Soluble keratin derivatives are disclosed. The soluble keratin derivatives may include a soluble keratin protein having at least one substituted chemical group at a lysine group, terminal amine group and/or hydroxyl amino acid group of a soluble keratin protein. Soluble keratin derivatives may be formed by succinylation or quaternisation, or by reaction with fatty acid derivatives. The soluble keratin derivatives may be used in personal care formulations, and may also comprise mixtures of several different soluble keratin derivatives.