Birch tar, the Neanderthals' glue and antibiotic?

It is a black, sticky substance with an acrid smell of smoke. For decades, archaeologists have found it on Neanderthal stone tools, where it was used to fix a point onto a wooden handle. Birch tar is considered the oldest glue ever made by humans. But a study published in the journal PLOS One, and highlighted on 10 October 2026 by the University of Cologne, suggests that it may also have healed. Made using techniques available to Neanderthals, this plant tar slows the growth of Staphylococcus aureus, a bacterium responsible for many wound infections.¹²

Behind the discovery is Tjaark Siemssen, an archaeologist at the universities of Cologne and Oxford, working with chemists and microbiologists from the University of Liège and Cape Breton University in Canada. Their question was simple: what if our vanished cousins knew not only the adhesive power of this material but also its medicinal virtues?¹

The oldest glue in the world

Birch tar is obtained by heating birch bark without air. Under the heat, the bark, rich in betulin and related compounds, breaks down and releases a thick black liquid that hardens as it cools. When reheated, it becomes pliable again. It is therefore an ideal thermoplastic glue for haftinghaftingThe way a blade or point is fixed onto a handle or shaft, a key stage in making a composite tool.→ a tool: it is applied hot, the stone is pressed into it, and the joint sets.

The oldest traces of birch tar are associated with the Neanderthals of Europe and date back about 190,000 years.³ In Italy, at the site of Campitello in Tuscany, two flint flakes have kept remains of the tar that fixed them to their handles. In Germany, at Königsaue, lumps of tar still bear the imprint of a tool and even that of a fingerprint. And in the Netherlands, a flint flake dredged up off the coast, on the Zandmotor, carries a coating of tar dated to around 50,000 years ago. These finds show that NeanderthalsNeanderthalsA fossil humanity of Eurasia, robust and cold-adapted, extinct around 40,000 years before present.→ mastered a fire-based transformation technique long before the invention of pottery or metallurgyMetallurgyThe techniques of extracting and working metals (copper, bronze, gold); its rise in the Eneolithic and Bronze Age transformed tools, weapons and social hierarchies.→.

A debated technical feat

For a long time, tar-making was presented as proof of the advanced intellectual abilities of Neanderthals. To obtain the tar, the bark has to be heated to roughly 340 to 400 degrees Celsius without catching fire, which seemed to require a closed container. Yet Neanderthals had neither pottery nor fireproof vessels.

In the 2010s, several teams therefore tried to reproduce birch tar using only the means available in the Middle PalaeolithicPalaeolithicThe oldest and longest period of prehistory (c. 3.3 Ma–12,000 BC), defined by chipped stone tools and a hunter-gatherer way of life.→Middle PalaeolithicA Palaeolithic period (c. 300,000 to 40,000 years ago) associated mainly with Neanderthals and early Homo sapiensHomo sapiensThe present-day human species, which emerged in Africa around 300,000 years ago, the only surviving human lineage after the extinction of Neanderthals and Denisovans.→, marked by Levallois tools.→. They showed that simple methods work: burying rolled bark under a layer of embers, or burning it against a stone on which the tar condenses. These experiments fuelled a debate: was birch tar the product of complex planning or an almost accidental discovery at the edge of the hearthhearthA combustion structure set on the ground, evidence of the mastery of fire and a marker of how a prehistoric dwelling was organised.→? Either way, the quantity of tar needed to haft tools on a regular basis implies controlled and repeated production.

Three ways to make tar

For their new study, Tjaark Siemssen and his colleagues collected bark in Germany from two species present in Europe during prehistoryPrehistoryThe span of human history before the invention of writing, from the Palaeolithic to the Metal Ages, known mainly through material remains.→, downy birch and silver birch. They then produced tar using several methods.¹³

The first method follows a technique used by the L'nu, or Mi'kmaq, of eastern Canada: bark is placed in a pierced metal tin and heated, and the tar drips into a container below. The L'nu use this tar, called maskwio'mi, as an ointment for wounds and skin conditions. This method, which relies on metal, was obviously not available to Neanderthals, but it served as a reference.³

The other two methods require nothing more than earth, clay, stones and fire. In the first, a container is placed at the bottom of a pit, covered with tightly packed dry bark and a thin layer of clay, and a fire is then burned on top for about two hours before the tar is collected. In the second, a small amount of bark is burned beneath a fireproof stone, on whose surface the tar condenses. This is the simplest method, but also the one that yields the least material.³ "Every step of the production is a sensory experience in itself," says Tjaark Siemssen, who admits that getting the tar off his hands after hours by the fire was a challenge every time.²³

A targeted effect on staphylococcus

The tar samples were then exposed to two very common bacteria: Staphylococcus aureus and Escherichia coli. The result is clear for the first. According to the University of Cologne, all the samples made with prehistoric methods inhibited the growth of staphylococcus, whichever process was used.¹

The effect nonetheless varies with the birch species and the technique. The most effective sample was made from silver birch using the pit method. The others proved mildly to moderately active, and one downy birch sample produced by condensation had, according to a detailed account of the study, almost no effect.³ As for Escherichia coli, the tar did not seem to bother it. This selectivity is not surprising: staphylococcus belongs to the so-called Gram-positive bacteria, which are generally more sensitive to plant compounds than Gram-negative bacteria such as E. coli, protected by an additional outer membrane.

