The present invention provides a new pharmaceutical application of a 15,15-difluoroprostaglandin F 2± derivative. As a result of intensive studies in order to find a new pharmaceutical application of a 15,15-difluoroprostaglandin F 2± derivative, it was found that, in a European Phase III clinical, trial for tafluprost, one of the 15,15-difluoroprostaglandin F 2± derivatives, with patients with open-angle glaucoma or ocular hypertension, tafluprost has actions of growing eyelashes, making eyelashes thicker, and changing the color thereof, that is, has an effect of promoting the growth of hair (eyelashes). Therefore, a 15, 15-difluoroprostaglandin F 2± derivative is useful as a hair growth promoting agent, and is expected to be useful as an active ingredient of a preventive or therapeutic agent for a disease associated with hair such as alopecia and a hair care product or a hair cosmetic product for regrowing hair, growing hair, increasing hair density, nourishing hair, or the like.
