Ingrown hair is a condition where hair curls back or grows sideways into the skin. Ingrown hair is commonly caused by shaving, waxing or tight clothing. When the hair grows inside the follicles underneath the skin, it generates foreign body reaction in the hair follicle causing an infection. The inflammation of the follicle then produces an unattractive bump, rash, itchy skin, and pus collecting under the skin. Ingrown hairs are most common on the face, legs, arms, pubic region, head, neck, and other shaved areas.