PROBLEM TO BE SOLVED: To provide means of essentially and efficiently preventing and/or improving white hair.SOLUTION: The present invention provides: a differentiation inhibitor of pigment stem cells in a hair follicle bulge and a white hair preventing and/or improving agent, which are characterized by containing CXCL12 (stromal cell-derived factor-1) as an active ingredient； and a method for evaluating hair whitening and a method for screening substances for preventing and/or improving white hair with an amount of CXCL12 expression as an index.SELECTED DRAWING: None【課題】白髪を根本的にかつ効率的に予防及び／又は改善する手段を提供すること。【解決手段】ＣＸＣＬ１２（ｓｔｒｏｍａｌ ｃｅｌｌ-ｄｅｒｉｖｅｄ ｆａｃｔｏｒ－１）を有効成分として含有することを特徴とする、毛包内バルジ領域の色素幹細胞の分化抑制剤、白髪の予防及び／又は改善剤、ならびにＣＸＣＬ１２の発現量を指標とした毛髪の白髪化の評価方法、白髪の予防及び／又は改善物質のスクリーニング方法。【選択図】なし
