Methods of protecting keratinous fibers from extrinsic damage and/or repairing keratinous fibers damaged by extrinsic conditions by applying to keratinous fibers a composition comprising at least one sugar chosen from C3 to C5 monosaccharides and derivatives of these monosaccharides. Extrinsic damage is damage that is caused by conditions such as sun, chemical damage, e.g., from detergents, bleaching, relaxing, dyeing, and permanent waving, and heat, e.g., from hair dryers or curlers. Examples of keratinous fiber include hair, eyelashes, and eyebrows.