Driving Innovation by Decoding Hair’s Relationship with Water

Whenever hair comes into contact with water (e.g., while washing) the interaction of this water with hair can take several forms. Firstly, there is dripping water and capillary water, the water between the hair fibres, which can both be easily removed by towel drying. But there is also another type of water, structural water, which is inside the hair fibre and causes it to swell. Recently, Kao’s Basic Research and Technology Development Team in the European Research Laboratories in Darmstadt analyzed the interactions of structural water with the microscopic substructures of hair from the nanometer scale up to macroscopic observations. Using the Atomic Force Microscope (AFM), the mechanical properties of the various hair subcompartments have been found to show a strong dependence on relative humidity, RH¹, while more recently the team have discovered that the cuticles, the outermost layers of hair, can swell significantly more than previously thought². A detailed study on the interaction of hair with water was also presented at a global hair science conference in June 2025³ .