It's been discussed before, but here is a quick lowdown so you won't have to search for too long on the threads

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Although it is true that hair grows at different rates, and treatment of any sort must be done in stages over a time period which allows for multiple treatments, you can still see more coarse hairs develop as time progresses. This could be older folicules which enter thier active state over time, but they could also be newer folicules developing.
If you have PCOS and elevated androgens, your fine vellus (thin light hairs) will be stimulated to become what are known as 'terminal' or darker coarse hairs. This can continue to happen if so long as the androgens are at work, which is why often following laser or electrolosis, individuals see hair appear to return again months later even after repeated treament. So what we're saying is that its often not old hairs returning, but newer terminal hairs developing.
With PCOS, often the hair isn't super dark or coarse, and it is often diffuse, which according to my laser tech makes for difficulty in treatment. In my case, years of waxing made for easier treatment, however, and we are having luck. It's been a year, and in most areas I have about 75-80% reduction, and more or less in others. I have another year in the plan, but we expect that soon it will be possible to cut back frequency.
The main thing is, get the hormones under controll, and you'll generally see less folicule development.
Best,
Cassy