Consideration of the World’s First Approach for Preventing Irritation by Reducing the Amount of Surfactant Adsorption to Proteins

Abstract

Itching is a typical problem of the scalp. In the past, numerous studies have been reported on skin irritation and adsorption by surfactants included in shampoo formulations. However, only few studies have examined the adsorption of surfactants to the stratum corneum in terms of physical properties such as ionic properties. Moreover critical micelle concentration (CMC) has not yet been comprehensively investigated. In this study, we defined the adsorption index as “anionicity of anionic surfactant at skin pH × CMC of detergent” in order to reduce the amount of surfactant adsorption on the stratum corneum. We investigated the relation between the absorption index and the absorption of anionic surfactants on the stratum corneum and found it to be a useful index. We tried to use sodium lauraminopropionate (LAP), a type of amphoteric surfactant, focusing on reducing the molecular occupied area as a method to lower the adsorption index. We found that LAP effectively lowered CMC and also reduced skin irritation compared to Cocamidepropyl Betaine (CAPB), a general-purpose amphoteric surfactant. These results suggest that reducing the amount of adsorbed anionic surfactants in the stratum corneum suppresses barrier disruption and consequently alleviates skin irritation. This study should contribute to the development of safe cosmetics.