Mercury pigments are most commonly associated with skin reactions. These reactions may occur years after you get your tattoo. Often the metal alone doesn’t cause a problem, but it is when the pigment is exposed to cross reactants that a reaction can occur. Chemicals like the preservative thimerasol (used as a preservative in contact lens solutions and eye drops), mercurochrome, and some vaccines, may cause a reaction in your tattoo. If you think you have a thimerasol allergy, you may want to explore non-metallic pigments. Also, some organic compounds have been known to cause phototoxic reactions when exposed to sunlight.