My son is a teenager with fairly typical acne.  It has been suggested by a manual medicine practioner that his bowels are not functioning as efficiently as they should -- he has recommended some pro-biotics (v. broad spectrum, high quality a must!) to help get this sorted.  He has just started taking them and I'll keep you posted here on his progress.  He has been told to expect his skin to get worse as a reaction and then to improve dramatically.  Fingers crossed!  He is also going to try some homeopathics -- these have not yet been prescribed though.  More on that later.