Hair tourniquet is a condition where hair or thread becomes tightly wrapped around most commonly a toe, and occasionally a finger, genitals, or other body parts. This results in pain and swelling of the affected part. Complications can include tissue death due to lack of blood flow. It occurs most commonly among children around 4 months of age, though cases have been described in older children and adults.

Most cases occur accidentally. Risk factors may include autism and trichotillomania. The mechanism is believed to involve wet hair become wrapped around a body part and then tightening as it dries. Diagnosis involves examination of the entire child. Prevention is by keeping the parent's hair from contact with the baby such as by the parent keeping their hair brushed and back and washing the baby's clothing separately.

Treatment is with a substance that breaks down hair or cutting through the hair. The condition is rare. Males and females are equally frequently affected. The first medical description dates from 1832. In some cultures thread is tied around the penis of children with bedwetting or for luck.