The water and water soluble materials such as shampoos and conditioners can easily penetrate into the cortex of hair via the channels between cuticle layers where CMC of the cuticles reside. The empty spaces in CMC of cuticles also play a major role in the penetration of shampoos and other solvents into the hair. The mechanism of this penetration path is shown in Figure 2.10. The pathways are between the cuticles layers that are layered around the fiber cortex at 5 degree angle, as shown in the Figure 2.10.
Figure 2.10: The penetration of shampoos and conditioners into cortex via channels of cuticles
The reactive chemicals consisting of high pH such as relaxers, permanent waves, permanent colors and hair lighteners penetrate laterally through the cuticle layers, CMC of the cuticle-cuticle layers, CMC of the cuticle-cortex junction, and the CMC of the cortical-cortical cells. The CMC of the cortical-cortical cells is the weakest one and damages easily with solvents and high pH reactive chemicals. The schematic of the flow of chemicals is shown in Figure 2.11.
Figure 2.11: The lateral penetration of reactive chemicals into the hair cortex via cuticles.