The first known procedures to bend straight hair into curls dates from 3000 B.C.: Hot Curlers made from clay were used. The hair was apparently dry. What kind of bonds was/were actually broken and reformed?

Question

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Hydrogen bonds are responsible for the temporary bonding in hair that allows it to be curled or straightened using heat. When hair is exposed to heat, the hydrogen bonds break, allowing the hair to be reshaped into curls or straightened, and then they reform as the hair cools. This process is often referred to as "thermal reconditioning" or "thermal styling." ionic bonds are stronger and are bonds between opposite charges, whereas disulfide bridges are even stronger bonds formed by covalent bonding between two sulfhydryl groups on cysteine amino acids in the hair protein structure. Dipolar bonds are not a type of bond that exists in hair.

The First Known Procedures to Bend Straight Hair into Curls