When a strand of hair is swallowed, the body initiates a physiological process that differs significantly from digesting food. Hair is a complex biological fiber, and its journey through the digestive tract is determined by its unique chemical structure. Most people accidentally ingest small amounts of hair, such as a strand shed while sleeping or one found in prepared food. The ultimate outcome, ranging from harmless excretion to serious medical conditions, depends entirely on the quantity of hair ingested.
What Hair Is Made Of
Hair is primarily composed of a protein called keratin, which makes up about 80% of its weight. Keratin’s physical strength and insolubility come from the numerous disulfide bonds that form cross-links between the protein chains, creating a tough, tightly packed structure.
The human digestive system is not equipped to break down this highly stable protein. Digestive enzymes like pepsin and trypsin cannot cleave the disulfide bonds or penetrate the dense keratin structure. To degrade hair keratin, conditions of extreme acidity or alkalinity, often combined with high temperatures, are required. Since these conditions are not present within the human body, the hair remains fundamentally undigested as it moves through the gastrointestinal tract.
How the Body Handles Accidental Ingestion
When a single, small strand of hair is swallowed accidentally, it passes through the esophagus and into the stomach intact. The hair is smooth and slippery, which means the digestive muscles responsible for moving contents forward, known as peristalsis, struggle to grip and push it.
Despite this difficulty, the hair usually continues its journey through the small and large intestines. The single strand typically becomes entangled within the bulk of other waste material. It then passes harmlessly out of the body during a normal bowel movement. This process usually occurs without any noticeable symptoms or complications, which is why accidental ingestion of a few hairs is not generally a cause for concern.
When Ingested Hair Causes Serious Problems
A different situation arises when a person swallows hair frequently or in large amounts. The hair begins to accumulate in the stomach, forming a dense mass called a trichobezoar, or hairball. These hairballs can grow to substantial sizes, filling the stomach cavity and causing non-specific symptoms, making diagnosis challenging.
Common physical signs include chronic abdominal pain, persistent nausea, and vomiting. Patients may also experience a feeling of fullness after eating, leading to a loss of appetite and unexplained weight loss. In severe cases, the hairball can lead to dangerous complications like gastric ulceration, bleeding, or a complete obstruction of the bowel. Diagnosis is often confirmed using an upper gastrointestinal endoscopy or an abdominal CT scan.
The most extreme form of this condition is known as Rapunzel syndrome, a rare complication where the trichobezoar extends beyond the stomach. A long, tail-like section of the hairball trails from the stomach into the small intestine, sometimes reaching the colon. Treatment for a significant trichobezoar usually involves medical intervention, as the tightly woven mass is too large to pass naturally. Smaller bezoars may be removed via endoscopy, but larger, more solid masses often require surgical removal through a laparotomy or laparoscopy.
The Compulsion to Eat Hair
The chronic ingestion of hair that leads to bezoar formation is almost always linked to trichophagia, the compulsive eating of hair. This behavior is frequently a complication of trichotillomania, defined by the recurrent, irresistible urge to pull out one’s own hair. Estimates suggest that approximately 20% of individuals who pull their hair also engage in eating it.
Trichophagia is classified as a body-focused repetitive disorder, often co-occurring with conditions like anxiety or obsessive-compulsive disorder. The behavior may involve chewing the pulled hair or consuming the entire strand, which increases the risk of medical complications. Treatment involves a coordinated approach, including psychological therapy to address the underlying compulsion and prevent recurrence after a physical bezoar has been removed.