Allergic Contact Dermatitis from Propolis

Susan E. Walgrave; Erin M. Warshaw; Lynn A. Glesne


Dermatitis. 2005;16(4):209-215. 

In This Article

Responsible Allergens

The main allergens found in propolis are 3-methyl-2-butenyl caffeate and phenylethyl caffeate, both of which are constituents of LB-1 (fig1 and Table 1 ).[9,10] LB-1 was the first allergen identified in propolis.[2] Chemical separation of different propolis samples and poplar bud extracts reveals that LB-1 is always present.[11] LB-1 was originally thought to consist solely of 1,1-dimethylallyl caffeic acid ester[11,12] but more recently has been found to consist mainly (87%) of three isomeric pentenyl caffeates.[10] 3-Methyl-2-butenyl caffeate, the main component of LB-1, has been identified as the strongest sensitizer;[9,10] 2-methyl-2-butenyl caffeate and 3-methyl-3-butenyl caffeate are the other two pentenyl caffeates (pentenyl caffeates make up 87% of LB-1). Phenylethyl caffeate is a smaller component (7.9%) of LB-1 and elicits strong reactions in patients known to be sensitive to propolis.[10] In general, esters of caffeic acid play an important role in sensitization. In one study, all caffeates tested showed a moderate to strong sensitizing capacity.[9] Propolis is generally rich in these caffeates when bees have the opportunity to collect the sticky bud exudates of poplar species.[13–20]

Structure of propolis allergens.

Benzyl salicylate and benzyl cinnamate (see fig1 and Table 1 ) are less frequent sensitizers.[9,10] In guinea pigs, benzyl salicylate is a moderate sensitizer[10,21] whereas benzyl cinnamate is a very weak[10] to moderate[21] sensitizer. Hausen and colleagues patch-tested three propolis-allergic patients; none reacted to either benzyl salicylate or benzyl cinnamate.[10] In Europe and Japan, benzyl salicylate has been found to be a frequent sensitizer in cosmetic-sensitive patients[22–27] whereas other studies have found fewer reactions from benzyl salicylate in similar patients.[28,29] Regardless, propolis-sensitive patients should be counseled about potential cross-reactions to cosmetics or products containing benzyl salicylate and benzyl cinnamate.

When studied experimentally, flavonoids have generally shown a weak capability or no capability for sensitization.[30] Other compounds found in propolis include waxes (mostly beeswax) and fatty acids, essential oils, pollen, and other organics and minerals.[2,5] None of these constituents have been found to be the responsible contact allergen.[2,31–33]