Hippo sunscreen, no sweat
Want to be hip at the beach while being cool and healthy too? Try Hippopotamus sweat.
Not only is the sweat of the hippo a fetching shade of red that gradually turns to brown, it acts as a sunscreen and has antibiotic properties, according to Japanese scientists writing in the journal Nature.
But before heading off to the zoo for sweat samples, a word of caution.
The scientists at Keio University in Yokohama say there is a downside. It stinks.
The researchers collected sweat samples from the face and back of a hippo at Ueno Zoological Gardens in Tokyo.
Strictly speaking, the viscous fluid that hippos produce isn't really sweat, as it is secreted from different glands to sweat. But it acts like sweat as it helps hippos to control their body temperature.
The researchers analysed the fluid's content using a range of techniques including x-ray crystallography, mass spectroscopy and nuclear magnetic resonance imaging.
They found unstable red and orange pigments that turned out to be aromatic compounds, naming the red one hipposudoric acid and the orange one norhipposudoric acid.
The researchers then set out to find out what these pigments did.
As the pigments absorbed light in the 200 to 600 nanometre range of the spectrum, the researchers concluded they acted as sunscreen pigments.
They also found that the red pigment acted like an antibiotic.
At concentrations lower than would normally be found on hippo skin, the pigment inhibited growth of the disease-causing bacteria Pseudomonas aeruginosa and Klebsiella pneumoniae.
While the isolated pigments were unstable in the laboratory, the researchers said they were more stable on hippo skin when they dried in the presence of mucus.
This meant that in the wild, the pigments kept their colour for several hours before polymerising into brown solids.