Does anyone know what causes stretch marks? I've got some small ones starting on my outer pecs, almost in my armpit there. I've gained 15 lbs in the gym this year and these are the first I've seen, but I know guys who are skinny and have them, and I know girls who are skinny and have them on their ass or tits. What causes them? What have you guys found keeps them from progressing, or even reverses them?
Thanks for input!
Montgomery