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Why do snakes and lizards shed their old skin?

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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*).

Snakes and lizards shed their skin—a process known as ecdysis or molting—primarily because their skin does not grow along with their bodies. As these reptiles increase in size, they must periodically replace their outer layer to accommodate their growth and maintain a functional, healthy integument.123

This process serves several vital functions:

Growth: Shedding allows the animal to emerge with a fresh, new layer of skin that fits its current size.13
Health and Hygiene: The process helps remove external parasites, such as mites, that may have attached to the old skin.13
Repair: Because the skin acts as a primary buffer against the environment, it is subject to wear and tear; shedding allows the animal to replace damaged or worn-out outer layers.3

While the physiological goal is the same, the method of shedding differs: snakes typically shed their skin in a single piece, whereas lizards generally shed theirs in patches. This process is hormonally controlled and influenced by factors such as the animal's age, physical condition, and environmental conditions like temperature and humidity.2