REPAIR works to strengthen and keep the hair you already have. This serum is formulated with 2 potent peptide combinations, GHK-Cu and Zn-Thymulin to help strengthen, thicken, and retain existing hair follicles. In studies, GHK-Cu has been shown to strengthen existing hair by stimulating growth in areas that are lacking thickness. Zn-Thymulin is a combination of Zinc and a nonapeptide called Thymulin. Together, Zn-Thymulin has been shown to extend the anagen phase of hair follicles and reduce hair loss associated with a zinc deficiency.