Why do people breathe into a paper bag when hyperventilating ?

Question

Why do people breathe into a paper bag when hyperventilating ?

Answer 1

Hyperventilating throws off the CO2 and oxygen levels in your blood, causing the brain's involuntary breathing reflex to be thrown for a loop.

Breathing into a bag causes you to rebreathe CO2 instead of more oxygen; it helps regulate blood gas levels and return your breathing to normal.

Answer 2

When people hyperventilate, many of the subsequent symptoms are from alkalosis due to blowing off too much carbon dioxide. The paper bag thing allows one to re-inhale a little of the carbon dioxide. Of course, it isn't nearly so effective as popping a couple of benzo's, but it can help.

Answer 3

If you breathe too fast, you are getting rid of carbon dioxide from the blood faster than normal. You might think this is a good thing, since CO2 is a waste product. However, the amount of CO2 in the blood affects its pH - too much CO2 makes your blood too acid, too little CO2 (like if you have a panic attack and hyperventilate) and your blood gets too alkaline. That has lots of other effects, like making you dizzy and tingly and faint etc. If you breathe into a paper bag, you are not breathing in fresh air each time - you are breathing back in some of the air you just breathed out, so you are breathing in more CO2 than normal. This means you don't get rid of it so fast and the blood pH can get back to normal. And because that makes people feel less dizzy and weird it helps them to calm down.