Repeated exposure of hair to UV irradiation and to water (at washing) can influence the quality and/or quantity of EP and SP in the hair fiber. We assume that such changes should be detected when sections of hair are compared from a distal position with those positioned proximal to the root of the hair (if hair is long enough).
For this study eight healthy subjects with hair at least 20 cm long were invited to participate. 5-cm long hair fragments were cut from each sample: proximal (as 0–5 cm from hair root) and dis- tal (as 15–20 cm from hair root).
The assay of EP and SPe was performed as described earlier. The results are summarized in Table 2.
According to data shown in Table 2 quantity of SP in the hair fibers grew going from proximal to distal fragments. SH-content of SPe decreased with hair length. Presumably, repeated UV irradi- ation destroys cystine in hair keratins and the peptides that were formed after disulfide bridges fission were washed away.
The specific fluorescence intensity of EP and SPe for tryptophan from the proximal hair fragments was lower than the equivalent values for the distal fragments (p < 0.05 both for EP and SPe). The specific fluorescence intensity shifts, when adjusted for protein concentration or for hair weight showed similar tendencies. How- ever for the ratio of F(350) to hair weight the effect was more pro- nounced (Fig. 6). Apparently a gradual loss of tryptophan occurs from the shaft, this agrees with the data in Table 2.