-How much water do you drink? You may not be flushing out something you're allergic to.
-Do you drink soda? If so, stop - you may be allergic.
- Do you drink wine/beer/alcohol - you may be allergic to them....
I had a boyfriend a ways back who had the skin writing thing, and it was a reaction to not drinking enough water, while simultaneously eating tons of Sugar and other bad foods and drinking a lot of lager. When he switched his eating./drinking habits for two months, his symptoms abated.