PSI Barbering Practice Exam 2026 - Free Barbering Practice Questions and Study Guide

The type of bond described as weak and easily broken by water or heat is the hydrogen bond. These bonds form when a hydrogen atom, which is covalently bonded to an electronegative atom, is attracted to another electronegative atom nearby. This makes hydrogen bonds relatively weak compared to covalent or ionic bonds.

In the context of hair, hydrogen bonds play a significant role in the hair's texture and shape. They are responsible for temporary changes in hair structure, such as when wet hair can be reshaped and re-styled. Because hydrogen bonds can be easily disrupted by moisture or heat, hair can revert to its original shape once these conditions change, illustrating the transient nature of these bonds.

Disulfide bonds, on the other hand, are strong covalent bonds that involve sulfur. They are much more stable and are not easily broken by water or heat alone. Sulfide bonds are generally not referred to in the context of hair or biological molecules. Salt bonds, while also important in hair structure, are ionic interactions that are stronger than hydrogen bonds and are typically influenced by pH and ionic strength rather than thermal or hydrous environments. Thus, the focus on the weak and easily disrupted characteristic specifically points to hydrogen bonds.