Wednesday, May 26, 2010

The red "sweat" of hippos

Nope, hippos don't sweat - not in the strictest sense, as the red "sweat" of a hippo is not secreted by sweat glands. Anyway, the "sweat" of a hippo was speculated to help control the animal's body temperature, just like the sweat we produce.

After seeing the hippos in Paya Indah Wetlands, I googled for interesting information about hippos and stumbled on an interesting article about hippo "sweat". According to the three Japanese scientists who wrote the report, the red "sweat" of hippos is secreted from "unknown subdermal glands". Whatever those are, they are not sweat glands.

When first secreted, the red "sweat" is viscous and colorless. After a couple of minutes, the secretion turns red, and eventually brown after a few hours. The Japanese research team isolated the pigments responsible for the color change in the "sweat" and named them "hipposudoric acid" (the red pigment) and "norhipposudoric acid" (the orange pigment).

What's amazing about the hippo's red "sweat" is that it is a natural sunscreen and antiseptic - thanks to the red and orange pigments! The pigments can absorb harmful ultraviolet rays (290-400 nm) which reach the ground. Also, the pigments inhibit the growth of pathogenic bacteria Pseudomonas aeruginosa and Klebsiella pneumoniae. The antibacterial role of the "sweat" probably explains why hippos manage to have scratches and wounds in their skin cured readily, rarely infected, despite spending so much time in the mud (apparently an unsanitary environment).

Journal reference:
Kimiko Hashimoto, Yoko Saikawa, and Masaya Nakata (2007) Studies on the red sweat of the Hippopotamus amphibius. Pure Appl Chem, Vol. 79, No. 4, pp. 507–517.