Women often swipe foundation or concealer over their lids to minimize darkness and to create a base for their shadows and liners. This is a bad idea.
First off, you never want to put anything on your eyelid that is not meant to go on the eyelid. The soft tissue and skin that make up the eyelid are sensitive and can be easily penetrated, so you should always be sure that whatever products you use on your eyes are safe.
Second, foundations and concealers are often creamy and luminous, which means that instead of helping your eye products to stay on longer, they will actually dissolve and melt shadows and liners quickly. Use a light-weight eyelid primer like Benefit Stay Don't Stray ($26) to ensure that shadows stay put.
