Pressure-induced alopecia (PIA) refers to hair loss induced by localized pressure on the scalp due to prolonged immobilization. It is thought to arise from localized tissue hypoxia leading to cessation of hair follicle activity. This results in a focal area of hair loss occurring several days to weeks after the initial trigger. The alopecia may be nonscarring (if diagnosed early) or scarring (if diagnosis is delayed). Any age group may be affected, including neonates and children.

Predisposing factors associated with PIA include postoperative stays, prolonged hospital stays, orthodontic headgear, surgical head and neck positioners, cervical collars, electroencephalogram monitoring, and recreational activity associated with a fixed posture. Other associations include long durations of immobilization, obesity, female sex, psychiatric or cardiovascular comorbidities, use of the Trendelenburg position, and intraoperative hypoperfusion / hypoxemia.