Which protein is primarily responsible for the elasticity of the skin?

Elastin is the protein primarily responsible for the elasticity of the skin. This protein allows skin to stretch and then return to its original shape, providing the flexibility and resilience necessary for maintaining a youthful appearance. Elastin fibers form a network in the extracellular matrix of the skin, contributing significantly to its structural integrity and ability to withstand various stresses.

While collagen is another important protein that provides structure, strength, and support to the skin, it primarily contributes to the skin's firmness rather than its elasticity. Keratin, found in hair and nails, serves to protect the skin but does not play a role in its elastic properties. Fibronectin is involved in cell adhesion and helps with wound healing but is not a major contributor to the elasticity of the skin. Therefore, elastin is the key protein that supports the skin's ability to stretch and bounce back, making it the correct answer.