Very bad idea. Mercury is very toxic and harmful...even in small doses. Prolonged use over time could have effects such as cancer and birth defects.
Due to it's very toxic effects, mercury's use in cosmetic products is prohibited. But there is a restricted area, especially in eye cosmetics, where mercury is still used. Acoording to several scientific studies, the proper amount wouldn't have to exceed 65 parts per million. Mercury is used in cosmetic industry, as a preservative.