Propolis is a resinous mixture that honey bees collect from tree buds, sap flows or other plant sources. It is used as a sealant to coat the inner walls of their hives in order to keep their hives sterile and free from bacteria. People began using propolis more than 2,300 years ago for many purposes, the foremost of which was applying it to wounds to fight infection. Studies have found propolis to be active against a variety of microorganisms, including bacteria, viruses and protozoans. Propolis is a subject of recent dentistry research since there is some evidence that propolis may actively protect against dental caries and other forms of oral disease due to its anti-microbial properties. Propolis has also been reported to be effective in treating the inflammatory component of skin burns. It has immunomodulatory effects by exhibiting both immunosuppressive and immunostimulant activities.