A hair tourniquet (HT) occurs when a piece of hair becomes wrapped circumferentially around an appendage or other body part, impairing venous drainage or lymphatic flow, resulting in pain, swelling, or ischemia of the appendage. HTs are uncommon and seen primarily in neonates / infants, most often involving the toes or fingers but sometimes involving the genitalia. They are rarely seen in older children and adults, and when found, may be intentional. Unintentional HTs of the labia or clitoris have been reported in postpubertal females. Most HTs involve head hair from the birth parent that is likely shedding at high rates due to postpartum telogen effluvium.

Once a piece of hair becomes wrapped circumferentially around an infant's appendage, if the affected appendage is covered, such as toes in socks or footed pajamas, fingers in hand mitts, or a penis in a diaper, movement of the appendage may cause further entanglement and tightening, creating a tourniquet.

Infants often present with nonspecific irritability or crying, and the HT is only found on careful inspection of all digits and genitalia. Sometimes a caregiver will note a swollen, red appendage or cut-like constriction of the skin on the affected appendage. Severe HTs can result in infection of the appendage or even amputation. Rarely, HTs are intentional and represent child abuse.