My ten year old is a chewer as well, although he has never taken to chewing his hands, which some professionals tell me is a shame, actually, since a hand "is always there," lol. ANYWAY, I do notice that the level of chewing does have a relationship to stress, but my son also uses chewing to help him focus. He can't concentrate on homework unless he is chewing, so we've learned to provide carrots or straws for him to chew on while he is working.
My son has been diagnosed as having mild Aspergers and sensory issues. I understand chewing a very common stim for children on the spectrum. I had assumed that the chewing was directly related to these diagnosis', so it's been interesting to read that many people do it without having such issues.
I think the core thing to do is to decide what chewing is OK, and what chewing is not OK. If it calms your son, it isn't really productive to try to stop the habit, but it CAN be channeled. When my son was heavily into sleeve chewing, we started to put him in short sleeves only. When we got worried about the excess pencil chewing, we learned to provide him straws or food to chew on instead. And so on.