Hippo sun cream
Stories from Physics for 11-14 14-16
Hippopotamuses secrete a clear fluid that helps to control their body temperature. The fluid turns red-brown within a few minutes of release and gave rise to the myth that the creatures sweat blood. Researchers have found that the fluid blocks both UV and visible light of wavelengths 200-600 nm and so protects the animals from sunburn. The fluid contains red and orange pigments which researchers have labelled hipposudoric and norhipposudoric acid.