Hippo in the Sun

Hippos live their lives in the sweltering African heat.   They cool off by spending as much as sixteen hours a day in rivers, lakes, streams, etc.  But while this time in the water may be effective against high temperatures, it does nothing to prevent of exposure to UV rays — sunlight which, at that volume, should lead to a lot of hippos with sunburns.  Yet the hippos rarely if burn.  How do they do that?

Easy:  They make their own sun block.

Hippos excrete a orangish-reddish oily sweat which many originally thought to be blood.  It’s not — and it’s not sweat, exactly, either.  It’s a glandular secretion, coming from below the skin’s surface, excreted through the pores.  (Sweat originates from the skin itself.)  The secretion contains particles which help scatter and absorb ultraviolet light, in essence acting as sun block.  And it lasts all day.  The secretion contains two unstable acidic compounds, since named hipposudoric acid and nonhipposudoric acid, which, combined, harden on the hippo and protect the beast, even after hours in the water.  And the substance is incredibly resilient, outlasting the elements: months after scientists had collected it and left it untouched, sealed, on a shelf, it was still free of bacteria, yeast, and fungi.

The implications for human use are being tested, but perhaps one day, we’ll be putting on sun block with SPF H — H, as in hippo.


Bonus fact: Many animals share a feature or two with humans.  Koalas, for example, have fingerprints much like humans, as seen here.

Related: This hippo needs lots of water and sunlight in order to grow.