HUMAN HEAD HAIR AS FORENSIC EVIDENCE 307 surface of the hair constitute the large part of the colour sensation. The other major limitation in hair colour comparisons is that human hair dis- plays a very limited range of hues (581-606 nm), i.e. human hair differs mainly in the lightness or darkness of the colour, not in the wavelength of the reflected light. The 200 hair tufts were therefore compared with commer- cially available dyed nylon tufts (Wella (28)). Only 29 colour tufts were used to describe the colour of the hair samples, but on extending the colour com- parisons to single fibres a hair colour chart containing 29 colours merely led to ambiguity in assigning the hair colour. This is because the colour of single fibres from a given individual varies along the length of the fibre and across the head of that individual. Successive experiments indicated that nine hair colours (from black to white) provided sufficient colours to describe the population with minimum ambiguity in assigning the particular colour. It is neither necessary nor desirable to use more than nine colours to describe hair because of the range of hair colours displayed by a given individual. Some of the individuals examined displayed a range of colours from group 3-6 and 2-5 (Table I). Hence it is important to have sufficient controls to establish the range of hair colour displayed by a given individual. A single fibre was chosen from the hair of each of 200 individuals at random and compared with the hair chart containing nine colours. A hair was described as grey/white if the original tufts prepared contained too many white hairs to preclude colour comparisons. The results of this survey are shown in Table I. Table I. Distribution of hair colour in population Very dark Dark White Black brown brown Mid-brown Blonde •grey Colour group 1 2 3 4 5 6 7 8 9 Female % population 0 28 20 9 14 7 6 4 12 Male % population 0 43 16 12 9 1 0 0 19 Table I shows that a large proportion of the colours of the male and female population lie in groups 2, 3, 4, 5, 9. The remaining groups 1, 6, 7, 8 are sufficiently rare to provide useful discrimination. It can also be seen that no black hairs or genuine red hairs were found in this survey. So-called blonde hair (groups 6, 7, 8) were sufficiently rare in both male and female

308 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS populations to provide meaningful information. It can be seen that 17•o of the hair of the female population can be described as blonde, whilst for the male population only 1 •o of male hairs were blonde. In group 6, six out of seven women had blonde hair as a result of chemical bleaching whereas, not surprisingly, none of the male population had bleached hair. One of the six females in group 7 had bleached hair, whilst one in four females in group 8 had bleached hair. Hence it will be obvious that a blonde, bleached hair is more likely to be female than male. A blonde female unbleached hair repre- sents only 1 •o of the female population, and therefore it may be concluded that hair lighter than group 5, i.e. 6, 7, 8 can provide useful information. Identification of hair cosmetic treatments Bleaching The use of commercially available bleaches to lighten hair brings about the bleaching of the hair pigment (melanin), together with structural damage to the tt-keratin (hair protein). The cuticular layer containing the tt-keratin is gradually abraded away due to the movement of individual hairs across one another and by brushing and combing. The extent of the damage to single fibres can be estimated by observation of the uptake of dye from an aqueous solution of methylene blue. The amino-acid composition of bleached hair is not greatly different from unbleached hair, with the exception that, in the former, a high proportion of the cysteine and cystinc is converted into the corresponding sulphonic and cysteic acid. It is the pre- sence of the anionic sulphonic acid groups which is responsible for the up- take of methylene blue (a cationic dye). It is apparent from the present work that the degree of hair damage is closely related to the extent of hair bleach- ing. For a given bleached fibre the uptake of methylene blue is greater at the tip of the fibre and least near the root. It has been established that if 1 cm lengths of hair are obtained from the same head but from different hairs and from the same distance from the root, then methylene blue uptake is similar in each case. The methylene blue test is therefore a useful compara- tive test for assessing hair damage caused by chemical bleaching. No other cosmetic treatments have been found to interfere with the methylene blue reaction. The occurrence of bleached hair for the different colour groups is shown in Table II. Technique. A 1 cm portion of hair is fixed to a cavity slide using perspex cement or cellulose acetate, and several drops of aqueous methylene blue solution (0.5•o) added to completely cover the hair. After 4 min the hair is