One of the more hazardous forms of BDSM, breath control (or erotic asphyxiation) is just how it sounds - controlling the amount of air available for somebody to breathe. ALL OF THESE ACTIVITIES ARE DANGEROUS. THEY SHOULD NOT BE ATTEMPTED. If anything goes wrong, it can easily be fatal or cause serious brain damage, and play is discouraged unless you know exactly what risks you are taking, and even then, you are fully liable for your own risks.

There are many different means for breath control, and first we will look at how the air gets from outside to inside the lungs.

Air passes in through the nose and mouth, through the windpipe, and into the bronchia and lungs. This flow can be stopped or restricted in three ways:

• Blocking the nose and mouth - this can be with a rubber mask, or gas mask with controllable tubes attached; or simply by holding the hand over the mouth and nose. A particularly sensual form is to hold the nose of your partner, and kiss them deeply.
• Blocking the windpipe from the outside - pressure on the throat can be applied with the hands or with tight collars or ropes. Most auto erotic deaths occur this way. Very dangerous indeed. Collars have been developed which are supposed to remove the constriction on fainting - but it could already be too late.
• Blocking the windpipe from the inside - very deep fellatio will cause the windpipe to be blocked completely and breathing will not be possible, even through the nose.

Next, we look at what we can do with the air entering the lungs. It is possible to completely cut off the supply; but other options are available. Rebreathing hoods are a closed system, and have an inflatable bag, into which the air expelled from the lungs goes. On breathing in, this air is re-inhaled. Since the lungs are not very efficient, there is still oxygen in the mixture, but less on each breath.

Another device again is a double-headed hood. This way, two people breathe into each other's lungs. Not only do they get used air, low in oxygen, but they have to synchronise their breathing to get any air at all.

Some people, rather than cutting off the air supply, like to simply pollute it. This is often done by introducing poppers into the air supply of a gas mask.

Once again, I have to reiterate: These activities are extremely dangerous, and should not be attempted in any circumstances.