within 30 seconds of a pressure change, you risk passing out, Pinnell said.

"Once the cabin loses oxygen, passengers can become lightheaded and disoriented... and then lose consciousness," adds air travel expert George Hobica. "It's important to act quickly."