The Incredible Reason Hippos Have Red Sweat

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Besides elephants and rhinoceroses, hippopotamuses are the largest living land animal. Though they resemble giant pigs, their closest relatives are cetaceans like whales and porpoises. Hippos are characterized by large, barrel-shaped torsos, stocky legs, and large mouths containing equally large canine tusks.

They are huge and stocky, but despite this frame, can run upwards of 20 miles per hour for short distances. Due to their unpredictable, and often aggressive behavior, they are considered one of the most dangerous animals on earth. Their appearance isn’t their only unique characteristic, however. Hippos emit a blood-like substance that looks like sweat. What is this peculiar secretion? Watch the video above, and then we will explore the topic further.

Red Sweat

Let’s say it’s a particularly hot day on the Kalahari. The native hippopotamuses spent most of their time in bodies of water, cooling off in the mud and periodically coming to land. The sun is bright, however, and hippos have almost no hair on their bodies. Their skin is thick, nearly two and a half inches thick, but does not provide much protection from the sun.

To combat this problem, hippos have developed a remarkable function: red sweat. In certain moments, hippos will secrete a substance across the surface of their bodies. Initially, it’s colorless. Within minutes, however, this secretion turns red and eventually, brown. To the untrained eye, it would appear to be blood. Instead, it’s a vital function of the hippo’s physiology.

Sweat … or Something Like It

That blood-like secretion that appears on hippopotamus skin is neither sweat nor blood. It’s actually a mixture of antibacterial lotion and sunscreen. Scientists have identified the “red sweat” as containing two highly acidic pigments: red hipposudoric acid and orange norhipposudoric acid. The red sweat inhibits the growth of disease-causing bacteria. Furthermore, the light absorption properties of this secretion sit in the ultraviolet range, producing a sunscreen-like effect.

All hippos, including pygmy hippos, produce this secretion. It doesn’t matter what they eat, their bodies produce this “red sweat.” When isolated, these two pigments are highly unstable. When combined, however, they have impressive antibiotic and sun-protection properties. Despite these benefits, it only works for so long. If a hippo stays out of the water for too long, its skin will begin to crack, regardless of the presence of its blood sweat.

Mysteries Remain

When European explorers first witnessed this unique property of hippos, they thought it to be blood. In the ensuing centuries, science has developed a deeper understanding of this natural moisturizer but questions remain. While scientists have isolated the chemicals responsible for the secretion, the jury is still out regarding its origins. Some experts believe it’s synthesized out of amino acids within the hippos like tyrosine.