Hi there, Your sons condition sounds exactly like what myself (35), my daughter (8), nieces (11 and 8) and other family members suffer from called Keritosis Pilaris, where your body produces too much keratin (the stuff  found in our hair and nails ) I have it on the back of my thighs and back of arms. My daughter has it in those places and her buttocks. My GP also has this condition and tells me that there is no cure for it and that most adolescents will out grow it.  I developed it at about 9 years old and haven't outgrown it yet. I have a friend who is an RN and she tells me that too much keratin production is due to a vitamin A deficiency but I have not confirmed that yet. The only thing I have found that helps is to very gently exfoliate the area everytime I bathe or shower with an exfoliating mitt or pumice stone and then use a good moisturizer afterward that doesn't have any nasty chemicals in it ( especially important for young developing bodies).   It can be painful when infamed. My daughters arms sometimes get so prickly that it catches on her clothing and irritates her.   best of luck, Karen