Then, if he were my son, I would consider it a sign of toxicity and suggest (since he's 16 and can't really be forced) that he increase the amount of live foods he eats every day. I would make sure he had access to plenty of pure water and then, if he will, I would have him do an herbal cleanse. At the very least, I would introduce green drinks into his diet for the added nutrition and for the alkalizing effects upon the body.