18-Methyleicosanoic acid (18-MEA) is an unusual branched-chain fatty acid that is covalently bounded, possibly via a thioesteroresterlinkage, to the cuticle surface of hairfiber s. It is also known that the lipid layermakes the hairsur face hydrophobic and acts as a boundary lubricant to decrease friction resistance. 18-MEA can be easily removed; however, underalkaline conditions such as in the presence of hairbleach orper manent waving, the hairsur face becomes hydrophilic and the friction increases. The absence of 18-MEA may influence the sensory perception of hair, making it feel dried or hard to finger/comb through. We also found that exposure to ultraviolet (UV) radiation affects 18-MEA on hair surface using Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS). We therefore think it is important to study the damage to boundary lipids caused by the external stimuli in daily life. A technology for the deposition of a persistent hydrophobicity to bleached hair surfaces using 18-MEA is reviewed. It was found that the combination of 18-MEA with specific cationic surfactants system makes the bleached hair surface hydrophobic, and its hydrophobicity is maintained even after shampooing. Characterization of adsorbed layers on a mica surface was performed using Atomic Force Microscopy (AFM). The results revealed that system formed an uniform layer with high wear resistance.