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Secretion protects skin: hippopotamus


Hippopotamus-1 / Patrick Gijs.. / LicenseCC-by-sa - Attribution Share Alike

A secretion of the hippopotamus protects its skin from the sun and bacteria thanks to two pigments that absorb UV light and have antibiotic properties.

"The rust-colored perspiration of the hippopotamus does more than keep the animal cool. Hippo sweat contains pigments that act as both sunscreen and antibiotic. Researchers at Kyoto Pharmaceutical University in Japan identified two such pigments, the red hipposudoric acid, and the orange norhipposudoric acid. Both are conjugated three-ring structures. The two compounds absorb light in the UV-visible range (200-600 nm) and so are thought to protect the hippo's dermis from the sun. Additionally, low concentrations of hipposudoric acid inhibit the growth of bacteria. Both compounds are highly reactive, and tend to polymerize when removed from the hippo and/or a water source. An unknown agent in hippo mucus keeps the compounds from polymerizing for several hours, even after the hippo sweat dries." (Courtesy of the Biomimicry Guild)

"The efficient sunscreen activity of NH and HP stems from their broad absorption in the UVA and UVB regions of the spectrum." (Galasso and Pichierri 2009:2543)

"Although the fluid secreted by the hippopotamus (Hippopotamus amphibius) is not strictly sweat as it is produced by the subdermal glands, it acts like sweat in helping to control body temperature. It is also thought to be antiseptic…What is the function of these pigments as far as the hippopotamus is concerned? Their spectra in the ultraviolet/visible range (200–600 nm; see supplementary information) indicate that they may act as sunscreens. The red pigment 2 also has antibiotic activity: at concentrations lower than that found on the hippopotamus’s skin, it inhibits the growth of the pathogenic bacteria Pseudomonas aeruginosa A3 and Klebsiella pneumonia." (Saikawa et al. 2004:363)
About the inspiring organism
Med_ippopotami_lake_manyara_park hippopotamus
Hippopotamus amphibius Linnaeus, 1758
Common name: Hippopotamus

Learn more at
Some organism data provided by: ITIS: The Integrated Taxonomic Information System
Organism/taxonomy data provided by:
Species 2000 & ITIS Catalogue of Life: 2008 Annual Checklist

Bioinspired products and application ideas

Application Ideas: This idea could be applied to building exteriors or clothing to trigger release of non-toxic, UV-protection compounds when there is excess sun exposure, but only to the extent required to prevent UV damage.

Industrial Sector(s) interested in this strategy: Construction

Department of Applied Chemistry
Yoko Saikawa Masaya Nakata
Faculty of Science and Technology, Keio University
Molecular Spectroscopy Group
Vinicio Galasso
Department of Chemical Sciences, University of Trieste
Saikawa, Y.; Hashimoto, K.; Nakata, M.; Yoshihara, M.; Nagai, K.; Ida, M.; Komiya, T. The red sweat of the hippopotamus. Nature. 429(6990): 363.
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Galasso, V; Pichierri, F. 2009. Probing the molecular and electronic structure of norhipposudoric and hipposudoric acids from the red sweat of hippopotamus amphibius: A DFT Investigation. Journal of Physical Chemistry A. 113(11): 2534-2543.
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over 5 years ago
Thanks to Arno Vlooswijk for contributing the thermographic image of the hippo. The dark spots are droplets like sweat that have sunscreen and antibacterial properties.
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