Do hippos really sweat blood?
When you head to a beach to spend a day under the hot sun, there’s one thing that you are asked to use without fail. Yes, we are talking about a good sunscreen that will help protect your skin from those strong UV rays. Ever wondered what animals do? Well, some of them have thick fur to protect their skin. The hippopotamus, or as it is famously called, the river horse, sweats blood to protect itself. Yes, you read it right!
The really clever thing about hippos is that they can avoid getting sunburn by producing their own sunscreen, in the form of a sticky reddish sweat often called ‘blood sweat’. How interesting! Let’s find out more.
Sweating blood: Is it really ‘blood’ and ‘sweat’?
Hippos secrete this reddish oily fluid from special glands in their skin. But the fluid is not sweat. Unlike sweat, which some mammals (including humans) secrete onto their skin, where it evaporates and therefore cools the body, this fluid functions as a sunscreen, skin moisturiser, water repellent and antibiotic. It appears red when exposed to full sunlight, which led the first European discoverers in Africa to call it "blood sweat."
The evolution and the science
Hippos consume as much vegetation as they can during the night when they are shielded from the searing heat and sun. At dawn, they retire to the water and spend their days resting, squabbling and, most importantly, digesting. Because it is so important for hippos to eat a huge amount, they must venture out in the sun from time to time, to top up on their nightly binge. So, a traditional sunscreen - like fur - is not practical if you spend half your time submerged in water. The answer that evolution came up with was an anti-UV secretion, which is at first colourless, then red, then finally brown as the pigment polymerises.
Their skin is very sensitive to both drying and sunburn, so the secretion acts like an automatic skin ointment. It also protects the skin from becoming waterlogged when a hippo is in the water. It also acts like sweat in helping to control body temperature.
You would be surprised to know that the detailed chemical composition of this thick red liquid oozing from its pores, which is unique to hippos, remains something of a mystery even today. What scientists have been able to conclude is that the fluid is produced by hippos’ subdermal glands and is made up of two unstable pigments - one red, the other orange. These two substances are produced from a metabolite of amino acids (the building blocks of proteins). Both pigments act as sun blocks and the red one, they discovered, is a particularly good antibiotic that works to protect the hippo from certain pathogens and accelerate its recovery from wounds. This of course comes in handy for hippos since let us tell you that they are terrible fighters and have wounds all over them after their frequent fights with each other. And yet, you see them not catching infections!
Lazy, dangerous and bad swimmers
They are known as one of the laziest animals as they sleep all day but this docile-looking animal could also be very aggressive. Hippos can sleep underwater, using a reflex that allows them to bob up, take a breath, and sink back down without waking up. Yet despite all these adaptations for life in the water, hippos can't swim — they can't even float!
Getting to the list of endangered species
Hippos could be added to the list of the world's most endangered animals because of their dwindling population, thanks to climate crisis, poaching and the ivory trade. The semi-aquatic mammals are found in lakes and rivers across sub-Saharan Africa, with a current estimated population of 115,000-130,000.