A Rhino's Horn Is Made of the Same Stuff as Your Fingernails

Rhino horn sells, illegally, for sums that have at times been quoted alongside gold by weight. The demand rests largely on a belief that it has medicinal properties.

The awkward biological fact underneath the entire trade is that a rhino horn is made of keratin. The same structural protein as your fingernails, your hair, and a horse's hoof.

It Is Not a Horn, Technically

Three things get called horns and they are built differently.

Antlers, as on deer, are bone. They grow from the skull, are covered in living velvet while developing, then die, and the animal sheds them and grows a new set annually.

True horns, as on cattle, sheep and antelope, are permanent. They have a bony core growing out of the skull with a keratin sheath over it. Cut one badly and you are into living bone.

Rhino horn is neither. There is no bony core at all. It grows from the skin, from a dense patch of tissue on the skull, and it is keratin all the way through. Structurally it is closer to a very large, very compacted callus than to anything on a cow.

Work by Hieronymus and Witmer described the internal structure as a mass of tightly packed keratin filaments, with the core containing deposits of calcium and melanin. Those deposits appear to serve a purpose: the calcium hardens the centre and the melanin absorbs ultraviolet, so the outside weathers away faster than the middle. Over a lifetime of use and sun that differential wear is part of what keeps the horn pointed.

Which Means It Grows Back

This is the part with real consequences. Because there is no bone in it and it grows continuously from the base, a rhino horn regrows if it is cut, provided the cut stays above the growth plate.

That is the basis of dehorning as a conservation measure. Reserves under heavy poaching pressure sedate rhinos and trim the horn, on the reasoning that an animal without a marketable horn is not worth a poacher's risk. It has to be repeated every couple of years as the horn regrows.

It is not a clean solution and nobody involved pretends otherwise. Dehorned rhinos have still been killed, sometimes for the stub, sometimes apparently so the poacher does not waste time tracking the same animal again. There are behavioural costs too, since rhinos use horns for defence against predators and in disputes with each other. The sedation itself carries risk. It is a measure taken because the alternative is worse, not because it is good.

The Medicine Claim

The traditional use is generally as a ground powder taken for fever and other conditions. It has been studied, and the results are what the chemistry predicts.

Keratin is a structural protein. It is not readily digestible and has no established pharmacological activity of the kind claimed. Consuming rhino horn is, in terms of what your body actually receives, closely comparable to consuming fingernail clippings. That comparison gets repeated often enough to sound like a rhetorical flourish, and it is not one. It is roughly accurate.

More recently, a substantial share of demand has shifted from medicinal use to status display, with carved horn and whole horns held as luxury goods and investments. That is a harder problem for a public information campaign, because it does not rest on a factual claim that can be corrected.

Where That Leaves Them

Five species survive. The white and black rhinos in Africa, and the greater one-horned, Javan and Sumatran rhinos in Asia. The Javan and Sumatran populations are down to numbers small enough that individual animals matter to the species' survival. The northern white rhino is functionally extinct, with two females left and no males.

The greater one-horned rhino is worth knowing about as a counterweight, because it has recovered substantially from a few hundred animals under sustained protection in India and Nepal. The decline is not inevitable. It is just expensive to stop.

Sources

• Hieronymus, T. L., Witmer, L. M. and Ridgely, R. C. (2006). Structure of white rhinoceros horn investigated by X-ray computed tomography and histology. Journal of Morphology.
• Emslie, R. and Brooks, M. (1999). African Rhino: Status Survey and Conservation Action Plan. IUCN.
• Ferreira, S. M., Greaver, C., Knight, G. A. et al. (2015). Disruption of rhino demography by poachers. PLoS ONE.
• IUCN SSC African and Asian Rhino Specialist Group status reporting.