In the peat swamps of Central Kalimantan, wild orangutans appear to do something long considered uniquely human: self-medicate.
A 20-year study published in Scientific Reports in mid-2026 found that Bornean orangutans consistently consume combinations of medicinal plants. These include species with antimicrobial, anti-inflammatory, and wound-healing properties. Their feeding patterns were also found to be far from random.
Around 30 percent of the 202 plant species in their diet are also recognized as medicinal by local Dayak communities.
The First Topical Treatment in Kalimantan
Evidence of this behavior had emerged long before the large-scale study was published. In 2017, a research team led by Helen Morrogh-Bernard, who later founded the Borneo Nature Foundation, documented Bornean orangutans chewing the leaves of Dracaena cantleyi without swallowing them.
Instead, the orangutans rubbed the chewed leaves onto their own arms and legs.
The same plant is used by local Indigenous communities to relieve muscle pain, joint pain, post-stroke pain, and swelling. At the time, however, the observation was regarded as an intriguing isolated case rather than evidence of a broader behavioral pattern.
A Wound That Healed Within a Week
Seven years later, further evidence emerged from a different island. In June 2022, a male Sumatran orangutan named Rakus suffered a facial wound. Researchers believe the injury was most likely caused by a fight with another male in Gunung Leuser National Park.
Three days later, researchers observed Rakus chewing the leaves of Fibraurea tinctoria. The medicinal vine has analgesic, antipyretic, and anti-inflammatory properties. It is also widely used in traditional medicine across the region to treat malaria.
Rakus did not swallow the chewed leaves. Instead, he repeatedly applied the pulp directly to his facial wound using his fingers. He continued until the wound was completely covered with the plant's juice and fibers.
Within a week, the wound had closed without any signs of infection.
A Pattern Too Consistent to Be Coincidental
The two cases raised an important question. Were these behaviors a genuine habit, or simply isolated incidents captured by chance?
A 2026 study led by Georgia Allen, a master's student at the University of Exeter, sought to answer that question on a much larger scale.
Working with Universitas Palangka Raya and CIMTROP, the team analyzed more than 20 years of behavioral records from the Orangutan Behaviour Project in the Sebangau peat swamp forest. They examined 12,236 feeding events from 55 identified orangutans, covering 202 different plant species.
The results were striking. Sixty-four of those food sources have documented ethnomedicinal uses and/or pharmacological properties.
Even more intriguing, several of these plants were not part of the orangutans' regular diet. Instead, they appeared only in specific combinations. Those combinations occurred far more frequently than could be explained by chance alone.
"Some plant species appeared together in the orangutan diet far more often than we would expect by chance," Allen wrote.
She added that the selection of these plants appears to go beyond ordinary nutritional needs.
The findings became even more significant because they closely overlapped with human knowledge. Nearly one-third of the 202 plant species had already been recognized as medicinal by Dayak communities, long before researchers documented them systematically.
Orangutans and humans diverged from a common ancestor millions of years ago, long before the earliest written records of human medicine. Yet both species, independently, identified many of the same medicinal plants in the same forest.
