J Pharm Bioallied Sci, 2011 Oct;3(4):479-95
Propolis is a resinous substance produced by honeybees as defense against intruders. It has relevant therapeutic properties that have been used since ancient times. Nowadays, propolis is of increasing importance as a therapeutic, alone or included in many medicines and homeopathic products or in cosmetics. Propolis is produced worldwide and honeybees use the flora surrounding their beehives for its production. Therefore its chemical composition may change according to the flora. The phenolic and volatile fractions of propolis have been revised in the present study, as well as some of the biological properties attributed to this natural product. An alert is given about the need to standardize this product, with quality control. This has already been initiated by some authors, mainly in the propolis from the poplar-type. Only this product can constitute a good complementary and alternative medicine under internationally acceptable quality control…
Propolis is a heterogeneous product constituted by several groups of compounds. Moreover, the chemical composition depends strongly on the phytogeographic characteristics of the collection site, as honey bees can only use the plant species existing in their habitats. Their chemical variability can give rise to diverse types of biological activities or diverse structures may present similar properties. Therefore, to make a standardization and quality control of this product is very difficult, particularly if we take into account the quantification of the active substances. Popova et al.  have proposed to specify multiple standards for different propolis types according to their plant source and corresponding chemical profile. Popova et al.  has already made a standardization for the poplar-type propolis from Europe, Asia, and Americas. More recently, Popova et al.  have validated a spectrophotometric method for the quantification of prenylated flavanones in the 'Pacific' propolis from Taiwan. In addition, it is necessary to connect a particular chemical propolis type to a specific type of biological activity for formulating recommendations for the practitioners. Only by following this scheme will it be possible for people to choose and make more efficient use of the beneficial properties of propolis, in respect to complementary and alternative medicine. 
In spite of propolis being commonly used in cosmetic and medicinal preparations owing to its antiseptic, anti-inflammatory, and anesthesic properties, it is not completely innocuous because 1.2 to 6.6 patients who were patch-tested for dermatitis were sensitive to propolis. The main allergens were 3-methyl-2-butenyl caffeate and phenylethyl caffeate, that is, components present in the poplar-type propolis.  Clinical allergy in humans is presented as contact dermatitis or oral mucositis, beekeepers being the most affected. Nevertheless there has been a recent rise in this incidence among biocosmetic users, on account of the increasing popularity of natural products such as propolis.  According to these authors, patients with an allergy to propolis may be at risk of cross-sensitization with balsam of Peru, a common allergen found in flavoring agents, perfumed products, certain spices, and products that contain the peel of citrus fruit.
Therefore, propolis is a complex natural product with a great diversity of chemical structures and subsequent biological activities, nevertheless, it is not completely innocuous and care must been taken, mainly when such a product has a great diversity of origins. An absence of quality control may be pernicious to human health.