Conditioning Agents for Hair and Skin

Evaluating Effects of Conditioning Formulations on Hair 311
acaitering Angle /°
Figure 5 Goniophotometric curves of fibers illuminated (at an incident angle of 45°)
using unpolarized white light. Data have been normalized so peak intensity corresponds
to unity. (From Ref. 38.)
A quantitative measure of luster can be calculated by the following
formula:
where L is luster or shine, D is integrated diffuse reflectance, 5 is integrated
specular reflectance, and Wi% the width of a specular peak at half-height.
The shape of the light-scattering curve for untreated hair, and thus the
intrinsic luster of hair, depends on the state of the hair surface and the degree
of hair pigmentation. An increase in melanin content in dark-colored hair
reduces the intensity of light scattered on the internal cuticle surfaces and on
other internal elements of hair structure. This results in lowering the diffuse
reflectance and sharpening the specular peak, consequently providing an increase
in hair luster. For damaged hair, in which the surface layers of cuticles
are jagged and uneven, the intensity of scattered light (diffuse reflectance) is
high to the point that the incident reflection peak can appear as a broad plateau
rather than a sharp peak. It has been demonstrated that some types of
hair treatments, including conditioning hair rinses, can increase the "sharpness"
of the specular reflection and thus improve the luster of damaged hair.
On the other hand, it was found that the luster of intact, undamaged hair,
characterized by a well-defined and "sharp" specular reflection, cannot be
increased by application of conditioning rinses or conditioning shampoos, which