Ask A Scientist Chemistry Archive

Question:  What makes curly hair curly?
 john h hersey
 
Answer:
Hair is made of protein (just like pretty much everything else in
your body).  Now in these proteins are sulfur atoms (called sulfides).
When two sulfur atoms come together, they form what's called a
disulfide bond.  If two sulfur atoms are far apart in the same protein,
and they come together to form that bond, the protein is going to bend
accordingly.  The more disulfide bonds, the curlier the hair.  Naturally
curly hair has a lot of disulfide bonds.  When people with straight hair
get a 'perm' they are chemically forcing the making of disulfide bonds.
These bonds are pretty strong too...very difficult to break.  'Perm' is
short for 'permanent wave' though a 'perm' isn't really permanent.  As the 
new hair grows in, it will be straight and only the ends curly.  And it's 
very difficult to straighten out naturally curly hair.
-Joe Schultz