What is the component of hair that gives it strength and resilience?

The component of hair that provides strength and resilience is keratin. Keratin is a fibrous protein that makes up the majority of the hair structure. It is highly durable and has a strong molecular structure, contributing to the overall strength of hair. The presence of keratin forms the protective outer layer of the hair shaft, called the cuticle, which helps to prevent damage from environmental factors, styling practices, and chemical treatments.

Other options serve different functions: melanin is responsible for the color of hair, amino acids are the building blocks of proteins including keratin but do not provide structural strength independently, and water plays a crucial role in hydration and health but does not contribute structurally to the hair's strength. Hence, keratin stands out as the key component that imparts the strength and resilience necessary to withstand styling and environmental stressors.