Hippos Produce Their Own Sunscreen

By Kevin Ritchart

Because they are widely considered to be among the most violent and aggressive animals in the world, studying the hippopotamus — particularly in its natural habitat — is a challenge for scientists. For years, researchers have been curious about both the source of the reddish substance that appears on the skin of the hippo, and through testing it’s now known what purpose it serves.

Despite the difficulty of getting close to these massive creatures in the wild, a Japanese team of scientists was able to collect samples of the hippo’s secretions and subsequently test them to determine their makeup. The scientists separated the chemical compounds from the hippo’s sweat using water and found them to be two highly unstable and highly acidic compounds. One was red in color and dubbed hipposudoric acid. The other had an orange tint and was named norhipposudoric acid.

Built-in Protection

Despite being unstable on their own, when the two compounds combine in the presence of mucus and then dry on the hippo’s skin, the resulting substance remains in place for hours at a time to protect the hippo from the sun. Further testing of the compounds revealed that hipposudoric acid also contains antibiotic properties. Even in low concentrations, the highly acidic compound — which is hundreds of times more powerful than vinegar — has shown the ability to control the growth of pathogenic bacteria.

This helps to explain why hippos remain largely free of infection despite the fact that they can inflict deep wounds with their ivory tusks, which can grow as long as 20 inches. Before they battle over potential mates by butting heads or violently gashing each other with their tusks, hippos engage in a ritual called gaping in which they stand face to face and open their mouths to show their teeth. If the sight of the other’s tusks doesn’t cause one hippo to back down, a fight ensues.

Hippos are considered semiaquatic animals, as they spend up to 16 hours every day submerged in water and only venture onto land after nightfall to hunt for food. Staying in the water is effective at keeping the animals cool during the day, but it doesn’t protect their skin from the sun’s rays.

While some research has been conducted, there’s still a great deal that’s unknown about the hippo’s so-called built-in sunscreen. Scientists believe that the substances are synthesized from amino acids upon exposure to oxygen.