How large can blackheads get?

Blackheads are typically the size of the pores or hair follicles they clog, between 2 and 4 millimeters, according to AskAnEsthetician. However, blackheads can grow larger. In 2013, a woman had one removed after 25 years that had grown to about the size of an eraser head, reports Jezebel.

Blackheads are not always black; some are more yellow in color, notes Medical News Today. They consist not of dirt, but of skin cells and sebum, or oil, that gather in a person's hair follicles. Their main cause is the overproduction of oil. Blackheads most commonly appear on the nose and face and can develop into pimples.