From special glands in the skin, hippos secrete a reddish oily fluid, which people sometimes call "blood sweat» by mistake. But, this is not correct. Hippos don't sweat at all. These animals simply do not have sweat glands like humans do.

Instead, these gigantic animals secrete an element containing red pigments known as Hipposudoric acid and an orange pigment known as Norhipposudoric acid. 

Even though the skin of hippos is quite thick, it is very sensitive to both desiccation and sunburn. Therefore, the secretion works for them like a skin salve or sunscreen. It also protects the skin from waterlogging when the hippopotamus is in the water. Hipposudoric acid acts as one of the most effective antibiotics that helps these huge animals protect cuts and other wounds from infection.

Why does the "sweat" turn red?

The protective fluid secreted by the skin of a hippopotamus is transparent. But after a few minutes it turns red. The components of the transparent substance turn into crimson only after coming in contact with oxygen. Therefore, on the skin of an animal, it looks like “bloody sweat”.

Such unusual sweat is essential for a hippopotamus. It is like a powerful sunscreen and an antibiotic cream in one!