A STUDY OF DAMAGED HAIR 159 Cosmetically-altered hair Cosmetically-altered hair had an appearance very similar to virgin hair, when no split ends were detected. The hair appearance shown in Figs 1-6 for virgin hair, can also be seen in cosmetically-altered hair. However, there are also other types of breakdown associated only with cosmetically-altered hair. Fig. 7 shows a split end from hair that has had one permanent-wave applica- tion. Unlike virgin hair, where splitting was only observed after almost all of the cuticle was removed, hair that had been permed or bleached was often observed to split whilst the cuticle was still clearly visible. It was observed that splits and general shaft damage could also occur well away from the end. Fig. 8 shows shaft damage detected about 10 cm from the end of a fibre that had been permed once and the perm did not 'take'. The third important factor of cosmetically-altered hair was the extent of splitting. Virgin hair less than 15 cm long was hardly ever observed to split, whilst cosmetically-altered hair less than 15 cm long was often observed to split. This was detected as most likely to occur when a perm 'went wrong' or did not 'take', and on some bleached hair. Also, the splits and shaft damage associated with hair that had been permed or bleached, was generally observed to be far more severe than for virgin hair. That is, cosmetically-altered hair was observed to contain far more of the hair categorized as fly-away fibre (6) than virgin hair, for hair fibres of the same length. The reason for this additional deterioration associated with cosmetically- altered hair is not immediately apparent. Swift and Brown (1) have shown that very minor changes in the surface structure of hair occur immediately after perming and bleaching, but these are not likely to be directly responsible for the observed additional damage. It is probable that these processes have chemically altered and weakened the hair and then during subsequent physical treatments, the altered hair is unable to withstand the abrasion normally associated with hair grooming to the same extent as can the virgin hair, and a greater degree of fibre splitting results. Robbins and Kelly (7) and Miyazawa et al. (8) have found a reduction in the cystine content of bleached and permanent-waved hair. It is primarily the cystine content of keratin fibres, through the cross-linking associated with the disulphide bonds, that gives these protein fibres their high mechanical stability. It seems probable that the reduced fibre cross-link content associated with these treatments is responsible for loss of physical strength associated with these fibres. Feughelman and Chapman (9) have shown that the relative cross-link density of keratin fibres can be ascertained by a determination of the diametral swelling of the fibres in 98• formic acid. This provides a convenient method for the determination of a relationship between fibre cross-link and splitting caused by the mechanical abrasion associated with hair grooming.

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.