1.  Field of the Invention
The present invention relates to a method for screening an ingredient which is to be applied to the hair; a kit for carrying out the screening; and a composition comprising an ingredient exhibiting effects to accelerate absorption of an active ingredient through skin pores (hereinafter the absorption will be referred to as “skin-pore absorption”) and transfer of the active ingredient to sebum, the effects being confirmed by means of the screening method. 
2.  Background Art
An important step in the development of a hair-growing agent is to confirm that an active ingredient exhibits excellent hair-growing effect and has penetrability so as to reliably reach a target site.  Whether or not the active ingredient reliably reaches the target site greatly depends on the properties of the active ingredient or the base ingredient of the hair-growing agent. 
The mechanism of absorption of a drug or an active agent through hair follicles has become of interest, since hair follicles are considered to be an effective route through which a hair-growing agent as well as a vaccine or a gene can be administered. 
The degree of transfer of a drug to sebum (hereinafter the degree will be referred to as “sebum transferability”) has been reported to influence whether the drug easily reaches a target site in the skin (e.g., hair follicles or sebaceous gland) (Critical Reviews, 14 (3): 207 219 (1997)). 
The penetrability of a drug through the hair follicles has been studied, for example, by the following methods:
(1) a method for observing tissue sections by means of fluorescence labeling or radioisotopes (Suzuki, M., et al.,  J. Soc.  Cosmet.  Chem. ( 1978), Nicholau, G., et al.,  Xenobiolica (1987), Lieb, L. M., et al.,  J. Invest.  Dermatol. ( 1995)) and
(2) a method for comparing hairy skin and hairless skin with respect to the transdermal permeability of a drug (e.g., comparison of hairless rat and hairy rat: Illel, B., et al.,  J. Pherm.  Sci. ( 1991); comparison of normal human skin and skin which has received burns and has subsequently healed: Hueber, F., et al.,  J. skin Pharmacologic. ( 1994)). 
However, method (1) is qualitative rather than quantitative, and the method involves the time-consuming preparation of tissue sections.  In method (2), absorption of a drug is studied only from the viewpoint of transdermal absorption, and “skin-pore absorption” and “sebum transferability,” which are important properties of a hair-growing agent, cannot be confirmed directly. 
Therefore, the aforementioned conventional methods encounter difficulty in directly confirming that a drug reaches a target site in the skin and exerts the intended effects.