Stinking hair keeps parasites at bay.
"For years, zookeepers and hunters have noted that giraffes have this overpowering aroma," says biologist William Wood. In South Africa, old male giraffes are nicknamed stink bulls and some people claim you can smell the animals up to 250 metres away.
Now Wood thinks he has pinned down the pong's purpose. The rank-smelling chemicals in giraffe hair include a range of antibiotics and parasite repellents, he has found, working at Humboldt State University, Arcata, California1.
"This is one of the first studies looking at [chemical defences in] mammal hair," says immunologist Valerie Smith of the University of St Andrews, UK. Many animals, including humans, produce microbe-busting compounds, but they are more commonly deployed in sweat or skin, she says,
It's not known how the giraffe makes its pelt reek. The animal could produce the chemicals in sweat or oil glands in the skin, and incorporate them into the growing hair, Wood suggests.
Unfortunately, he adds, giraffes' protective perfume is unfit for human consumption: "It stinks terribly - you wouldn't want to put it on you."
Wood scraped hair from the neck and back of a zoo giraffe (Giraffa camelopardalis reticulata), and, with his colleague Paul Weldon, analysed its composition. The hair turned out to have 11 main smelly chemicals.
Giraffes' scent is mainly due to indole and 3-methylindole. These compounds give faeces their characteristic whiff, and are known to stunt the growth of microbes such as the fungus that causes athlete's foot and the bacterium Staphylococcus aureus.
Several other of the chemicals work against fungi and bacteria on skin. Some become more effective when mixed with others in the brew. Another, para-cresol - found in creosote - repels bloodsucking ticks.
A giraffe's scent probably serves a sexual function too, says Wood, as males smell stronger than females. Smith agrees: "Males could be saying 'there're no fleas on me'," she says.
Wood has discovered, and patented, a bacteria-killing chemical produced by glands between the toes of the black-tailed deer. Several other animal-made antibiotics are reaching clinical trials.
Wood, W. F. & Weldon, P. J. The scent of the reticulated giraffe Giraffa camelopardalis reticulata. Biochemical Systematics and Ecology, 30, 913 - 917, (2002).
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Whitfield, J. Rank giraffes in rude health. Nature (2002). https://doi.org/10.1038/news021014-13