My experience with needles is exclusively unerotic -- I get weekly injections. It's a rather thin needle, and it goes deep...deeper than I think it would with needle play. I have no scars whatsoever, and the bleeding is minimal, it's just a drop or two after you remove the needle.

As for needle play itself, I only have some second hand knowledge to offer because I read up on it a while ago when I was interested in the same thing So in addition to the precautions that have already been mentioned (disinfect the area, use sterile needles etc.) here a few additions:

- don't use the same needle twice. Once it has penetrated the skin and removed again it is no longer sterile. It's not really dangerous if you do, but it increases the chance of an infection.

- In addition to the normal sterile needles we have something called lancets available. These are basically very short needles that can't go deep. They are usually used to prick your finger for something like a blood-sugar test. So, in case you are concerned about going too deep or anything like that, it is impossible to do any real damage with those.

- As for the technique: Don't go deep into the tissue, particularly in the breast area. The breast tissue is apparently really sensitive and could be harmed that way. This means, try not to use a 90 degree angle when you are needling, but rather a flat angle so the needle only goes into the top layers of the skin.

- As for haematoma: Everyone who had a blood-test knows that although it's nothing dramatic haematoma happen rather quickly. That's of course nothing to worry about, but doesn't look nice nonetheless. In order to avoid the bruising you can compress the area in questions with whatever sterile thing you have at hand for a little while.

As said, this is second-hand knowledge, and I'm quoting from memory here. I haven't tried it so I can't vouch for the accuracy -- I hope it's helpful nonetheless