DISCLAIMER: I am *not* an expert in blood play. Please, please, please do proper research before trying something like this.
I was asked by one of my Twitter followers to write about blood play. While this is not one of my kinks (I'm a bit squeamish about blood), your kink doesn't have to be my kink.
So what is blood play? According to Peter Masters, a BDSM expert, blood play is any form of BDSM play in which bloodletting is either common or expected. Some of the activities that might produce a side effect of blood play are flogging or caning, but also more extreme types of play such as cutting/knifeplay, needle play or piercing. The latter three, of course, are more likely to produce blood, as the object in this play is oftentimes that very thing. Oftentimes you can do a flogging or caning scene without introducing blood into it at all. But if blood is what you want, these activities can be done to a point that blood is introduced.
I hope I don't have to tell you all that if you're going to play with blood you need to have a LOT of communication and negotiation ahead of time, right? RIGHT? And you don't do something like blood play unless you totally, absolutely trust the other person in the scene. Trust comes with time. People have to earn trust and if someone tells you anything different, run, don't walk, in the other direction.
If you follow the link above to Peter Masters, he explains some of the safety protocols (like latex gloves) that should be used with blood play. The always-informative Leather n Roses blog also has an excellent post on blood play: http://www.leathernroses.com/generalbdsm/vergarabloodplay.htm. Safety is always paramount in BDSM, but especially with any form of edgeplay or extreme play.
*stepping off soapbox*
How common is blood play? I'm not sure, honestly. I know there are people out there who do it, but it's not nearly as common as, say, impact play (spanking, paddling) or bondage. Many public clubs don't allow it because of the health risks, so you're more likely to encounter it at a private party or in someone's home.
NOTE: If you're not squeamish and you want to see one interesting example of blood play, check out this site: http://bdsmforbeginners.blogspot.com/2009/07/ms160-watches-blood-cupping-scene.html?zx=860febf3d0979c82