After a full first clearance, with a good practitioner, you would expect to have a bare upper lip for 7 to 21 days before the next batch of hairs started becoming noticeable to the casual eye. The treated hairs would NOT come back at all, not thicker, or thinner. What you do need to understand is growth cycles, and the fact that while you may only have 5 to 10 hairs per square inch in that space, you have at least 1,000 follicles per square inch regardless of how many are currently growing hairs. If something starts recruiting follicles to grow hair in the future, it would have as many follicles to choose from as you currently have now, that are NOT growing hairs, and therefore won’t be treated with electrolysis.
for more info, check out this link