What is an essential characteristic of human hair?

Elasticity is a fundamental characteristic of human hair. This property refers to the hair's ability to stretch and return to its original length without breaking. The elasticity of hair is crucial because it helps maintain the integrity and durability of hair during various styling processes, such as brushing, curling, or straightening. Hair with good elasticity can withstand manipulation and stress without sustaining damage, making it essential for healthy hair maintenance and styling.

The options that describe hair as colorless, waterproof, or unbreakable do not accurately reflect human hair characteristics. While hair can come in various colors and may have some degree of water resistance, it is not completely waterproof. Additionally, no hair is truly unbreakable; all hair has a breaking point under extreme stress or damage. Hence, elasticity stands out as the most critical and accurate characteristic among the choices provided.