In addition to covalently attached 18-MEA on the epicuticle surface, free fatty acids have also been found to reside on the surface . The resulting hydrophobic coating of the hair cuticle acts as a boundary lubricant and overall protective layer . Experimental techniques, including X-ray photoelectron spectroscopy (XPS), have been used along with electron microscopy and mass spectroscopy techniques to study the composition of the hair surface and its degradation . One of the key findings of these studies is the reduction of 18-MEA content along the fiber from root to tip. Additionally, chemical and physical damage to hair fibers results in a decreased number of covalently bound 18-MEA in the epicuticle. Chemical treatment of hair to remove 18-MEA increases hydrophilic surface patches. Korte et al. demonstrated bleaching of hair fibers results in removal of the top hydrophobic layer via cysteine oxidation by measuring sulfate surface density with atomic force microscopy . The chemically treated "damaged" hair surface contained clusters of cysteic acid with a quasi-ordered structure. Weiand et al. built a coarse grained 18-MEA surface model, using graphene, incorporating different amounts of cysteic acids randomly distributed to study the effects of damage on wetting phenomena of the hair surface . Reducing the hydrophobicity of the surface resulted in increased wetting of the model surface, and the authors were able to compare directly to contact angle experiments. A detailed molecular view of the hair surface and its composition has become an area of intense interest, particularly for development and refinement of cosmetic formulations. For a more comprehensive review of the physicochemical properties of the hair surface, the authors refer the reader to and .