There is actually a small risk of infection with electrolysis. Most every tech changes the needle with a new sterile needle for each patient, but there is human error. Everyone's skin is coated in bacteria, and wiping with a disinfectant mitigates it, but not eliminates. So the moment the needle is exposed to skin or whatever else, it's got bacteria that are normally on the outside of the skin about to get pushed into the skin. The needle is going to be in contact with capillaries at least a few times in a long session, small chances for bacteria to get a foothold and cause a problem either locally as a small boil or systemically. When done right on a healthy individual these are issues to scoff at, done wrong on a compromised individual could be disastrous, with a full spectrum of risk in between.