How does a permanent wave change the shape of hair?
Keratin contains S-S bridges that help stabilize each hair fiber. Thioglycolates reduce some of these disulfide bonds to thiols, opening molecular cross-links.
The hair is held in a new shape, then an oxidizing treatment helps form disulfide bonds again and stabilize the rearranged structure.
The chemistry of a perm is surprisingly simple:
open molecular bridges -> reshape the material -> rebuild the bridges.
Global Chemical Database