Hair Damage 386 Conclusion Summing up, after leaving the follicle, hair is continuously damaged by any number of the environmental factors. The extent at which this process occurs is dependent on its history, with previous damages enhancing this process. There is also a dependence on the state by which hair receives its stresses, with wet fibers appearing more susceptible than dry. The attack of various external agents manifests in damage to disulphide bonds before other components of the fiber show deterioration. Often the overall effect is not immediately measurable, but amplifies over time. The only damaging pathway of hair which does not necessitate a chemical pathway involves mechanical erosion of the fiber cuticle, as during grooming. This may be seen as a material abraded by friction with the cuticle serving as a barrier against external agents, its consummation leads to an ever large harmful effect of environmental factors. References 1. CR Robbins, Chemical and Physical Behavior of Human Hair, 4th ed. Springer-Verlag: New York (2002). 2. RDB Fraser, TP MacRae, LG Sparrow and DAD Parry, Disulphide bonding in alpha- keratin, Int J Biol Macromol, 10 106-112 (1988). 3. TE Creighton, Disulphide bonds and protein stability, BioEssays 8(2) 57-63 (1988). 4. R Meredith, Rigidity, moisture and fiber structure, J Text Inst 48(6) T163-T174 (1957). 5. MK Denk, The variable strength of the sulfur–sulfur bond, Eur J Inorg Chem 10, 1358- 1368 (2009). 6. TM Florence, Degradation of protein disulphide bonds in dilute alkali, Biochem J 189(3) 507-520 (1980). 7. AS Nashef, DT Osuga, HS Lee, AI Ahmed, JR Whitaker and RE Feeney, Effects of alkali on proteins: disulfides and their products, J Agric Food Chem 25 (2) 245-251 (1977). 8. DB Volkin and AM Klibanov, Thermal destruction processes in proteins involving cystine residues, J Biol Chem 262(7) 2945-2950 (1987). 9. CE Reese and H Eyring, Mechanical properties and the structure of hair, Text Res J 20(11) 743-753 (1950). 10. A Kuzuhara, Analysis of structural changes in bleached keratin fibers (Black and White human hair) using raman spectroscopy, Biopolymers, 81, 506–514 (2006). 11. AJ Parker and N Kharasch, The scission of the sulfur-sulfur bond, Chem Rev, 59(4) 583- 628 (1959). 12. MA Manuszak, ET Borish and RR Wickett, The kinetics of disulfide bond reduction in hair by ammonium thioglycolate and dithiodiglycolic acid, J Soc Cosmet Chem, 47 49-58 (1996).