Apparently the ingredients label on a loaf of bread that includes an ingredient called L-cysteine may in fact be an ingredient made from human hair. I read that some L-cysteine is directly synthesized in laboratories, most of it is extracted from human hair, a cheap and abundant natural protein source. The hair is dissolved in acid and L-cysteine is isolated through a chemical process, then packaged and shipped off to commercial bread producers. L-cysteine is usually not added directly to flour intended for our home use, but you can find it used throughout commercial breads ie bread rolls, pizza dough and pastries.
The article I read said that besides human hair, other sources of L-cysteine include chicken feathers, duck feathers, cow horns and petroleum byproducts. Most of the hair used to make L-cysteine is gathered from the floors of barbershops and hair salons in China, by the way. Yummy!