MEA, diethanolamine (DEA), and triethanolamine (TEA) serve as rust preventive agents with emulsifying properties in wb MWF. In several recent studies, MEA ranked first among the MWF allergens. The use of DEA in wb MWF has declined since the mid-1990s, due to a potential formation of carcinogenic N-nitrosamines. This led to a far lower frequency of sensitization to DEA compared to MEA. TEA is a rare MWF allergen. It is not only used in MWF, but also a frequent component of creams and cosmetics [5, 6, 8, 14].

The main sensitizers in colophonium are oxidation products of abietic acid and other resin acids. The same allergens are found in distilled tall oil (DTO), which is a base material of wb MWF. About 30 % of the DTO are resin acids, and of these, about one-third is abietic acid. Resin acids oxidise rather quickly on exposure to air, which occurs on a large scale during normal use of wb MWF [7, 11]. In this way, the used wb MWF at the workplace contains the same allergens as the colophony or abietic acid patch test preparations. A relevant exposure to these allergens is given, even though their concentration in the MWF may be rather low, because the MWF dries up on the contaminated, mostly pre-damaged skin [12]. Epidemiological data confirmed the high risk of sensitization to colophonium in metalworkers with OCD and exposure to wb MWF [4].