Which type of bonds need to be broken when changing hair from a straight to a curly state?

When changing hair from a straight to a curly state, the primary type of bonds that need to be broken are the disulfide bonds. These bonds are a form of covalent bond specifically found between the amino acids cysteine in the hair's keratin structure. When hair is straightened, these disulfide bonds are restructured. In order to curl the hair, breaking and reforming these bonds is essential, as they largely determine the hair's shape and structure.

Hydrogen bonds, while also influential in the hair's temporary shape and texture, can be altered more easily with moisture and heat. Covalent bonds form the fundamental structure of the hair but are not generally broken during styling processes. Ionic bonds play a lesser role in the structural integrity of hair compared to disulfide bonds and are not the focus when changing the hair’s form from straight to curly. Thus, the breaking and reforming of disulfide bonds is central to achieving the desired curl in hair styling.