"Certain foundations work better with a sponge or brush," Alex says, "but definitely use either one or the other — never your fingers. The less you can touch your face, the better." (Bacteria, dirt, etc., can be left behind.) Your fingers can also leave behind fingerprints, "so the look isn't as smooth and finished-looking." If you use a sponge, apply foundation by stippling the sponge, not swiping it across the skin. This gives your foundation a more natural look, and blends it more evenly into the skin.