And Staphylococcus aureus is precisely one of the main culprits behind skin infections and festering wounds. For hunters exposed to injuries, to cuts while knappingknappingThe set of operations for fracturing a stone block to extract flakes or blades.→ flint or butchering game, such a remedy could have made the difference between a wound that heals and a dangerous infection.

Neanderthals as healers?

The idea that Neanderthals cared for themselves is no longer far-fetched. Several skeletons bear traces of serious injuries that healed, implying that the injured were fed and protected during their recovery. Analysis of the dental calculus of Neanderthal individuals has revealed the consumption of bitter plants with no nutritional value, such as yarrow and chamomile. At El Sidrón in Spain, an individual suffering from a dental abscess appears to have consumed poplar, which contains salicylic acid, and a mould that produces antibiotic substances.³

Birch tar would fit into this pharmacopoeia. "Antimicrobial properties played a role as far back as the time of the early Neanderthals," says Tjaark Siemssen, who believes they may have been exploited in a targeted way.¹ In his view, the results have important implications for understanding how Neanderthals may have reduced the burden of disease during the last Ice Age.² The researcher also acknowledges that such a hypothesis would have met with far more scepticism thirty years ago.³

Knowledge shared by many peoples

The medicinal use of birch tar is not an archaeologists' invention. In northern Europe as in Canada, Indigenous communities traditionally use it to treat wounds and skin complaints.² In Europe, birch tar was long used in folk and veterinary medicine, notably in ointments for skin conditions.

Birch tar was also chewed. Lumps of tar bearing tooth marks have been found at several MesolithicMesolithicThe period between the Palaeolithic and the Neolithic (c. 10,000–6,000 BC in Europe), still based on hunting and gathering.→ and NeolithicNeolithicThe "New Stone Age": a period marked by farming, herding, settlement and pottery, from around 10,000 BC.→ sites in Scandinavia. In Sweden, a study published in 2024 showed that tar "chewing gums" 9,540 to 9,890 years old had been chewed by three children and three teenagers.³ We do not know whether these young hunter-gatherersHunter-gatherersA way of life based on hunting, fishing and gathering wild resources, without farming or herding; it dominated almost the whole of human history.→ were softening the tar to make glue, chewing it for pleasure, or easing toothache or sore gums. Much later, Ötzi, the Iceman who died around 5,300 years ago, used birch tar to fix the points of his arrows and the blade of his copper axe.

The limits of the experiment

The researchers themselves remain cautious. The study demonstrates in the laboratory that tar made by prehistoric methods has antibacterial activity. It does not prove that Neanderthals applied it to their wounds, nor that the remedy was safe or effective in humans.¹

Archaeologist Karen Hardy of the University of Glasgow, who was not involved in the study, points out that producing birch tar is a long and complex process. To conclude that it was made deliberately for medicine, one would need to show that it offered a real or unique advantage over other remedies that were easier to obtain.³ Other plants available to Neanderthals do have antiseptic properties, and the tar could also have served as an insect repellent. The authors themselves call for wider research into these multiple uses.²

Another difficulty lies in the remains themselves. At archaeological sites, birch tar is almost always found on tools, where it served as glue. An ointment spread on a wound leaves no lasting trace. Direct proof of Neanderthal medical use will therefore probably remain out of reach. The study does, however, open up a possibility: that in making their glue, Neanderthals handled a product with protective properties every day, and that they may well have noticed.

Ancient remedies for modern ills

Beyond prehistory, the study echoes a very current concern: the growing resistance of bacteria to antibiotics. Methicillin-resistant Staphylococcus aureus, or MRSA, is one of the most feared germs in hospitals around the world.²

For Tjaark Siemssen, it might be worthwhile to examine targeted antibiotics from ethnographic contexts, in other words the traditional remedies handed down by the peoples who have used them for generations.¹ Birch tar is no miracle drug, but it is a reminder that the human pharmacopoeia is vastly older than modern medicine.

So a black, sticky glue, long regarded as a simple witness to the technical skill of Neanderthals, may also reflect their attention to care. Between the workshop and the pharmacy, the boundary may already have been thin two hundred thousand years ago, around the fires where birch bark slowly turned into tar.