Volume 50, Issue 7 pp. 888-894
ORIGINAL ARTICLE

Sensory irritation to methylparaben is caused by its low metabolism in the skin

Rie Ninomiya

Rie Ninomiya

Safety Science Research Laboratories, Kao Corporation, Odawara, Japan

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Takafumi Nishijima

Corresponding Author

Takafumi Nishijima

Safety Science Research Laboratories, Kao Corporation, Odawara, Japan

Correspondence

Takafumi Nishijima, Safety Science Research Laboratories, Kao Corporation, Kotobuki-cho 5-3-28, Odawara, Kanagawa 250-0002, Japan.

Email: [email protected]

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Masahiro Aoshima

Masahiro Aoshima

Department of Dermatology, Hamamatsu University School of Medicine, Hamamatsu, Japan

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Hitoshi Sakaguchi

Hitoshi Sakaguchi

Safety Science Research Laboratories, Kao Corporation, Odawara, Japan

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Yoshiki Tokura

Yoshiki Tokura

Department of Dermatology, Hamamatsu University School of Medicine, Hamamatsu, Japan

Allergic Disease Research Center and Department of Dermatology & Skin Oncology, Chutoen General Medical Center, Kakegawa, Japan

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First published: 22 March 2023

Abstract

Sensitive skin is a well- known skin condition showing sensory irritation to daily used products such as cosmetics or pharmaceuticals, possibly containing sensory irritants. Methylparaben (MP), widely used as a preservative, is a representative sensory irritant and hydrolyzed in the skin. We aimed to clarify the relationship between MP sensory irritation and MP hydrolysis. First, we investigated the percutaneous penetration and hydrolysis of MP by using an ex vivo pig skin system and confirmed that topically applied MP was immediately hydrolyzed to p-hydroxybenzoic acid (PHBA). We next evaluated whether MP or PHBA causes sensory irritation using a well-used stinging test in human skin and found that MP, but not PHBA, induced irritation. Additionally, MP, but not PHBA, increased intracellular calcium in cultured TRPA1-expressed HEK293 cells, supporting the stimulatory activity of MP. Five and 10 individuals with sensitive and non-sensitive skin, respectively, were selected by a questionnaire and stinging test. In their biopsied skin samples, MP hydrolytic activity was significantly lower in sensitive than non-sensitive skin. Finally, we examined the activity of carboxylesterase (CES), which promptly hydrolyzes MP to PHBA. By using specific inhibitors of CES and CES2, we found that CES1 was responsible for MP metabolism. Our study suggests that low skin metabolism of topical agents is one of the causes of skin sensory irritation and resultant sensitive skin.

CONFLICT OF INTEREST STATEMENT

None declared.

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