Though as bare-skinned as humans, hippos avoid burning up in the hot equatorial sun. Now researchers have demonstrated that hippos beat the heat by sweating out their own brand of sunscreen.
In the study, scientists led by Yoko Saikawa of Keio University in Yokohama, Japan, swabbed the sticky secretion off the backs of captive hippos. When first exuded, the fluid is clear but soon polymerizes into a reddish-brown molecular chains. In the lab, the researchers identified red and orange pigments in the slime.
The red pigment, dubbed hipposudoric acid, absorbs light in the visible and ultraviolet spectrum, suggesting it can function as sunblock. The slime also appears to serve as an antibiotic ointment. When the scientists added the slime to colonies of disease-causing bacteria from hippo skin, even low doses of the slime stopped the bacteria from proliferating. The research was reported in the journal Nature.