The African bush elephants' wrinkled skin is one of its most defining characteristics. Scientists know that the wrinkles help elephants stay cool. That's because the wrinkles trap moisture. There was something they did not know, however. How does their skin get wrinkly?

A new study offers a surprising explanation for elephants' wrinkly skin. The mammals' skin thickens over time. New layers of skin place pressure on the outermost layer of skin. This outer layer is called the stratum corneum. This pressure makes the skin wrinkle.

At first, scientists thought that elephant skin wrinkled like dried mud or damaged concrete. The new study's co-author is Michel Milinkovitch. He works at the University of Geneva and studies animals' bodies and how they change. In a 2013 study, Milinkovitch found that shrinking skin made the scaly folds seen on crocodiles' skin.

Comparing Elephants To Crocodiles

Milinkovitch and his coworkers took close-up looks at elephant skin samples. They created a computer model that simulated skin growth in order to see similarities between crocodiles and elephants. The team expected to see the skin shrink. The layers actually appeared to bend.

Milinkovitch said it seems odd that wrinkly skin would be helpful.

The scientists' findings make sense, though. Elephants lack the sweat and sebum glands that most mammals rely on to keep cool. For example, humans sweat when we get hot. Instead, elephants must splash around in a pool of water or mud. Thanks to their cracked skin, they end up keeping five to 10 times more moisture than a smooth skin surface. As this liquid evaporates, it helps elephants to cool their body temperature. It helps prevent dehydration, or losing too much water.

The cracking seen in elephant skin is usually seen in non-living things. The elephant's skin cracks because of skin layers bending. Most living things that have cracked appearances get it because their tissues get folded up.

Elephants' unusual skin actually has a lot in common with humans who have a skin disease called ichthyosis vulgaris. This condition affects 1 out of every 250 people. The disease prevents the shedding of dead skin cells. The shedding of dead skin cells helps our skin stay smooth. The disease has no cure but is often treated with moisturizers. The disease makes the skin dry, thick and scaly.

This is a problem for humans, but it's great for African elephants. As skin cells pile up, they bend the outer layer. These cracks help them to stay cool.

Milinkovitch said that shedding skin makes the skin smooth again. If the elephants shed their skin, the skin would not get thick and they would not get the wrinkles. "In humans, this is not a helpful problem," he said.

Scientists Will Study Baby Elephants

Scientists must keep looking for a link between elephant skin and ichthyosis vulgaris. A link would be an example of how a harmful human change is great for other animals, experts said. This study might help scientists find a cure for humans with the disease.

Milinkovitch's next step will be to watch the growth of a newborn African elephant.

"We would like to follow the cracking on the skin of a baby African elephant to understand the dynamic of the process," he said. He has many questions about how the cracks start forming. "It's a new, beautiful example of how physical processes are involved in the development of animal forms and shapes."