A lip pencil is used to outline and define the shape of the lips before applying lipstick.
It helps prevent the lipstick from bleeding outside the natural lip line, creating a neat and finished look.
By covering the lips with a lip pencil first, the color stays longer and appears more intense.
Foundation is for the face and does not define the lips specifically.
Concealer hides blemishes and dark spots but is not meant to shape lips.
Shadow pencil is used for eyes, not lips.
Therefore, a lip pencil is the correct product to use before applying lipstick.