The human body cannot digest hair. Hair is not a source of nutrition because the digestive system is incapable of breaking it down. This indigestibility results from the hair’s unique, highly durable structural composition. Hair is fundamentally a protein structure, but the specific type of protein is resistant to the processes that routinely digest protein in food.
Keratin: The Indigestible Building Block
Hair is composed almost entirely of a tough, fibrous structural protein known as keratin. This protein differs significantly from the globular proteins found in meat or dairy, which the body easily dismantles. Hair’s resistance to digestion stems from the highly organized structure of keratin, which involves many cross-linked chemical bonds.
Keratin molecules are bound together by numerous disulfide bonds, creating a rigid, cable-like structure that is insoluble and strong. Digestive enzymes, such as pepsin in the stomach and trypsin in the small intestine, are proteases designed to break the peptide bonds of typical proteins. However, they lack the specific enzymatic machinery, called keratinases, required to cleave the numerous disulfide bridges in hair keratin.
The highly acidic environment of the stomach, while powerful, is not sufficient to dismantle this keratin structure. Only specialized organisms, such as certain fungi and bacteria, produce keratinase enzymes capable of degrading hair. Since humans do not produce these enzymes, the hair remains chemically intact throughout the entire digestive process.
The Journey of Swallowed Hair
When a small strand of hair is accidentally swallowed, it begins an uneventful passage through the gastrointestinal tract. Since the hair cannot be chemically broken down, it moves through the system unchanged. Its smooth and flexible physical properties allow it to be pushed along by the muscular contractions of the esophagus and intestines, a process called peristalsis.
The strand travels from the stomach into the small intestine and then the large intestine without being absorbed. The hair is incorporated into the mass of undigested food and waste material. It is then safely expelled from the body during a normal bowel movement, presenting no health risk.
When Ingested Hair Causes Problems
While small amounts of hair pass safely, the compulsive eating of hair, a disorder known as trichophagia, can lead to serious medical complications. Repeated ingestion causes the strands to accumulate and tangle within the stomach. This mass of compacted hair is called a trichobezoar, which can grow large over time.
As the trichobezoar increases in size, it can block the passage of food and fluid, leading to symptoms like abdominal pain, nausea, vomiting, and weight loss. The mass can also cause severe complications, including bowel obstruction or, in rare cases, perforation of the stomach or intestinal wall. The hairball’s surface, often coated in mucus, can prevent it from passing naturally through the pylorus, the exit of the stomach.
The most severe manifestation of this condition is known as Rapunzel syndrome, a rare form of trichobezoar. This occurs when the hair mass forms a long tail that extends past the stomach and into the small intestine. Due to its size and location, surgical intervention is often required for removal, highlighting the dangers of retained, undigested hair.