Hippos Sweat Sunscreen ? And It Looks Like Blood

If you ever spotted a hippo on a hot day and noticed an alarming red-pink sheen coating its skin, don't panic ? it's not bleeding. It's doing something far more impressive: manufacturing its own industrial-strength sunscreen directly from its pores.

The liquid hippos secrete is nicknamed "blood sweat" ? a label that's exactly two-thirds wrong. It isn't blood, and it isn't sweat. Scientists discovered it's a unique skin secretion containing two pigments: one red (hipposudoric acid) and one orange (norhinosudoric acid). Together they absorb UV radiation and keep the hippo from turning into a very large, very miserable sunburn.

There's a bonus, too. This same liquid has antibiotic properties, helping hippos fend off infections from the rather enthusiastic territorial battles they're known to have. A hippo, essentially, comes pre-loaded with its own first-aid kit built right into its skin.

Ancient observers, sensibly alarmed by the sight of a two-ton animal oozing something red, concluded the obvious: hippos must sweat blood. An understandable mistake. It's just that the truth turned out to be considerably weirder.