Propolis

Propolis, produced by the western honey bee (Apis mellifera)
Two bars from a top bar hive that the bees have glued together using propolis. Separating the bars will take notable effort as the propolis has hardened.
Propolis on the upper bar

Propolis or bee glue is a resinous mixture that honey bees produce by mixing saliva and beeswax with exudate gathered from tree buds, sap flows, or other botanical sources. It is used as a sealant for unwanted open spaces in the beehive. Propolis is used for small gaps (around 6 mm (1⁄4 in) or less), while gaps larger than the bee space (around 9 mm (3⁄8 in)) are usually filled with burr comb. Its color varies depending on its botanical source, with dark brown as the most common. Propolis is sticky above 19 °C (66 °F), while at lower temperatures, it becomes hard and brittle.

When foraging, worker bees primarily harvest pollen and nectar, while also collecting water and plant resin necessary for the production of propolis. The chemical composition and nature of propolis depend on environmental conditions and harvested resources.

Types

Propolis types are distinguished by their botanical sources and chemical profiles. Poplar-type propolis is common in temperate regions, including Europe, North America and western Asia. Brazilian green propolis is derived principally from Baccharis dracunculifolia, while Dalbergia ecastaphyllum is a major resin source for Brazilian red propolis. Other recognized types include birch, Mediterranean and Pacific propolis.

Purpose

Propolis drops in red (units in micrometers)

Bees seal the beehive with propolis to protect the colony from the elements, such as rain and cold winter drafts.

Propolis functions may include:[better source needed]

  1. Reinforcing the structural stability and reduce vibration
  2. Providing improved thermal insulation to the hive and reduce water loss
  3. Make the hive more defensible against parasites and predators by narrowing the existing entrance (in wild colonies) to a single "choke point"
  4. Mitigate putrefaction within the hive - bees usually carry waste out of and away from the hive, but if a small lizard or mouse, for example, finds its way into the hive and dies there, bees may be unable to carry it out through the hive entrance. In that case, they would attempt instead to seal the carcass in propolis, essentially mummifying it and making it odorless and harmless.

Honey bees also line the interior of their nests with a propolis envelope. This contributes to social immunity, the collective defenses that help protect a colony against pathogens and parasites.

Composition

Propolis in hive

The composition of propolis varies from hive to hive, from district to district, and from season to season. Normally, it is dark brown in color, but it can be found in green, red, black, and white hues, depending on the sources of resin found in the particular hive area. Honey bees are opportunists, gathering what they need from available sources, and detailed analyses show that the chemical composition of propolis varies considerably from region to region, along with the vegetation. In northern temperate climates, for example, bees collect resins from trees, such as poplars and conifers (the biological role of resin in trees is to seal wounds and defend against bacteria, fungi, and insects). Propolis contains plant resins, beeswax, pollen and volatile compounds, in proportions that vary between samples. Hundreds of chemical constituents have been identified across different types of propolis, including flavonoids, phenolic acids and their esters, and terpenoids. Commonly quoted fixed percentages of resin, wax, pollen and essential oils have been criticized as unsubstantiated. An analysis of propolis from Henan, China, found sinapinic acid, isoferulic acid, caffeic acid, and chrysin.

In neotropical regions, in addition to a large variety of trees, bees may also gather resin from flowers in the genera Clusia and Dalechampia, which are the only known plant genera that produce floral resins to attract pollinators. Clusia resin contains polyprenylated benzophenones. In some areas of Chile and Argentina Andean valleys, propolis contains viscidone, a terpene from Baccharis shrubs, and prenylated acids, such as 4-hydroxy-3,5-diprenyl cinnamic acid.

Overall, flavonoids, phenolic acids, and phenolic aldehydes are common constituents, while coumarins, stilbenes, and lignans are less common.

Uses

Traditional medicine and clinical research

Propolis has been used in traditional medicine and investigated in clinical studies, but evidence of therapeutic benefit remains limited. Differences in the composition of propolis preparations complicate comparisons between studies.

A 2026 systematic review of 45 randomized clinical trials found that propolis-containing preparations may reduce dental plaque and oral microbial counts, but rated the certainty of the evidence as very low. Direct evidence that these preparations prevent dental caries was insufficient.

