There are many factors that influence the answer to this question, such as settings used by practitioner for any given type of hair. For example higher electric currents maybe selected if hair is dark in colour, course in size and strongly rooted, whereas finer white hairs maybe require a lower electric current to release and kill the regrowth cells.
Ingrown hairs can also prove to be stubborn as needles may not reach the hair bulb on first attempt due to hair distortion. In such a case, a second and subsequent attempts may be required should the hair start to grow again during a subsequent hair growth cycle. Electrolysis is approved for permanent hair removal by the US Food and Drug Administration (FDA), so eventually all hairs are expected to leave the body or face for a hair-free appearance.