Compositions, optionally heat-activated, methods and kits for protecting keratinous fibers from extrinsic damage or repairing keratinous fibers damaged by extrinsic conditions by applying to keratinous fibers a composition comprising at least one compound chosen from C.sub.3 to C.sub.5 monosaccharides substituted with at least one C.sub.1 to C.sub.22 carbon chain, and heating the keratinous fibers.