I'm not sure how much I can help. I do get somewhat itchy cheeks, mainly because I seem to get a bit of breakage there (which I think causes more itching than regrowth of plucked hairs). When they itch, that is usually about time to run the epilator again, even if only for a few minutes on them alone. That usually will stop most of it really fast. I epilate because shaving is just frustrating for me. I get cuts, and itching much sooner, it's just bad all around.
I epilate everything. The scrotum you can do some of it if you pull it tight (VERY tight, and be VERY VERY careful! I can do about 2/3rds of it, lower half and sides), the rest I hand pluck. Use slow speed if you have it because if you catch something, you don't want it at full speed and power. I have been manually plucking that for years.
For the anus, find a chair and desk/table you can really lean back in and prop your feet up on and spread em'
(make sure you are clean too obviously). Again use low speed, start off going across the crack and perineum. Don't go with the perineum as you can really aggravate the ridge. You need to go across that. After that slowly work your way more and more inward. Depending how how you flex the muscles, and pull here or there, you can get various areas better. Just kind of feel your way around, don't just start running it across things. If you have a good mirror an occasional check helps so you aren't going over the same places over and over again causing irritation. A finger also works. Go slow, and very, very light pressure if any. Initially try not even touching the skin then work your way in. Also, a good cleaning once you are done. If you have any hemoriods, you may want to steer clear of it.
I do this at least every 2 weeks, preferably 1. Things don't get very long or thick. Both of which makes it more painful.
BTW Nicky, do the scrotum. Really. It changes all sensation there for the better. I did it yeara ago, I don't even remember why, but OMG it was so nice.
