Propolis: What Bees Make From Tree Resin

Every beekeeper has a propolis story, and it always involves something getting permanently stuck to something else.

Propolis is the brown, resinous substance that honey bees collect from tree buds, sap flows, and botanical sources, then mix with beeswax, enzymes, and their own secretions to create a material that functions as the colony's combination caulk, antiseptic, and immune system. It contains more than 200 identified chemical compounds. It smells like a forest floor mixed with honey. It has the adhesive properties of industrial epoxy at hive temperatures and the brittleness of hard candy when cold. And beekeepers scrape it off everything - frames, hive tools, gloves, clothing - with the resigned acceptance of people who have given up fighting a substance that has been outsmarting humans for several thousand years.

The ancient Egyptians used it to preserve mummies. Italian violin makers may have used it to coat Stradivarius instruments. Modern researchers have found it kills antibiotic-resistant bacteria. And somewhere right now, a beekeeper is trying to get it off their truck's steering wheel.

What It Actually Is

Propolis composition varies by geography because bees use whatever's locally available, and trees in Michigan produce different resins than trees in Brazil. But the general breakdown runs approximately 50% plant resins, 30% waxes, 10% essential oils, 5% pollen, and 5% organic compounds. That last 5% is where things get interesting.

The organic compound fraction includes flavonoids - particularly pinocembrin, galangin, and chrysin - phenolic acids, terpenes, and aromatic compounds that collectively give propolis its biological activity. These aren't random plant chemicals the bees happened to collect. The resin sources bees select are specifically those with antimicrobial properties. Poplars, birches, willows, conifers, and horse chestnuts produce resins that discourage microbial growth on their own wounds. The bees harvest these resins and concentrate them.

The word "propolis" comes from Greek: "pro" (before, in front of) and "polis" (city). Before the city. In defense of the city. Which is exactly how bees use it - they coat the interior of the hive entrance with propolis, creating what amounts to an antimicrobial doormat that every bee walks through on the way in.

The Propolis Envelope

This is where the research gets remarkable.

Marla Spivak and Renata S. Borba at the University of Minnesota published findings in 2017 that documented what they called the "propolis envelope" - the thin coating of propolis that bees apply to the interior walls of their hive cavity. Wild colonies living in tree hollows coat the rough interior surfaces extensively with propolis. Managed colonies in smooth-walled hive boxes deposit significantly less.

The researchers tested what happens when colonies with and without propolis envelopes are exposed to American foulbrood - one of the most devastating bacterial diseases in beekeeping, caused by the spore-forming bacterium Paenibacillus larvae. Two months after infection, colonies with a propolis envelope had 52% fewer cells infected with AFB compared to colonies without.

Fifty-two percent. From a coating the bees applied themselves, using materials they collected from trees.

The mechanism is what scientists call "social immunity" - a collective behavior that benefits colony health without requiring individual bees to mount expensive immune responses. The propolis envelope reduces the ambient pathogen load inside the hive, which means individual bees spend less energy fighting infections. Their immune systems can be smaller, metabolically cheaper, redirecting resources toward foraging, brood rearing, and everything else a colony needs to survive.

Research published in the Proceedings of the Royal Society B added another dimension: bees use propolis as a natural pesticide specifically against varroa mites. The study found that propolis is applied to brood cells where it directly affects reproducing parasites. Propolis significantly increased varroa mortality, approaching 20% in treated cells. And when colonies detect varroa infestations, they actually increase their resin foraging rates - they collect more propolis because they need more propolis. The colony is, in a meaningful sense, self-medicating.

Embalming the Pharaohs (And Everything Else)

The historical use of propolis predates written records, but the written records that exist are striking.

Ancient Egyptian priests soaked bodies and bandages with a mixture of melted honeycomb - wax, honey, and propolis combined - as a preservative agent in mummification. Propolis was one of the primary ingredients in the embalming recipe. The antimicrobial properties that protect a bee colony from bacteria also, it turns out, prevent a human body from decomposing. The Egyptians didn't know the biochemistry. They knew it worked.

Aristotle provided the first specific written reference to propolis in his studies of the honeybee. The Greeks continued the Egyptian tradition of using honey and propolis to preserve bodies - Agesipolis, the Spartan king who died in Asia, was preserved in honey for transport home, as was Alexander the Great.

Roman soldiers carried propolis to war for wound treatment. During the Boer War in South Africa (1899-1902), propolis preparations were used to treat battle wounds. The Soviet Union used propolis-based preparations extensively in World War II military hospitals - calling it "Russian penicillin" - at a time when actual penicillin was in desperately short supply.

And then there's the violin connection. Propolis has been used as a ground coat in classical violin making - the base layer applied to bare wood before varnish. Dissolved in warm alcohol, filtered, and combined with alum, propolis creates a bright yellow preparation that fills tool marks and wood pores while producing the characteristic golden ground visible under the varnish of old Italian instruments. Whether Stradivari himself used propolis remains debated (recent chemical analysis of his varnish identified drying oil, pine resin, and pigments but not definitively propolis), but the use of propolis in luthier workshops is documented and ongoing.

