Science, Tech, Math › Science Do Hippos Sweat Blood? Chemical Composition of Hippopotamus Blood Sweat Share Flipboard Email Print Hippos have red perspiration that looks like blood. The pigment protects them from the sun, like natural sunscreen. Marco Pozzi Photographer / Getty Images Science Chemistry Biochemistry Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated May 30, 2019 The hippopotamus or hippo mystified ancient Greeks because it appeared to sweat blood. Although hippos do sweat a red liquid, it isn't blood. The animals secrete a sticky liquid that acts as a sunscreen and topical antibiotic. Color Change Perspiration Initially, hippo perspiration is colorless. As the viscous liquid polymerizes, it changes color to red and eventually brown. Droplets of perspiration resemble drops of blood, although blood would wash away in water, while hippo perspiration sticks to the animal's wet skin. This is because the hippo's "blood sweat" contains a high amount of mucous. Colored Pigments in Hippo Sweat Yoko Saikawa and his research team at Kyoto Pharmaceutical University, Japan, identified non-benzenoid aromatic compounds as the orange and red pigment molecules. These compounds are acidic, conferring protection against infection. The red pigment, called "hipposudoric acid"; and the orange pigment, called "norhipposudoric acid", appear to be amino acid metabolites. Both pigments absorb ultraviolet radiation, while the red pigment also acts as an antibiotic. Reference: Yoko Saikawa, Kimiko Hashimoto, Masaya Nakata, Masato Yoshihara, Kiyoshi Nagai, Motoyasu Ida & Teruyuki Komiya. Pigment chemistry: The red sweat of the hippopotamus. Nature 429, 363 (27 May 2004).