Hippos, Horses Sweat ... and More Smelly Secrets

Perspiration in the animal kingdom is often not just a simple sweat and stink process, as new research demonstrates. Horse sweat, for example, turns out to contain a natural detergent, appropriately named latherin, which does indeed lather and function like soap.

Malcolm Kennedy of the University of Glasgow and colleagues report in the latest Journal of the Royal Society Interface that latherin probably evolved, first as a protein ingredient in saliva to help process dry fibrous foods, and then later was "recruited to the skin as equids evolved into large-bodied flight animals capable of sustained exercise requiring rapid onset and efficient heat dissipation." Latherin, among other functions, "facilitates spreading of the sweat over the oily pelt of the horse."

It's a myth that guinea pigs do not have sweat glands. A number of studies document the branched sweat glands in guinea pigs and other animals. These glands do not, however, function as ours do, such that guinea pigs are susceptible to heat stroke. They also possess no sweat glands in the hairless areas behind their ears.

Another myth is that wild boars do not possess sweat glands. They do, but the glands again don't function like ours do. Marc Bracke of Wageningen University and Research Centre believes that "wallowing (in mud) could be an important element of a good life in pigs," making them happy and cooling them down as sweat otherwise would. Pigs might smell like mud and poo at times, but they don't have sweat-created body odor.

According to the ASPCA, "man's best friend really does sweat through his footpads. Paw sweating is one of the ways dogs keep cool on a hot summer day, but it's not the most important. Dogs can also pant to cool down, and they have some other tools in their bodies to beat the heat as well."

On a hot day, notice how cats might leave little wet footprints. That is likely sweat coming out of their paws. Felines otherwise cool themselves down by licking. The evaporation cools and cleanses at the same time. One perk of cat ownership: Their bodies rarely stink.

According to Ken Caldeira of the Carnegie Institution's Department of Global Ecology, plants give off water through tiny pores in their leaves, a process called evapotranspiration. This cools the plant, just as perspiration cools our bodies. He notes that on a hot day, a tree can release tens of gallons of water into the air, acting as a natural air conditioner for its surroundings.

Perhaps the most unusual sweat in the animal kingdom comes from hippos. A research team from Kyoto Pharmaceutical University recently determined that the oily substance, containing orange and red pigments, is antibacterial, prevents sun damage and regulates temperature. Onlookers first thought hippos secreted blood, due to the substance's color.

Great white sharks and other marine dwellers do not sweat. They are surrounded by water already, so adding water to their skin would not help to regulate their body temperature. Bony fish do get thirsty, though, and drink a lot of water. That's because osmosis results in loss of body water (since their blood contains salt), which must be replenished.

Macaques and other non-human hairy primates do have sweat glands on their bodies, but no one will ever see such an animal dripping in sweat. Fur serves as a barrier between the glands and the environment. As a result, these animals maintain more constant body temperatures. Monkeys, for example, do not feel cold like we humans do after bathing.

In terms of sweat body odor, humans could very well be the smelliest species on the planet. Body odor is a cue for health and plays a more important role in mate selection than most of us realize. A study recently published in the Proceedings of the Royal Society B found that people enjoy their own body odor and gravitate to perfumes and colognes that match and enhance the individual's unique smell.