Propolis preparations have also been studied for oral mucositis associated with cancer treatment. A 2026 review reported possible benefits, while identifying small sample sizes, problems with blinding, and differences in formulations as limitations of the evidence.

A 2026 meta-analysis of 20 randomized trials in adults with metabolic risk factors found reductions in fasting blood glucose and triglyceride levels, but no statistically significant effects on blood pressure, waist circumference or HDL cholesterol. The authors highlighted limited standardization of the preparations, heterogeneity in some outcomes and the need to establish long-term effects.

Musical instruments

Propolis is used by some string-instrument makers (violin, viola, cello, and bass) as a varnish ingredient. A tincture of propolis may be used to seal the surface of newly made violin family bridges, and may be used in the maintenance of the bores of pan flute tubes.[citation needed] Claims that Antonio Stradivari used propolis in the varnish of his instruments were disproven in 2009.

Adverse effects

Propolis can cause allergic contact dermatitis. Reported reactions to topical propolis products include cheilitis, lip swelling and inflammation of the surrounding skin.

References

  1. 1 2 Simone-Finstrom M, Spivak M (May–June 2010). "Propolis and bee health: The natural history and significance of resin use by honey bees". Apidologie. 41 (3): 295–311. doi:10.1051/apido/2010016. hdl:11299/182451.
  2. ↑ Ferreira JM, Fernandes-Silva CC, Salatino A, Negri G, Message D (August 2017). "New propolis type from north-east Brazil: chemical composition, antioxidant activity and botanical origin". Journal of the Science of Food and Agriculture. 97 (11): 3552–3558. Bibcode:2017JSFA...97.3552F. doi:10.1002/jsfa.8210. PMID 28078783.
  3. ↑ Kasote, Deepak; Bankova, Vassya; Viljoen, Alvaro M. (2022). "Propolis: chemical diversity and challenges in quality control". Phytochemistry Reviews. 21 (6): 1887–1911. Bibcode:2022PChRv..21.1887K. doi:10.1007/s11101-022-09816-1. PMC 9128321. PMID 35645656.
  4. ↑ Shanahan M, Simone-Finstrom M, Tokarz P, Rinkevich F, Read QD, Spivak M (2024). "Thinking inside the box: Restoring the propolis envelope facilitates honey bee social immunity". PLOS ONE. 19 (1) e0291744. Bibcode:2024PLoSO..1991744S. doi:10.1371/journal.pone.0291744. PMC 10830010. PMID 38295039.
  5. ↑ Toreti VC, Sato HH, Pastore GM, Park YK (2013). "Recent progress of propolis for its biological and chemical compositions and its botanical origin". Evidence-Based Complementary and Alternative Medicine. 2013 697390. doi:10.1155/2013/697390. PMC 3657397. PMID 23737843.
  6. ↑ Kasote, Deepak; Bankova, Vassya; Viljoen, Alvaro M. (2022). "Propolis: chemical diversity and challenges in quality control". Phytochemistry Reviews. 21 (6): 1887–1911. Bibcode:2022PChRv..21.1887K. doi:10.1007/s11101-022-09816-1. PMC 9128321. PMID 35645656.
  7. ↑ Salatino, Antonio; Salatino, Maria Luiza Faria (2021). "Scientific note: often quoted, but not factual data about propolis composition". Apidologie. 52 (2): 312–314. doi:10.1007/s13592-020-00821-x.
  8. ↑ Qiao Z, Chen R (August 1991). "[Isolation and identification of antibiotic constituents of propolis from Henan]". Zhongguo Zhong Yao Za Zhi = Zhongguo Zhongyao Zazhi = China Journal of Chinese Materia Medica (in Chinese). 16 (8): 481–2, 512. PMID 1804186.
