An ingrown hair occurs when the distal tip of a hair shaft penetrates and grows back into the interfollicular skin following prior removal via shaving, tweezing, or waxing. The inflammatory response toward the entrapped hair results in the formation of firm perifollicular papules or pustules that can be tender or pruritic.

The condition can affect anyone who engages in hair removal practices, but it is more common in people with tightly curled or coarse hair, which has a higher tendency to curve back toward and penetrate the interfollicular skin. It commonly affects African American men following facial hair removal in the beard distribution, where pseudofolliculitis barbae ensues.