Mercury
Using mercury to fade brown spots can cause mercury poisoning. Although mercury is banned in U.S., unfortunately, almost 1 out of every 4 Asian made skin lightening products sold in the U.S. contain this highly toxic substance.
As a heavy metal, mercury can be toxic to your body. Using it can leave you with kidney, psychiatric, and neurological disorders. If you are pregnant, you can pass the mercury to your unborn baby.