Chapter 10 363 in sample weight, which we hypothesize to be the consequence of oil adsorbing on the hair surface. However, subsequently, the baseline is observed to gradually drift upwards as apparent slow internal adsorption is believed to occur. It should be noted that this behavior reverses when the relative vapor pressure is reset to zero. That is, there is fast initial desorption (believed to be removal of surface material) followed by a gradual decrease in baseline as these molecules slowly diffuse out of the hair. We have performed similar experiments with other volatile oils (including cyclomethicone and fragrance components) with comparable findings. As such, there is evidence suggesting the ability for oils to penetrate into hair, yet the rate appears very slow. Summary Hair care approaches predominantly focus on manipulating the surface properties of fibers. Shampoos clean the exterior, while conditioning treatments leave behind deposits that provide Figure 23. Adsorption of decane by hair. Relative vapor pressure stepped from 0–90% at 25oC