Propolis 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, 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 (20º 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-eiprenyl cinnamic acid have been documented. An analysis of propolis from Henan, China found sinapinic 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-eimethoxypterocarpan and medicarpin.