What do you think of this fact?
If you see a hippo up close, you might notice a reddish film on its skin. People used to say hippos sweat blood. The truth is better.
Neither blood nor real sweat
According to Nature, the secretion is “neither blood nor precisely sweat”. Hippo biologist Keith Eltringham of Cambridge told Science News that hippos lack the glands that produce true sweat. What comes out of their skin is a mixture all of its own.
The fun part is how it changes. According to Science News, the fluid starts out colorless. Within minutes it turns red-orange, and later it slowly goes brown.
Two pigments, two jobs
In 2004, a team led by Kimiko Hashimoto of Kyoto Pharmaceutical University took a closer look. The samples came from two hippos at Ueno Zoo in Tokyo, Satsuki and Jiro. Their keepers wiped the animals’ skin with gauze to collect them.
In the lab, the researchers found two pigments: a red one called hipposudoric acid and an orange one called norhipposudoric acid. Both absorb light most strongly in the ultraviolet range, which works like built-in sun protection. Photobiologist Gavin Greenoak told Science News: “There’s no question that the hippo is getting its sunscreen.”
The red pigment can do even more. According to Nature, it slowed the growth of two disease-causing bacteria in the lab, so the mixture may also work as a natural antibiotic. Science News links this to the fact that hippo wounds rarely get infected, despite their fierce fights.
Bonus fact: According to Nature, adult hippos can stay underwater for more than five minutes.
An idea for humans?
Hashimoto thought more stable versions of the pigments could one day become interesting for medicine. The catch: on their own, the compounds aren’t stable. In the complete secretion they keep their color for several hours, probably because mucus protects them.
So the dangerous-looking hippo walks around in sunscreen with wound protection built in, and it makes the stuff itself.