What causes tiny holes in a pot of concealer (make up)?

[quote]
A concealer or colour corrector is a type of cosmetic that is used to mask dark circles, age spots, large pores, and other small blemishes visible on the skin. It is similar to foundation, but thicker and used to hide different pigments by blending the imperfection into the surrounding skin tone. It is normally applied after primer, after foundation and used on the face.

Both concealer and foundation are typically used to make skin appear more uniform in color, and make a clean base for all the other cosmetics. These two types of cosmetics differ in that concealers tend to be more heavily pigmented, though they are available in a wide range of opacity. It also comes in different forms from liquid to solid.
[end quote] ~ Wikipedia

With such a broad description it is impossible to know what you are talking about. I would guess that you are talking about a powder concoction with some small amount of oil to hold it together. That means small air bubbles are pretty much a part of the manufacturing process. Over time the bubbles come out, leaving little holes where they used to be. One trick I happen to know is if the oil dries up you can spray non-stick coating on it and work it in with a teaspoon.