In studies on subjects, no significant effect on the percentages of growing and resting hairs was found after single application and prolonged exposure to both a selenium sulfide suspension and the same preparation without selenium sulfide.
ORENTREICH N, BERGER RA. Selenium Disulfide ShampooIts Influence on Hair Growth and the Follicular Cycle. Arch Dermatol. 1964;90(1):76-80. doi:10.1001/archderm.1964.01600010082017