Many excipients and emulsifiers are common ingredients to topical pharmaceutical and cosmetic products, the former being likely to induce sensitization. Typical examples are wool alcohols, fatty alcohols (e.g., cetyl alcohol), and propylene glycol . They may also be sensitizing in cosmetics, as is the case with maleated soybean oil . Emulsifiers in particular have long been regarded as irritants, but their sensitization capacities should not be overlooked. It is imperative, of course, that patch testing be properly performed to avoid irritancy and that the relevance of the positive reactions be determined. This is certainly the case for cocamidopropylbetaine, an amphoteric tenside mainly present in hair-and skin-cleansing products. Whether the compound itself or cocamidopropyl dimeth-ylamine, an amido-amine, or dimethylaminopropylamine (both intermediates from the synthesis) are the actual sensitizers is still a matter of discussion [45,46]. It is also not clear whether cocamidopropyl-PG-dimonium chloride phosphate (phospholipid PTC) , a new allergen in skincare products, can cross-react with cocamidopropylbetaine.
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