Abstract

Surfactants, an important component of cleansers, often cause itch in humans. Topical application of sodium laurate and N-lauroylsarcosine sodium salt to the skin of mice immediately (for 1–1.5 hours) increased scratching, and the former increased scratching again between 2 and 3 hours after application. Thus, we examined the mechanisms of sodium laurate–induced delayed scratching. Sodium laurate (0.1%–10%) increased delayed scratching and skin surface pH in a concentration-dependent manner. N-lauroylsarcosine sodium salt had no effect on these parameters, and sodium hydroxide solution did not increase delayed scratching. Sodium laurate–induced delayed scratching was markedly inhibited by the H₁ histamine receptor antagonist terfenadine, but it was not affected by mast cell deficiency. Sodium laurate application had no effect on the number of total and degranulated mast cells, and did not induce plasma extravasation or the infiltration of inflammatory cells in the skin. Sodium laurate application increased the histamine content of the epidermis, but not that of the dermis, in normal and mast cell–deficient mice. Sodium laurate application increased the ratio of 53-kDa l-histidine decarboxylase (HDC, a key enzyme for histamine production) to 74-kDa HDC in the mouse epidermis and in a human keratinocyte culture. Sodium laurate increased histamine in the human keratinocyte culture, without affecting cell viability. The present results suggest that sodium laurate induced delayed scratching at an alkaline pH through the increased production of histamine in keratinocytes, which may be due to enhanced processing of 74-kDa to 53-kDa HDC.