how long does it take for arm hair to grow back after shaving??

I'd say at least a month on average.

I would say at least 6 - 8 weeks..depending on how long the arm hair was in the first place. My husband had a tattoo done on his wrist 3 1/2 weeks ago and it's got a ways to grow yet before being not noticably missing.

His hair is a light brown...if yours is lighter, it won't be as noticable growing in.

quincy