What are rhino’s horns made of? Rhinoceros Facts & Frequently Asked Questions

As a nature know-it-all kid, I loved talking to (more likely at) people about my favorite animals. One of those favorites was the rhinoceros, a dinosaur-like animal I loved to watch on nature shows. My go-to trivia fact was that rhino horns were not bones, but actually “made of hair”. Thanks to a recent reader request, we’ve now come full circle, and I’m delighted to return to this question for a more in-depth perspective. While seven-year-old me was correct that rhino horns are not bone, the story is a bit more complicated than them being made of hair. In this Science Deep Dive post, let’s dig into the science of rhinoceros horns and learn some cool rhino facts along the way.

What are rhino horns made of?

To get straight to it: rhinoceros horns are composed primarily of keratin, which is the same structural protein making up much of our hair and fingernails. However, they have a pretty complex structure by comparison. While the horns of many animals actually grow around a core of real bone, rhino horns form from keratin secreted by specialized cells around a “core” of calcium and the protein melanin. This core provides the structural support enabling the horn to maintain a given shape. It also allows the different parts of the horn to wear away at different rates, creating a sharpened point. Science communicators often liken this to the way a pencil gets sharpened, although the metaphor isn’t exactly perfect!

Scientists disproved the common claim that rhinoceros horns are made of bunched-up hair as early as the 1960’s. Technological advancements like scanning electron microscopy enabled more in-depth investigations, leading to the discovery that they consisted of hairlike filaments linked around a central core in what engineers would call a composite. Researchers have observed that this is very similar to horse hooves and bird beaks, rather than cow horns, for example.

Read more: What’s the difference between horns and antlers?

How do rhino horns grow?

A study in 2015 shed light on how these amazing horns grow. The skin around and underlying the horn is different than skin on the rest of the rhino’s body, and includes dermal papillae, which are extensions of deep-skin tissue that extend up into the outer skin (epidermis). Essentially, these papillae produce the keratin-based fibers that make up the horn, secreting the protein much like the nailbed under the skin of our fingers that forms fingernails. In this case, a more complex network of linked and interacting papillae in a circular pattern produce both the core and the surrounding fibers. Rhino horns can grow about 3/4 of an inch (2cm) per year.

Do rhino horns keep growing forever?

Yes! Just like our fingernails, rhinoceros horns are continually growing, and continually being worn away by regular use. Since rhinos have relatively long life spans (around 30-50 years), these horns can get quite long. A black rhino (Diceros bicornis) horn found in Kenya holds the record at over 4 feet (1.3m!)

What are rhino horns for?

Rhinos use their horns as daunting weapons during aggressive interactions with counterparts or other perceived threats, especially when protecting calves. Horns also are used in foraging behavior to break branches and for disrupting soil to form mud wallows or find water. 

Do both male and female rhinoceroses have horns?

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