The protein that gives skin and bones much of their strength is collagen.
Collagen is the main structural protein in connective tissues and is especially abundant in skin, bone, cartilage, tendons, and ligaments. Its molecules contain three protein chains wound into a sturdy triple-helix structure. These molecules assemble into fibers that provide high tensile strength, helping tissues resist stretching and tearing.
In bone, collagen forms a flexible organic framework that becomes hardened by mineral crystals, mainly calcium phosphate. This combination matters: collagen helps bone resist pulling and twisting, while minerals provide hardness and compression strength. In skin, collagen fibers support the dermis and work alongside elastin, which helps tissue return to shape.
Collagen is not the same as keratin, the tough protein prominent in hair, nails, and the outermost skin layer. Elastin contributes elasticity rather than being the principal strength-giving framework, while fibrin helps form blood clots. Vitamin C is required for normal collagen production; severe deficiency can weaken connective tissues and cause scurvy.
Humans have many collagen types, but Type I is especially important in skin, tendon, and bone.