Hair surface quality: Laser scattering as a tool for characterizing the surface condition and deposits from shampoos and conditioners.

Objectives: The hair surface condition underlies many visually perceived attributes such as shine, colour and the 3D perception of a curly hair style. Many factors can alter the hair surface such as cumulated cleansing/styling regimens or chemical treatments which can lead to degradation of the cuticle edges and surface. Similarly, pollutants, sebum, and shampoo/conditioners can build up on the hair surface which are also perceivable to an observer.

Methods: The highly directive light of a laser is reflected and scattered by the surface of hair fibres into a circular pattern. The angular and spatial characteristics of this pattern reflect the hair geometry and the quality of the hair surface, i.e. the outer cuticle layer. Dark flat hair tresses were used to measure the impact of artificial sebum and shampoo/conditioner regimens on the cuticle surfaces. Also, longer single hair fibres from 4 volunteers were characterized for their surface changes from roots to tips, i.e. over the chronological age of the hair.

Results: The laser scattering shows clear changes in specular reflection characteristics from treatments and allows for the extraction of the cuticle inclination angle with respect to the hair axis. Deep cleansing or clarifying shampoos do partially restore the cuticle angle by removing residues on the hair surface whereas more conditioning systems can lead to changes in specular reflection angle and scattering, especially for multiple cycles of shampoo + conditioner treatments. Lastly, changes in hair surface can be traced over time of hair age by this approach and are consistent with frequency and nature of hair treatments.

Conclusions: The method shows great potential for characterizing cleansing regimens in terms of their impact on the hair surface, either as single or multiple washes. Coverage or damage to the hair cuticles appears readily as an angle shift of the specular reflection whereas the quality of the surface topology has a direct impact on the angular width of the specular reflection thus affecting the shine band on a person's head. Hair ageing from root to tip can be quantified by laser scattering and correlates well with treatment events in time.