Missouri Board of Cosmetology Practice Exam

Which type of bond is affected when relaxing hair?

1. Ionic bonds

2. Hydrogen bonds

3. Disulfide bonds

4. Salt bonds

The correct answer is: Disulfide bonds

When relaxing hair, the type of bond that is significantly altered is the disulfide bond. Disulfide bonds are strong chemical links formed between the sulfur atoms of cysteine amino acids in the hair's protein structure (keratin). These bonds play a crucial role in the hair's strength, shape, and overall structure. Relaxing treatments typically involve the application of a chemical that breaks the disulfide bonds, allowing the hair to be reshaped. This process is essential for straightening curly or wavy hair. Once the disulfide bonds are broken, the hair can be molded into a new form. After the treatment, the bonds may re-form in the new shape as the hair dries or when a neutralizing agent is applied. The other types of bonds mentioned, such as ionic bonds, hydrogen bonds, and salt bonds, interact differently within the hair structure. While they do play roles in hair's overall properties, they are not the primary focus in the hair relaxing process. Hydrogen bonds, for example, are weaker and typically affected by moisture and heat, and they reform quickly once the hair returns to its original state. Hence, they do not provide the lasting change associated with hair relaxing treatments. Understanding the role of disulfide bonds