A substance collected from tree buds by an insect, used to mummify pharaohs, possibly coat Stradivarius violins, and treat soldiers' wounds across three centuries of warfare. The range of applications is genuinely absurd.

What the Lab Says

Modern antimicrobial research on propolis reads like the results section of a paper nobody expected to be this interesting.

Studies on propolis activity against MRSA (methicillin-resistant Staphylococcus aureus) - the antibiotic-resistant bacteria that haunts hospital wards worldwide - found that quercetin and its derivatives in propolis demonstrated antibacterial efficacy against MRSA, S. epidermidis, and S. aureus. Mediterranean propolis extracts showed effectiveness at concentrations of 100 to 1,000 micrograms per milliliter.

The mechanism involves interference with penicillin binding protein expression, disruption of ATP synthesis in bacteria, and destabilization of bacterial membrane integrity. When combined with conventional antibiotics, propolis extracts reduced bacterial resistance - the synergistic effect meant the bacteria that had evolved to shrug off standard drugs were suddenly vulnerable again.

Antiviral results are equally striking. Brazilian green propolis reduced SARS-CoV-2 viral load by 67-87% at tested concentrations. Bulgarian propolis suppressed replication of H3N2 and H1N1 influenza viruses in vitro. Six separate clinical trials found propolis more effective against herpes viruses than acyclovir - the standard pharmaceutical treatment. A propolis flavonoid ointment at 300 milligrams per milliliter showed improved healing and reduced infection rates compared to both acyclovir and placebo.

The chemical complexity - more than 200 identified compounds - makes propolis difficult to standardize pharmaceutically, which is why "propolis-based antibiotic" hasn't appeared on pharmacy shelves. The composition varies with geography, season, and source plants. Brazilian green propolis has different chemistry than European propolis, which differs from Asian propolis. The active compounds work synergistically, meaning isolating individual components reduces effectiveness. Nature's antimicrobial cocktail resists being turned into a single-molecule drug.

The Economics of Sticky

Propolis yields from managed hives are modest. A typical colony produces 100-300 grams of propolis per year - some sources cite up to 400 grams under favorable conditions. Commercial propolis harvesting uses specialized traps: plastic or wooden grids with small gaps that bees instinctively fill with propolis, which the beekeeper removes and freezes (making it brittle enough to crack off the trap).

Raw propolis prices vary significantly by origin and quality. Brazilian green propolis - considered the premium source due to its high concentration of Artepillin C and other bioactive compounds - commands substantially higher prices than generic propolis. The global propolis market has expanded steadily, driven primarily by demand from the supplement, cosmetics, and pharmaceutical industries.

Propolis tinctures (alcohol extracts) sell retail for $15-40 per ounce, depending on concentration and origin. Propolis supplements in capsule form range from $10-30 per bottle. Raw propolis sells for $10-60 per pound depending on quality and source. The markup from raw material to finished supplement is considerable - a beekeeper selling raw propolis at $30 per pound sees a dramatically different return than a supplement company selling the same material in capsule form at $25 for 60 capsules containing 500 milligrams each.

The economic irony is familiar to beekeeping: the most scientifically interesting product of the hive is a minor revenue stream compared to honey, and most beekeepers treat it as a nuisance that gums up their equipment rather than a harvestable commodity. The same substance they spend weekends scraping off frames with a hive tool could be frozen, bagged, and sold to supplement companies.

The Beekeeping Contradiction

Here's the thing that makes propolis strange from a hive management perspective.

Modern beekeeping equipment - smooth, milled, painted wooden boxes - actively discourages propolis deposition. Bees coat rough surfaces enthusiastically and smooth surfaces minimally. The propolis envelope that Spivak's research identified as reducing AFB infection by 52% forms much more extensively in wild hive cavities with rough bark interiors than in manufactured Langstroth boxes.

Commercial beekeeping has spent a century making hive equipment that's easy to clean, easy to manipulate, and smooth enough that frames don't stick together. In doing so, the industry inadvertently reduced the colony's ability to build its own antimicrobial defense system. The scraped propolis that beekeepers curse isn't a flaw in the colony's design - it's the immune system trying to assert itself against equipment that wasn't built to accommodate it.

Some researchers have proposed roughening the interior surfaces of hive bodies to encourage propolis envelope formation - essentially making the boxes more like tree cavities. The idea has gained traction in research circles but hasn't penetrated mainstream beekeeping practice, partly because propolis makes inspections significantly more difficult. Every frame cemented in place with propolis is a frame that takes more effort to pull, examine, and replace.

The colony's self-medication fights the beekeeper's workflow. The beekeeper scrapes off the immune system to get at the brood frames. Both sides are being rational. Neither side is winning.

The bees keep collecting resin. The beekeepers keep scraping it off. The propolis keeps showing up in antimicrobial research papers, in supplement bottles, in the residue on hive tools that no amount of rubbing alcohol will completely remove. It's been doing this since before the pyramids were built, and it shows no signs of stopping.