When blood breaks down, iron is released and causes a
metallic taste in mouth. Bleeding can be from the gums, sinuses or nose. The
taste can get especially bad when someone has post nasal drip and the dried blood sticks to the back of the throat. If bleeding gums are the cause there is often bad breath associated with the bad taste.
Another uncommon reason for a metallic taste in mouth is due to small electric currents in the mouth.