Bleaching does not make enamel whiter, instead it gets rid of all the stain
on the
teeth you may have acquired from drinking tea,
coffee, soda, smoking and eating foods with color additives. Over-bleaching may even cause your teeth to become see through (pretty freaky sight if you ask me). Thankfully this sort of side effect passes after 24 hours.
Now most of the damage done by bleaching products are to: soft tissue - gums, dentin - located beneath enamel.