Neanderthal glue recreated in a lab stopped staph bacteria growing in five of six batches tested

Tar cooked from birch bark by two Stone Age methods held back the growth of Staphylococcus aureus in laboratory dishes, according to a team led by Tjaark Siemssen, an archaeologist at the University of Cologne and the University of Oxford. The result suggests that a material long treated as a mere adhesive for stone tools may also have had a medical use.

The researchers recreated the tar from fresh bark, rather than recovering it from a Neanderthal site. Their release says “every type of birch tar they produced was able to inhibit the growth of Staphylococcus aureus,” a common cause of wound infections. That wording matters, because inhibiting growth in a dish is a weaker claim than killing bacteria, and the paper itself is more cautious than the summary.

Two Stone Age recipes for birch tar

Birch tar turns up at Neanderthal sites across Europe, often stuck to stone tools, which is why archaeologists long assumed it was mainly a Stone Age glue recreated in the lab for hafting, the sticky binder that joins a stone point to a handle. According to the University of Cologne’s account of the work, the team extracted tar from birch species present in the Neanderthal era using methods reconstructed from Neanderthal contexts. The first method places birch bark inside a sealed underground pit, where the lack of oxygen lets heat drive the tar out by dry distillation. The second burns bark beside a hard surface such as a stone, so that the tar condenses onto it. The ScienceDaily version of the release describes both as Stone Age production techniques, and the partners on the project were Oxford, the University of Liège and Cape Breton University in Canada.

The peer-reviewed paper, which was received in December 2025, accepted in February 2026 and titled “Antibacterial properties of experimentally produced birch tar and its medicinal affordances in the Pleistocene,” appeared in PLOS One in March 2026. It also tested a modern tin-can distillation, a third method that the release does not mention, and used two birch species, Betula pendula and Betula pubescens.

What the dish tests measured

The PLOS One paper used a disc diffusion assay, in which paper discs soaked in tar dissolved in a solvent are placed on a bacterial lawn and the clear ring around each disc is measured. Six tar samples were each tested in duplicate against a single strain of S. aureus, ATCC 25923, and the paper reports growth inhibition, not killing: it never describes the tar as bactericidal. Discs were 6 millimeters wide and loaded with 20 microliters of tar in a solvent, plates were incubated at 37 degrees Celsius for 24 hours, and the solvent alone served as a negative control. Tar yields from the burns were small, between 0.06 and 0.69 grams. The authors report inhibition zones from no effect up to 10.5 millimeters, and call the effect against the bacterium “moderate.”

Here the claim meets the data. According to the paper, five of the six samples held back the bacteria’s growth, producing rings of roughly 7 to 10.5 millimeters, while one sample, labeled BT3, showed no zone at all. The release’s “every type” therefore holds at the level of production method and tar type, not at the level of each individual batch. The gentamicin antibiotic used as a positive control produced rings of 22 to 23 millimeters, and the tar had no effect on a tested E. coli strain. Coverage of the study by ScienceAlert likewise noted that the tar was less effective than gentamicin and did nothing against E. coli, and it quoted only the study’s authors, with no independent expert.

What Neanderthals may have done with it

Siemssen frames the finding as a hint about behavior, not proof of it. In the university’s release he says, “The findings suggest that antimicrobial properties played a role as far back as the time of the early Neanderthals.” Matthias Bierenstiel, a chemistry professor at Cape Breton University and co-author, told ScienceAlert that the substance Neanderthals made 200,000 years ago “also possesses antibacterial properties.”

The experiments cannot show that anyone applied tar to a wound. The release states the limit directly, saying the result “does not necessarily mean that birch tar would be safe or effective as a treatment.” Sci.News adds that the tar was made from modern birch and that the link to Neanderthal use is inferred, with insect repellent among the other uses the authors raise. The same report says Indigenous communities in northern Europe and Canada use birch tar to treat wounds, and that the authors read their experiments as consistent with those practices, though the report attributes that reading to no named researcher beyond the author group. ScienceAlert adds that the tin-can method was inspired by Mi’kmaq practice.

Limits of a single-strain lab result

The paper calls itself exploratory and in vitro. It tested one S. aureus strain, did not chemically characterize the tar, so the active compounds are inferred rather than identified, and did not link production method clearly to potency. It also notes that published literature raises genotoxicity and polycyclic aromatic hydrocarbon concerns about birch tar, which the experiments did not assess.

Separate work on the same material comes from Delft University of Technology, where researchers, in a 2023 computational study of birch bark tar production, concluded that it likely required information processing beyond simple behaviors, though they stressed they could not prove which method Neanderthals used. Siemssen’s own suggestion for the next step is modest: he says it might be worthwhile to examine targeted antibiotics from ethnographic contexts. Whether tar made by any Stone Age recipe holds up against more than one strain, in more than six samples, remains an open question for the follow-up work.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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