  9. ↑ Mesquita RC, Franciscon CH (June 1995). "Flower visitors of Clusia nemorosa G. F. W. Meyer (Clusiaceae) in an Amazonian white-sand Campina". Biotropica. 27 (2): 254–8. Bibcode:1995Biotr..27..254D. doi:10.2307/2389002. JSTOR 2389002.
  10. ↑ Tomás-Barberán FA, García-Viguera C, Vit-Oliviera P, Ferreres F, Tomás-Lorente F (3 August 1993). "Phytochemical evidence for the botanical origin of tropical propolis from Venezuela". Phytochemistry. 34 (1): 191–6. Bibcode:1993PChem..34..191T. doi:10.1016/S0031-9422(00)90804-5.
  11. ↑ Armbruster WS (September 1984). "The Role of Resin in Angiosperm Pollination: Ecological and Chemical Considerations". American Journal of Botany. 71 (8): 1149–60. doi:10.2307/2443391. JSTOR 2443391.
  12. ↑ Bankova V (March 2005). "Recent trends and important developments in propolis research". Evidence-Based Complementary and Alternative Medicine. 2 (1): 29–32. doi:10.1093/ecam/neh059. PMC 1062152. PMID 15841275.
  13. ↑ Montenegro G, Mujica AM, Peña RC, Gómez M, Serey I, Timmermann BN (2004). "Similitude pattern and botanical origin of the Chilean propolis". Phyton. 73: 145–154. ISSN 1851-5657. Archived from the original on 17 December 2014. Retrieved 7 November 2008.
  14. ↑ Park YK, Alencar SM, Aguiar CL (April 2002). "Botanical origin and chemical composition of Brazilian propolis". Journal of Agricultural and Food Chemistry. 50 (9): 2502–2506. Bibcode:2002JAFC...50.2502P. doi:10.1021/jf011432b. PMID 11958612.
  15. ↑ Berenbaum MR, Calla B (January 2021). "Honey as a Functional Food for Apis mellifera". Annual Review of Entomology. 66 (1). Annual Reviews: 185–208. Bibcode:2021AREnt..66..185B. doi:10.1146/annurev-ento-040320-074933. PMID 32806934. S2CID 221165130.
  16. ↑ "Propolis". Memorial Sloan Kettering Cancer Center. Retrieved 19 October 2026.
  17. 1 2 Berto, Luciana Pisenti; Wierichs, Richard Johannes; Sakae, Letícia Oba; Niemeyer, Samira Helena; Carvalho, Thiago Saads (2026). "Propolis-containing formulations in caries prevention – a systematic review and meta-analysis". Clinical Oral Investigations. 30 (9) 388. doi:10.1007/s00784-026-07065-6. PMC 13473232. PMID 42593545.
  18. ↑ Assis, Matheus de Morais; Pino, Barbara Hana Silva Morales; Maquedano, Larissa Kaori; Carvalho, Felipe Gustavo; Marson, Fernando Augusto Lima; Longato, Giovanna Barbarini (2026). "Clinical Evidence on the Use of Propolis for Oral Mucositis". Pharmaceuticals. 19 (3): 425. doi:10.3390/ph19030425. PMC 13029452. PMID 41901272.
  19. ↑ Safia Obaidur Rab; Mudher Kadhem; Malathi H; Swati Mishra; Ishant Arora; Mehran Nouri (2026). "Propolis Supplementation and Metabolic Syndrome Components in Adults at Risk: A Systematic Review and Meta-Analysis of Randomized Controlled Trials". Health Science Reports. 9 (3) e71909. doi:10.1002/hsr2.71909. PMC 12935762. PMID 41767366.
  20. ↑ Fulton W (July 1997). "PROPOLIS SOAP – Used as a Ground for Violin Varnish". Southern California Association of Violin Makers. Retrieved 6 December 2020.
  21. ↑ "Stradivarius varnish myth debunked". BBC Music. 8 December 2009.
  22. ↑ "Secret behind the composition of the varnish on Stradivari violins revealed". PhysOrg.com. 4 December 2009.
  23. ↑ de Groot, Anton; Rustemeyer, Thomas (2026). "Contact Allergy to Propolis: Update 2013–2025". Dermatitis. 37 (4): 563–588. doi:10.1177/17103568251392243. PMID 41346028.
  24. ↑ "Propolis". Memorial Sloan Kettering Cancer Center. Retrieved 19 October 2026.