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What role does keratin play in reptile scales?

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A painted turtle (Chrysemys picta) with a dark shell and red and yellow markings rests on a rock near water, surrounded by green aquatic plants. — reptile Painted turtle (*Chrysemys picta*).

In reptiles, keratin is a vital structural protein that strengthens the epidermis and forms the primary material of their scales.12

Reptilian scales are composed of two types of keratin, which provide a balance between protection and flexibility:

Beta-keratin: This is a stiff, rigid material that provides structural strength and durability to the outer surface of the scales. In many species, such as crocodiles and turtles, the outer scale surface consists exclusively of beta-keratin.1
Alpha-keratin: This is a more pliable, flexible protein. It is often found in the "hinge" regions between scales, allowing the animal to move freely.1

In lizards and snakes, these two types of keratin work together in continuous layers, with the alpha-keratin located beneath the tougher beta-keratin. By forming this cornified, keratinized layer, reptiles are able to prevent desiccation, effectively solving the challenge of water loss in terrestrial environments. The stability of these proteins is further enhanced by disulfide bonds, making the scales highly resistant to environmental degradation.12