is a resinous mixture that honey bees collect from tree buds, sap flows, or other botanical sources. It is used as a sealant for unwanted open spaces in the hive. Propolis is used for small gaps (approximately 6 millimeters (0.2 in) or less), while larger spaces are usually filled with beeswax. Its color varies depending on its botanical source, the most common being dark brown. Propolis is sticky at and above room temperature (20° Celsius). At lower temperatures it becomes hard and very brittle.
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). Poplar resin is rich in flavonoids. "Typical" northern temperate propolis has approximately 50 constituents, primarily resins and vegetable balsams (50%), waxes (30%), essential oils (10%), and pollen (5%). 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, propolis contains viscidone, a terpene from Baccharis shrubs, and in Brazil, naphthoquinone epoxide has recently isolated from red propolis, and prenylated acids such as 4-hydroxy-3,5-diprenyl cinnamic acid have been documented. An analysis of propolis from Henan, China found sinapic acid, isoferulic acid, caffeic acid and chrysin, with the first three compounds demonstrating anti-bacterial properties. Also, Brazilian red propolis (largely derived from Dalbergia ecastaphyllum plant resin) has high relative percentages of the isoflavonoids 3-Hydroxy-8,9-dimethoxypterocarpan and medicarpin. Occasionally worker bees will even gather various caulking compounds of human manufacture, when the usual sources are more difficult to obtain. The properties of the propolis depend on the exact sources used by each individual hive; therefore any potential medicinal properties that may be present in one hive's propolis may be absent from another's, and the distributors of propolis products cannot control such factors. This may account for the many and varied claims regarding medicinal properties, and the difficulty in replicating previous scientific studies investigating these claims. Even propolis samples taken from within a single colony can vary, making controlled clinical tests difficult, and the results of any given study cannot be reliably extrapolated to propolis samples from other areas.
Propolis is marketed by health food stores as a traditional medicine, and for its claimed beneficial effect on human health.
Natural medicine practitioners use propolis for the relief of various conditions, including inflammations, viral diseases, ulcers, superficial burns or scalds.Propolis is also believed to promote heart health, strengthen the immune system and reduce the chances of cataracts. Old beekeepers recommend a piece of propolis kept in the mouth as a remedy for a sore throat. Propolis lozenges and tinctures can be bought in many countries. Though claims have been made for its use in treating allergies, propolis may cause severe allergic reactions if the user is sensitive to bees or bee products.
Some of these claims are being clinically investigated and several studies are published in the biomedical literature. Since the chemical composition of propolis varies depending on season, bee species and geographic location, caution must be applied in extrapolating results.