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How does reptile skin reduce water loss on land?

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A pangolin walks through grass with a blue circle around it and the word endangered written in white across the image. — Integument The pangolin is the only mammal in the world covered in scales.

Reptiles are the first truly terrestrial vertebrates, and their ability to thrive on land is largely due to their specialized integument. To prevent desiccation—the loss of body water to the environment—reptiles possess a thick stratum corneum. Within this layer, waxes are arranged in membrane-like structures between keratinized cells, creating an effective barrier against water loss.1

This protective layer is further strengthened by beta keratin, a stiff material that provides structural integrity to the epidermis. While the specific arrangement of these keratin layers varies among groups—such as between the overlapping scales of lizards and snakes versus the scutes of crocodiles and turtles—the presence of these cornified surfaces is essential for maintaining internal water balance in terrestrial habitats.1