**1. Introduction**

Propolis is formed by vegetable oils and resins, mixed with salivary secretions from bees, and may be in the form of isolated accumulations or combined with waxes. It is constituted by a complex mixture of various compounds and looks similar to a resinous wax collected by bees from tree shoots or other botanical sources. It is also used as glue to seal cracks or open spaces in the hive. Its color varies from green to brown and reddish, depending on its botanical origin and chemical composition. Bees can also use it to prevent diseases and parasites in the hive. In terms of chemical composition, it is generally composed of resin, wax, essential oils, phenolic acids, flavonoids, terpenes, aldehydes, alcohols, fatty acids, and phytosterols [1–4].

In this sense, propolis may represent a natural alternative in the search for bioactive compounds [5], since the use of secondary metabolites is increasing and represents a very broad field of research that can still be explored [6]. In addition, the wide variety of natural substances that can be found in organic matrices can provide key substances for the treatment of various pathologies [7]. The main substances present in propolis are low molecular weight, nonpolar, and volatile compounds [8].

The chemical composition of volatile substances present in propolis is very varied. Several compounds can be found, such as: nerolidol, α-pinene, β-pinene, cedrol, 3-methyl-2-buten-1-ol, octane, tricyclene, β-caryophyllene, spatulenol, δ-cadinene, selina-3,7(11)diene, nerolidol, benzenepropanoic acid, allyl benzyl ether, 1,8-epoxyp-menth-2-ene, γ-terpinene, mentha-3(8),6-diene, cis-sabinol, 2,3-dehydro-1,8-cineole, α-copaene, p-ethylguaiacol, β-copaene, junipene, γ-cadinene, (3e)-6-phenyl-3-hexen-2-one, p-mentha-1(7),2-dien-8-ol, 4-terpineol, β-fenchyl alcohol, sabinene, δ-3-carene, limonene, α-thujene, α-terpinene, α-terpinolene, trans-verbenol, camphene, verbenene, o-cymene, and α-phellandrene. Moreover, geographical origin and seasonality may influence this composition [9, 10].

Authors have been studying volatile compounds and their applications [11–13] and have seen how these secondary metabolites can be promising in treating various diseases, such as neurodegenerative syndromes [14, 15] and infections caused by microorganisms [16, 17]. Considering the importance of the search for volatile substances present in propolis that may be beneficial for the maintenance of human health, this work aims to perform a literature review in order to address the main biological activities of these metabolites.
