Hippos Sweating Blood

I am not from an area with a particularly warm climate. In the summer it can be really warm but the heat doesn’t last for a long time. Whenever it‘s super warm I normally hide in the shade or the air conditioning. If I’m going to be outside for a long time I need to put sunscreen on and I know I’m going to be sweating, both of which are necessary but annoying. The hippo (Hippopotamus amphibious) has adapted in a way that when it sweats it is protected from ultraviolet rays.

When a hippo sweats it looks like it's sweating blood. However, when hippos are hot the substance they produce is not strictly sweat. Hippos will secrete a substance that is a thick clear liquid that changes to a red-brown colour after a few minutes. Two chemicals have been extracted from this liquid each having its own pigment, one red and one orange. The red pigment acts as an antibiotic protecting the hippo from infection. The orange pigment blocks a good portion of ultraviolet and visible spectrum rays (Saikawa et al., 2004).

Sweat glands are found only in the skin of mammals and appear to be controlled by the nervous system. They have different functions including thermoregulation, protection against frictional damage, acting as scent glands, and bacterial actions (Jenkinson, 2006). Hippos are native to central Africa which is constantly under direct sunlight and heat (Gowland, 2004). With the chemical with the orange pigment in their skin hippos are able to withstand being out in the sun for long periods of time. Male hippos are also aggressive towards each other in order to mate with a female. Because of this sexual competition, the ability of the red pigment in their sweat helps the hippos avoid getting infections and allows them to continue to search for mates.

Here’s a video with hippos sweating and some other fun facts:

References:

Gowland, F 2004, ‘Hippos lead the way in multipurpose sun screen’, Journal of Experimental Biology, vol. 207, no. 19, pp. 4-7, doi:10.1242/jeb.01196.

Jenkinson, DM 2006, ‘Comparative physiology of sweating’, British Journal of Dermatology, vol. 88, no. 4, pp.397-406, doi:10.1111/j.1365-2133.1973.tb07573.x.

Saikawa, Y, Hashimoto, K, Nakata, M, Yoshihara, M, Nagai, K, Ida, M & Komiya, T 2004, ‘Pigment chemistry: The red sweat of the hippopotamus’, Nature, vol. 429, no. 363, doi:10.1038/429363a.