THE ANSWER
Yes, for the follicle treated. Once its growth cells are destroyed, that follicle does not produce hair again. What electrolysis cannot do is stop a different follicle, one that was previously dormant, from becoming active later. That is new growth rather than a treatment that failed, and it is the distinction that matters most on this page.
Why
The FDA and the American Medical Association recognise electrolysis as a permanent method of hair removal. That recognition is specific: it is about what happens to a follicle that has been successfully treated.
Successful treatment destroys the cells at the base of the follicle that produce hair. Those cells do not regenerate. The follicle remains as a structure in the skin, but it no longer grows anything.
What no hair removal method can do is control which of your other follicles become active in future. Everyone has far more follicles than they have visible hairs, and many produce fine, barely noticeable hair or none at all. Hormonal changes can prompt some of them to start producing coarse hair instead.
So someone with an ongoing hormonal driver, such as PCOS or the changes around menopause, may see new hairs appear years after finishing treatment. Those hairs are coming from follicles that were never treated, because at the time there was nothing there to treat.
This is why practitioners talk about occasional maintenance rather than a single permanent finish. The follicles treated are done. The picture can still change.
How do I really know the hair is permanently gone?
Because a treated follicle that no longer produces hair is not going to start again. What you cannot know in advance is whether other follicles will activate later, which depends on your own hormones rather than on the treatment.
Can new hair grow in a treated area years later?
Yes, from different follicles. It is common where there is an ongoing hormonal cause. It does not mean the earlier treatment reversed.
Will hormones make new hair grow after I finish?
They can. Hormonal changes are the usual reason previously dormant follicles start producing coarse hair. See hair removal for PCOS and menopausal facial hair.
Do I need maintenance sessions forever?
Not usually in any meaningful sense. Where there is an ongoing hormonal driver, most people find they need a short appointment occasionally rather than an ongoing course. That is a very different commitment from daily plucking.
What the evidence says
The FDA and the American Medical Association recognise electrolysis as the only permanent method of hair removal. Laser devices are cleared for permanent hair reduction, a different claim explained on permanent removal vs permanent reduction.
What to do next
Set your expectations by cause. If your hair growth has no ongoing hormonal driver, treating an area is likely to be a genuine finish. If it does, plan for occasional new hairs and an occasional short appointment, and judge the result against that rather than against never seeing another hair.
See gray, white and blonde hair removal or electrolysis consultation.