The Effects of UV Radiation on the Flexibility of Hair Cuticle

Abstract

In order to determine the effects of UV radiation on the hair cuticle, observations were made, by means of environmental scanning electron microscopy (ESEM), of cuticle cell lifting at the knot of a single hair in which a certain level of tension was produced by the tying of the knot.
In hair exposed to solar radiation, or to UVA or UVB irradiation, cuticle cell lifting was produced in proportion to the dose of UV radiation. It was shown that UVB produced most marked effect, whereas unirradiated hair revealed little change in cell lifting.
Observations made using transmission electron microscopy (TEM) showed that there was a tissue change in δ-band in the cell membrane complex (CMC) of the cuticle of UV irradiated hair, and that this was the major site of lifting. Also, electron staining at the endocuticle was less than was the case with unirradiated hair, a clear indication that the hair underwent denaturation. Moreover, there were gaps in some parts of the endocuticle layer.
It was found that the rate of swelling of UV irradiated hair was reduced when it was soaked in a 5% thioglychollic acid solution (pH 9.6). This could be explained by the mechanism that a denaturation of δ-band and endocuticle, the non-keratinous tissue of the cuticle, caused reduced permeability of the UV irradiated hair.
All these findings seem to suggest that the cuticle will lose its strength as a result of the decomposition of the constitutive amino acids, such as cystin, caused by UV irradiation, and the relatively flexible non-keratinous tissue (δ-band, endocuticle) will denature, losing its flexibility.
Moreover, a similar examination of permed and bleached hair revealed no marked degree of cuticle lifting in either of them, and showed that the reduced flexibility of the cuticle was a form of damage peculiar to UV irradiation.