Concealers are of a thicker composition than regular foundations and are usually available in the form of sticks, tubes, pots, and creams.
Concealers are used to cover imperfections such as:
Dark circles under the eyes
You want to choose a shade of concealer that matches your skin tone as closely as possible. Using a concealer that is much lighter than your skin will actually emphasize rather than cover any blemishes you may have and can make puffy eyes appear even puffier because light colors stand out and darker colors recede.