Amino Acid Content of Damaged Human Hair

Summary

To verify the nature of the damage caused to the hair by particular treatments, the rate of acid and alcaline hydrolysis of the healthy hair keratins, at temperatures from 25 °C to 110 °C, in time spaces from 15’ to 72 h were investigated.

The treated hair showed, on the one hand through the SEM, important morphological alterations according to 15’-30’ (HC1 1:1) - and 24 h (thyoglycollate)-treatments; on the other hand, the HC1 1: 1-treatments gave an hydrolysis of the keratins (trough autoanalyzer) below 2% (average 0,7%) within 30’, and about 6–10% within 1 h.

In our research on hair damaged both by mechanical treatments (Morganti et al. 1977) and by certain reagents (Muscardin et al. 1977) we investigated how much some particular congenital syndromes can influence the amino acidic content of the hair keratin (Dawber and Comaish 1970, Voglino 1974, Morganti et al. 1977, Muscardin et al. 1977, Dubré et Bonafé 1978).

The experimental conditions to completely hydrolyze hair keratins as well as milder ones, to make the treatment selective, were investigated (Robbins 1970, CNR-Report 1978).

Treatments carried out on healthy hair yielded results according to the different amino acids. The yields of some amino acids were independent of the time or temperature, the yields of others were related more or less to such experimental conditions.

A treatment with sodium hydroxide, even in fairly diluted solution (abt. 0.2 N), probably for the strong temperature conditions (110°C), gave rise to strong alterations both on the consistency of the hair keratin and on the amino acid yield.

Treatment with strong acid (HCl 1:1) were carried out in the range from 15’ to 72 h at two temperatures (70 °C and 110 °C). The alterations caused in the external hair look and structure are clearly shown in Fig. 3. The results of the above treatments were compared with those obtained by ammoniacal thioglycolic acid under conditions as above.