Causes of hair loss have not been completely clarified and still remain unknown in many points. However, it appears that hair loss is partly caused by a mechanism wherein androgenic hormones in the scalp become active via the activation of DHT hormone by 5α-reductase and thus the activity of cells in hair roots is lost. In the present invention, an antibody, said antibody being obtained by inoculating a female bird with 5α-reductase or DHT as an antigen, is administered to the scalp so that the activity of DHT is suppressed and the activity of cells in hair roots is elevated. This antibody can be used in the form of a composition together with other component(s), for example, as a hair tonic together with another hair growth promoter.