Hippos are known for having unique, heat-sensitive skin – up to about seven times more sensitive than those of other mammals. In fact, they don’t have sweat glands underneath their skin to release excess heat, unlike other mammals. This is why you will often find them spending their days in the water, especially when it is hot, in order to keep their bodies cool and hydrated.
That said, during the cooler seasons of the year you will find them sunbathing alongside the river – to warm themselves up.
While lying in the sun warming up, their skin will start turning very pink, as if they are getting sunburned. Upon closer inspection, it will look like they are sweating blood. This is in fact a red fluid, sometimes referred to as “blood sweat”, discharged from their mucous glands. But it is neither blood nor sweat.
The red, blood-coloured ‘sweat’ acts like a sunscreen, protecting their skin from overheating and dehydration – as their skin becomes very dry once leaving the water and will crack without this natural ‘sunscreen’.
Researchers have now determined that the “blood sweat” is made up of two pigments: red hipposudoric acid and orange norhipposudoric acid. Both of these pigments protect the hippo from sunburn, and the red pigment also has antibacterial properties. These properties are especially helpful after fights, which often leave hippos battered and wounded.
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