[george (OP)]

How does a perm work? What does it do to the hair to make it curly, and why do some people have an "auto-perm" i.e. naturally curly hair?

George

[rosy]

I'm not sure why some people's hair is curly, but I believe a perm is created by exploiting the chemistry of the hair itself:
Hair is made of a type of protein which is held together partly by disulphide bonds- bonds between two atoms of sulphur either within the protein or between neigbouring protein molecules. Applying a reducing agent to the hair breaks these bonds (takes disulphide -S-S- to two seperate thiols -SH HS- ) making the hair much less stiff. The hair is then formed into the desired styl and reoxidised so that new disulphide bonds form in the new position.

Does that help?

[gecko]

the elementary answer as to why hair is curly or straight: straight hairs are round, and therfore stay straight, like a cylinder, while curly hairs are flat, and curl like a ribbon.

but i dont know how a perm works.