Five of the six batches of Neanderthal glue the team made stopped staph from growing

Five of the six birch tar samples that a team led by Tjaark Siemssen of the University of Cologne and the University of Oxford made in the laboratory held back the growth of Staphylococcus aureus, a bacterium behind many wound infections. The sixth did nothing. Birch tar is the sticky black material that Neanderthals are known to have used as an adhesive, which is why the experiment is usually described as a test of prehistoric glue.

The day in tech, in one email: TLDR is the daily newsletter with links and TLDRs of the most interesting stories in startups, tech and programming.

Get TLDR →

We may earn a commission if you sign up.

The result is easy to overstate, and it has been. A popular summary of the work says every tar sample worked, but the paper itself reports one failure, along with a lot of detail about how modest the effect was next to a modern antibiotic. The distinction matters for a study whose headline claim is that an ancient material may have doubled as medicine.

Six samples, five with an effect on staph

The study appeared in PLOS One on March 18, 2026 as “Antibacterial properties of experimentally produced birch tar and its medicinal affordances in the Pleistocene.” The team made six samples, labeled BT1 to BT6, from the bark of two birch species, Betula pendula and Betula pubescens. The paper’s abstract lists three production methods: an underground pit, a condensation method and a modern tin can method. Yields were tiny, from 0.06 grams to 0.69 grams per sample.

Against S. aureus, the results varied. The paper reports that sample BT5, made with a raised structure method from B. pendula bark and tested at 133 milligrams per milliliter, “stood out” with the largest zone of inhibition, 10.5 millimeters give or take 0.7. Four others, BT1, BT2, BT4 and BT6, showed what the authors call moderate activity, with zones between 7.0 and 7.5 millimeters. One sample, BT3, “showed no activity,” a result the paper says mirrored its lack of effect on Escherichia coli.

A disc test with a gentamicin yardstick

The method is a standard one. A paper disc 6 millimeters wide is loaded with 20 microliters of tar dissolved in a solvent, set on a dish of bacteria and incubated at 37 degrees Celsius for 24 hours. If the tar stops growth, a clear ring appears around the disc, and the width of that ring is the measure. Each sample was run in duplicate. The solvent alone showed no inhibition, so the rings can be credited to the tar.

The yardstick was the antibiotic gentamicin, which produced zones of 22 to 23 millimeters against both bacteria. Even the best birch tar sample, at 10.5 millimeters, reached less than half of that. The paper calls the effect against the Gram-positive S. aureus moderate. Against E. coli, which has a different cell wall, no sample produced measurable inhibition; the reported 6 millimeters is simply the size of the disc.

What the release says and what the paper records

The University of Cologne announced the work on March 19, 2026, saying that all tar samples were effective at hindering the growth of S. aureus and that the effect appeared across all extraction methods. ScienceDaily reposted the release in October, which is the version that circulated again this fall. The release describes two reconstructed methods, dry distillation in a sealed underground pit and burning bark against a stone so the vapors condense on it, and does not mention the tin can method that the paper lists third.

The paper is more cautious than the summary. Its conclusion says that all three production methods showed “some level” of antibacterial properties, and its abstract says the efficacy is not related to the production method. Yet the results section says BT3 had no effect, and the text available does not say which method produced it. A failed sample from a method that otherwise worked is a normal outcome in a small experiment, and it is why a count of five of six is the safer statement.

From hafting glue to wound care

The wider claim rests on inference. As Archaeology Magazine reported on March 24, Neanderthals used tar as an adhesive to assemble tools, and Indigenous communities in northern Europe and Canada use birch tar to treat wounds today. Neither fact shows that Neanderthals did the same. Siemssen said in the release that the findings suggest antimicrobial properties played a role as far back as the time of the early Neanderthals, and the release itself frames wound care as something Neanderthals “may have” done.

The limits are written into the paper. The tests were run in dishes, not in wounds, and used only two bacterial strains. The authors did not chemically characterize the samples, so the active compounds are inferred, and they note that birch tar contains toxic and mutagenic compounds that limit its direct medical relevance. ScienceAlert’s April 5 coverage quotes co-author Matthias Bierenstiel of Cape Breton University, who said the substance Neanderthals made 200,000 years ago also possesses antibacterial properties. The experiments, in the words of the release, do not prove that Neanderthals applied birch tar to wounds.

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

The day in tech, in one email: Get TLDR →

We may earn a commission if you sign up.