Is hair digestible

Trichobezoar, a hair ball in the proximal gastrointestinal tract, is a rare condition almost exclusively seen in young females. Human hair is resistant to digestion as well as peristalsis due to its smooth surface. Therefore it accumulates between the mucosal folds of the stomach. Over a period of time, continuous ingestion of hair leads to the impaction of hair together with mucus and food, causing the formation of a trichobezoar. [...] In addition, incidentally, parts of the tail can break off and migrate to the small intestine, causing intestinal obstruction [...] When not recognized, the trichobezoar continues to grow in size and weight due to the continued ingestion of hair. This increases the risk of severe complications, such as gastric mucosal erosion, ulceration and even perforation of the stomach or the small intestine. In addition, intussusception, obstructive jaundice, protein-losing enteropathy, pancreatitis and even death have been reported as complications of (unrecognized) trichobezoar in the literature.

-- Gorter RR, Kneepkens CM, Mattens EC, Aronson DC, Heij HA (May 2010). "Management of trichobezoar: case report and literature review". Pediatr. Surg. Int. 26 (5): 457–63