Re: Why can't humans digest hair?

Digestion of hair.

Hair is composed of proteins [keratins] which have a very highly ordered 
structure. They have a fibrous character due to their very specific 
ordering of these proteins forming the cable like structure of hair. Only 
under very specific conditions such structures can be altered. During a 
hair treatment to induce curling, the proteins are chemically altered using 
reducing agents to restructure the proteins but they are not degraded. In 
order to degrade the hair proteins it is essential to treat them at very 
acid or alkaline conditions at high temperatures well bove 100C during very 
long times. Such conditions do not exist in the digestion system of humans. 
Although the pH is sufficiently low and the enzymes [other proteins] of the 
stomach are able to digest=hydrolyse to other proteins, these conditions 
are still too mild for the hydrolysis of hair and they leave the body 
undigested.