PROBLEM TO BE SOLVED: To provide an involucrin expression promotor which promotes the expression of involucrin, and to provide a horny layer formation promoter, a humectant, a hair waving agent and a skin external preparation.SOLUTION: The involucrin expression promoter horny layer formation promoter humectant, hair waving agent and skin external preparation include one or more kinds of plants selected from Gomphandra tokinensis Gaertn., Eurya japonica Thunb., Iresine herbstii, Eleocharis kuroguwai Ohwi, Gymnema tingens (Roab.) Spreng., Derris balansae Gagnep. and Diploclisia glaucescens (Blume) Diels. or the extract(s) thereof as an active ingredient(s).