The answer the niche question scientists came up with was an anti-UV secretion, which is at first colourless,
then red, then finally brown as the pigment polymerizes.
"The sunscreen property of the sweat was first suspected because albino hippos are often observed - and they seem healthy,"
(Kyoto's Kimiko Hashimoto)
This natural skin-care product not only protects the hippo from the sun, it also regulates temperature and discourages
the growth of bacteria.
Professor Hashimoto and his colleagues collected samples of the hippo's sweat and examined it, to see what makes it so
They found it is made up of two pigments - a red one, called "hipposudoric acid"; and an orange one, called "norhipposudoric
The scientists believe these two substances are produced from a metabolite of amino acids (the building blocks of proteins).
Both pigments act as sun blocks and the red one, they discovered, is a particularly good antibiotic.
At concentrations lower than that found on the hippo's skin, it can inhibit the growth of two types of bacteria. This is
useful for hippos, because they are terrible fighters.
"Hippos are always fighting," said Mr Boardman. "You see them in the wild and they have wounds all over them."
Perhaps it is no wonder, then, that evolution endowed them with a handy antiseptic.
A colleague of Hashimoto added: "They get scratches, bites, and cuts, and yet they don't seem to get infections."
HOW COOL IS THAT