What color is a hippo's sweat?
The hippo's skin secretes a natural sunscreen substance which is red-colored. The secretion is sometimes referred to as "blood sweat", but is neither blood nor sweat. This secretion is initially colorless and turns red-orange within minutes, eventually becoming brown. Two distinct pigments have been identified in the secretions, one red (hipposudoric acid) and one orange (norhipposudoric acid). The two pigments are highly acidic compounds. Both pigments inhibit the growth of disease-causing bacteria; as well, the light absorption of both pigments peaks in the ultraviolet range, creating a sunscreen effect. All hippos, even those with different diets, secrete the pigments, so it does not appear that food is the source of the pigments. Instead, the animals may synthesize the pigments from precursors such as the amino acid tyrosine. Nevertheless, this natural sunscreen cannot prevent the animal's skin from cracking if it stays out of water too long.