"Pseudofolliculitis" (PFB) or "ingrown hairs" (IH) or "razor bumps" (RB) are the same condition. Hairs normally grow straight out of a tube in the center of a hair follicle. "STRAIGHT" hairs have a circular cross-section (o). "CURLY" hairs have an oval cross-section (0), and tend to fold or curve like a tulip’s leaf.

An "ingrown hair" is a shortened hair that does not grow straight out of the follicle opening. Instead, it curls into the side wall of the hair follicle. This penetration into and through the wall of the hair follicle produces an inflammation, which can result in the development of a pimple (such as a papule or a pustule) or a cyst (nodule). These lesions are usually tender.

As the hair continues to grow above the opening of the follicle, it can pull the hair tip out of, or keep the hair tip from growing into the side of the follicle. Alternatively, the hair tip may continue to grow into the adjacent skin outside of the follicle and produce a large and probably more inflamed area. This inflammation can produce permanent SCARRING and/or color changes of the skin (such as darkening [hyperpigmentation] and/or lightening [hypopigmentation]).