A method of promoting hair growth can include: a polypeptide having a sequence that has at least 75% complementarity to or at least 75% identical to SPR4; and topically administering the polypeptide to a subject. This can include putting or causing the polypeptide to be in the skin, such as in any dermal layer. In one aspect, the method can include administering the composition topically so as to administer the polypeptide to the subject. In one aspect, the method can include administering the polypeptide to skin of the subject. In one aspect, the method can include administering the polypeptide to a hair follicle of the subject. In one aspect, the method can include administering the polypeptide to a bald spot of the subject.