Ever since I was little, one of my favorite holiday carols has been the slightly lesser known “I Want a Hippopotamus for Christmas.” Believe it or not, like the little girl singing the song, I often hoped a hippopotamus would be standing under my family tree come Christmas morning. During trips to the zoo, I can always be found spending large quantities of time watching the hippos.
But one of the things that really got my attention during one of my more recent zoo outings is how appropriately festive hippos are for the Christmas season – much like Rudolph’s nose, they have the ability to turn bright red. But since the job is obviously taken, this unique characteristic isn’t used to lead Santa’s sleigh. As an alternative to investigating the presents already sitting under my family Christmas tree in the hopes of finding a wrapped hippopotamus, I decided to investigate the reasons behind the red secretion of the hippo.
If “The Nightmare Before Christmas” is more your style, the red secretion of hippopotamuses has led to folktales of hippos secreting blood. Fortunately, the color change is not actually due to any sort of blood loss. In fact, it is commonly known as “red sweat.” However, it really isn’t sweat, because hippos do not have sweat glands; it is an oily red liquid secreted by different glands under the hippo’s skin. The red sweat appears in greater quantities during the day, suggesting a role in helping the hippo regulate its body temperature. Also, higher quantities of red sweat seem to be correlated with agitation, much like humans can sweat when experiencing various emotions. (I told you hippos had feelings too, Mom!)
Numerous studies have been conducted in an attempt to determine the exact function of the red sweat in hippos. Like human sweat, the evaporation of red sweat from the hippo body results in evaporative cooling. In this way, the red sweat helps the hippopotamus regulate its temperature in its naturally hot desert habitat.
Research has also shown that red sweat has antibiotic, antiseptic, and sunscreen properties. While hippos may seem rather fat, their skin is actually thin, for flexibility purposes. However, this makes hippo skin more vulnerable to fungal and bacterial parasites in the aquatic environment. Luckily, the skin appears to heal quickly from injury, due to its inhibition of bacterial growth. The red sweat can also serve a cleansing function, as it tends to scour mud off the hippopotamuses when they are on land. The absorbant properties of the red pigments in the liquid protect the hippopotamus from UV rays and allow it to remain in the sun for long periods of time without enduring significant damage to its skin. Serving so many functions, hippopotamus red sweat is truly unique!
For all you children out there who want a hippopotamus, you may have a chance: go ahead and tell your mother that you won’t need to put sunscreen on your hippopotamus before taking it for walks, it’s self-cleaning, and it will coordinate nicely with your Christmas decorations.