Evidence That Two Alkyl Ester Quaternary Ammonium Compounds Lack Substantial Human Skin-Sensitizing Potential

Ian R. Jowsey; Albert M. Kligman; Ian R. White; An Goossens; David A. Basketter


Dermatitis. 2007;18(1):32-39. 

In This Article

Abstract and Introduction


Background: Alkyl ester quaternary ammonium compounds (ester quats) are used extensively in fabric rinse conditioners. It is important to document in the literature the outcome of historical studies that were performed to assess the risk of adverse skin effects associated with their use.
Objectives: (1) To document the outcomes of historical studies performed to evaluate the skin sensitizing potential of two ester quats (the di-[hardened tallow fatty acid] ester of 2,3-dihydroxypropyl-trimethyl ammonium chloride [HEQ] and the dialkyl ester of triethanol ammonium methyl sulfate [TEA-Quat]) and (2) to demonstrate that these ester quats lack marked skin-sensitizing potential in humans, such that they do not present a risk of contact allergy for consumers who use fabric rinse conditioners.
Methods: Each material was assessed in the human maximization test in a panel of 25 volunteers. Diagnostic patch testing was also performed with each material in a population of 239 patients undergoing routine patch testing for suspected allergic contact dermatitis. These data are also considered in the context of an exposure-based quantitative risk assessment.
Results: Neither HEQ nor TEA-Quat was found to cause skin sensitization under the conditions of the human maximization test. No evidence of contact allergy to the materials was found among the relatively small population assessed by diagnostic patch testing.
Conclusions: This study provides evidence that HEQ and TEA-Quat lack substantial skin-sensitizing potential in humans. Taken together with similar data for other ester quats, it suggests that compounds in this class are unlikely to be significant human contact allergens.


Fabric conditioners are used at the rinse stage of the wash process, primarily to preserve the original soft feel of fabrics. Cationic surfactants are the principal active ingredients in these products. In particular, di-hardened tallow dimethyl ammonium chloride (DTDMAC) was used extensively for more than two decades in fabric conditioners.[1]However, because of environmental concerns associated with the poor biodegradability of DTDMAC,[2]there was a subsequent need to identify compounds that had more favorable environmental attributes but were capable of delivering comparable levels of efficacy.[1]Thus, over the last decade or so, DTDMAC has largely been replaced with alkyl ester quaternary ammonium compounds (ester quats),[1,2]which are quaternary ammonium compounds that contain one or (more often) two weak ester linkages. These weak ester linkages may underlie the improved biodegradability of the materials.[1]

Given the extensive use of fabric conditioners, it is essential to assess the potential for adverse effects to be associated with their use. This is particularly true in the case of adverse cutaneous effects such as skin sensitization because traces of the active ingredients may remain in the fabrics and thus come into prolonged contact with skin. The safety of fabric conditioner is supported by a number of studies. These studies include an assessment of the skin-sensitizing potential of formulations that contain dialkyl dimethyl ammonium sulfate (DADMAMS).[3]Also, Rodriguez and colleagues described the use of repeat insult patch testing to examine the skin-sensitizing potential of fabric conditioner formulations that contain dialkyl dimethyl ammonium chloride (DADMAC) or the ester quat diethyl ester dimethyl ammonium chloride (DEEDMAC).[4]These investigations indicated that formulations containing these active ingredients apparently lack skin-sensitizing potential in humans. Indeed, Rodriguez and colleagues confirmed that no evidence of skin sensitization was found after tests of more than 4,000 individuals over a 20-year period.[4]

We seek to publish historical data that were generated to assess the (human) skin-sensitizing potential of two other ester quats used extensively in fabric rinse conditioners: the dialkyl ester of triethanol ammonium methyl sulfate (TEA-Quat) and the di-(hardened tallow fatty acid) ester of 2,3-dihydroxypropyl-trimethyl ammonium chloride (HEQ). The structures of these and other ester quats are shown in Figure 1. Whereas published data demonstrate that both TEA-Quat and HEQ lack skin-sensitizing potential in predictive animal methods,[2]the data presented here represent the first published proactive assessment of the skin-sensitizing potential of these compounds in humans. We also consider these data in the context of an exposure-based quantitative risk assessment that has been used previously to provide insights into the risk of contact allergy associated with the use of fragrance materials,[5,6]preservatives,[7,8]and transition metals.[9]

Figure 1.

Chemical structures of selected ester quats. (DEEDMAC = diethyl ester dimethyl ammonium chloride; HEQ = di-(hardened tallow fatty acid) ester of 2,3-dihydroxypropyl-trimethyl ammonium chloride; TEA-Quat = dialkyl ester of triethanol ammonium methyl sulfate)


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