160 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Virgin hair, when immersed in formic acid, swelled diametrally approximately 35•o above the diameter of the dry fibre. Cosmetically-altered hair samples swelled to different amounts. Some fibres swelled the same as or only a little more than virgin hair, approximately 35-405/o above the diameter of dry fibres. Other fibres were observed to swell to over 100•o more than their dry diameter, indi- cating (9) an approximate 50•o loss of disulphide cross-link content. Miyazawa et al. (8) have also observed similar reductions in the cross-link content of cosmetically-altered hair. As a general observation, it was noticed that the fibres displaying greatest diametral swelling in formic acid also displayed the greatest tendency to split. No direct correlation was obtained between diametral swelling in formic acid and degree of splitting because it appears that the degree of splitting depends upon grooming conditions as well as disulphide bond content, and therefore no direct correlation could be expected to exist. It was also noticed that persons with hair that swelled more in formic acid were less satisfied with the appearance and condition of their hair. It seems likely that the cross-link content of the hair is at least partially responsible for the condition and manageability of the hair. That is, a reduction of the cross-link content of the hair, which may be introduced by some cosmetic treatments, results in a reduction of the ability of fibres to with- stand the abrasive forces normally associated with hair grooming, causing an increase in hair damage during grooming, and appears to result in a loss of manageability of the hair. DISCUSSION The results presented above indicate that the structural changes observed in hair fibres can be due entirely to the mechanical abrasion associated with normal hair grooming. This study has demonstrated that shampooing of virgin hair is sufficient in itself to damage and completely remove the cuticle. it is, of course, probable that some other treatments may also produce the same effect, but these have not yet been exhaustively investigated. It also appears that brushing of the hair contributes to damage to the cortex, and is at least partially responsible for the production of split ends in hair. No attempt has yet been made to determine the relative roles played by all of the hair grooming processes in breakdown of hair fibres. Some cosmetically-altered hair is more prone to mechanical breakdown during grooming than virgin hair. This hair exhibits a greater tendency to swell in formic acid, indicating a loss of cross-link content resulting from the cosmetic treatment. It appears that the cosmetic treatment has reduced the cross-link content of the hair and that this has rendered the hair less able to withstand the mechanical abrasion associated with hair grooming, resulting in earlier splitting of the fibres.

A STUDY OF DAMAGED HAIR 161 Hydrogen bonds represent another useful form of cross-linking. Hydrogen bonds are reversibly broken every time hair is wet and are reformed again when it dries. Because of the decrease in hydrogen bonding, wet hair is completely unmanageable. Observations made during this study have indicated that wet hair is far more susceptible to damage during grooming than dry hair, and it would thus appear that minimal handling and brushing of wet hair could reduce the extent of physical damage to the hair. CONCLUSION This study has shown that the mechanical deterioration of hair which results in the production of split ends can be entirely attributable to the abrasion associated with hair grooming. It has also indicated that the increased tendency of hair to split after cosmetic treatments, particularly perming and bleaching, appears to be due to a reduction in the cross-link content of the fibres. To prevent this mechanical damage minimum brushing and shampooing would appear to be desirable. Prevention of damage to the disulphide bond content of the hair fibres would also appear to be desirable to reduce splitting and improve the manageability of hair. There would also appear to be some advantages in increasing the cross-link content of hair by the introduction of cross-linking molecules. The additional cross-linking would retard fibre swelling when wet and possibly increase the wet abrasion resistance of the hair. It is also possible that such a treatment would improve the manageability and condition of the hair as well as being able to impart a permanent change of shape to the fibres. Studies in these directions are continuing. (Received: 24th February 1975) REFERENCES (1) Swift, J. A. and Brown, A. C. The critical determination of fine changes in the surface architecture of human hair due to cosmetic treatment. J. Soc. Cosmet. Chern. 23 695 (1972). (2) Brown, A. C. and Swift, J. A. Hair breakage: the scanning electron microscope as a diag- nostic tool. J. Soc. Cosmet. Chern. 26 289 (1975). (3) Robbins, C. Weathering in human hair. Text. Res. J. 37 337 (1967). 4) Robbins, C. R. and Kelly, C. H. Amino acid composition of human hair. Text. Res. J. 40 891 (1970). (5) Wall, R. A. and Hunter, L. D. Normal adult hair--structure and properties. Cosmet. Perrum. 893 (1974). (6) DiBianca, S. P. Innovative scanning electron microscopic techniques for evaluating hair care products. J. Soc. Cosmet. Chern. 24 609 (1973). (7) Robbins, C. R. and Kelly, C. H. Amino acid analysis of cosmetically-altered hair. J. Soc. Cosmet. Chern. 20 555 (1969). (8) Miyazawa, F., Nozaki, F. and Tamura, T. Studies on damaged hair. Proceedings 8th Inter- national Congress IFSCC, London. C8 (1974) (Blackwell Scientific Publications, Oxford). (9) Feughelman, M. and Chapman, B. M. The swelling of wool fibres with reduced disulphide content in 98 % formic acid. Text Res. J. 36 1110 (1966).