Hair is composed of which protein?

• A. Keratin
• B. Collagen
• C. Melanin
• D. Elastin

Answer: (A)

Hair is made primarily of the structural protein keratin. Keratin is a tough, fibrous protein that forms the long filaments in hair, nails, and the outer layer of skin. In hair, these keratin filaments align into strong bundles, giving the hair its strength and rigidity. The high cysteine content of keratin creates many disulfide bonds between chains, which contribute to hair’s curl, stiffness, and its ability to resist stretching. This is also why chemical treatments that break or reform those bonds—like bleaching or perms—change hair’s texture. Collagen is a connective-tissue protein, not the main hair component; melanin is the pigment that gives hair its color; elastin provides elasticity in some tissues but isn’t the primary hair protein.