Final answer:
When hair gets wet, hydrogen bonds are disrupted, allowing temporary changes in its shape as it dries. The more robust disulfide bonds in hair's keratin require stronger treatments to break, leading to permanent alterations.
Step-by-step explanation:
The bonds that are broken when hair is wet and then dried are primarily the hydrogen bonds. When water molecules enter the hair strands as they get wet, they disrupt the hydrogen bonds that help maintain the alpha-helices in the hair's proteins. As the hair dries, these hydrogen bonds can reform, which allows temporary changes in hair shape, such as straightening or curling.
However, the disulfide bonds, which are strong covalent bonds between sulfur atoms within the hair's keratin, are not broken by water. They require harsher treatments, such as those involved in permanent waving or straightening techniques, where reducing agents are applied to break these bonds, allowing a more long-term change in hair structure.