To provide a hair growth inhibitor capable of inhibiting growth or elongation of the hair and having high safety, and to provide a preparation for external use, such as a pharmaceutical, quasi-drug product, and cosmetic, containing the inhibitor.

This hair growth inhibitor contains one or more methyl isopropyl phenols, such as thymol(5-methyl-2-isopropylphenol), carvacrol(2- methyl-5-isopropylphenol), and biosol (3-methyl-4-isopropylphenol), as active ingredients. Various compositions used for the preparation for external use, such as the cosmetic, are prepared by mixing the active ingredients with aqueous-phase components and oil-phase components through ordinary procedures.