Ingrown hair
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Ingrown hair is a condition where the hair curls back or grows sideways into the skin. It may or may not be accompanied by an infection of the hair follicle (folliculitis) or "razor bumps" (Pseudofolliculitis barbae). While ingrown hair most commonly appears in areas where the skin is shaved (beard, legs, pubic region), it can appear anywhere.
Anything which causes the hair to be broken off short with a sharp tip can cause ingrown hair. Shaving is the leading cause, followed by tight clothing. The embedded hair causes a localized inflammation (sometimes painful) response in the skin with prostanoid involvement. Sometimes ingrown hair occurs naturally without shaving.
Symptoms include rash, itching skin, hair which remains in spite of shaving, and infection and pus collecting under skin. Treatments for ingrown hairs include putting a warm washcloth over the ingrown hair, shaving in a different direction, exfoliating with facial scrubs, sponges, towels, or creams containing acids, treatment with Ibuprofen or other NSAIDs, and prophylaxis with twice daily topical application of diluted Glycolic acid. Ingrown hair will often fall out after a couple weeks.