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Scientists Uncover Secret of Hippo Sunscreen
June 2004
Hippopotamuses' slimy sweat gradually turns red on their skin, leading to the myth that hippos sweat blood. These bulky creatures spend their days in or near the rivers, lakes and wetlands of sub-Saharan Africa, grazing nearby grasslands at night.
But mere smatterings of fine hairs cover a hippo's body, leaving the skin exposed. Scientists have long speculated about the helpful properties of their colorful perspiration, and a recent study completed by researchers in Japan finally provides some definite answers.
The substance isn't actually sweat—hippos have special subdermal glands rather than sweat glands—but it does help to regulate body temperature. After swabbing a hippo's slick face and back with gauze and isolating specific chemicals from the slime, the research team found both a red and an orange pigment. They named these pigments hipposudoric acid and norhipposudoric acid, respectively.
The pigments absorb light in the UV range suggesting that the hippos' ruddy sheen shields them from the sun's rays. The research team also discovered that the red pigment inhibits the growth of certain pathogenic bacteria at concentrations lower than those found on the hippos skin. The secret of the hippos' blood-red secretions is out; they make their own brand of antibiotic sunscreen.
Source: May 27, 2004, Nature
