* Porous Structure: Hair isn't a solid, impermeable strand. It has a porous structure, especially the cuticle (the outermost layer) when damaged or lifted. This porosity creates spaces where oil can be trapped and absorbed.
* Lipophilic Nature: Hair is naturally lipophilic, meaning it attracts and binds with fats and oils. The protein that makes up hair, keratin, has regions that are non-polar, and these regions have an affinity for oils.
* Cuticle Condition: A healthy cuticle layer lies flat, which helps to repel excess oil. However, when the cuticle is damaged (from heat styling, chemical treatments, or harsh washing), it becomes raised and rough. This roughness increases the surface area available for oil to cling to, and the lifted scales allow more oil to penetrate the hair shaft.
* Capillary Action: The gaps and spaces between hair strands create an environment for capillary action, similar to how a paper towel absorbs water. This action pulls oil upwards from the scalp along the hair shaft.
In summary, hair's porous structure, its chemical affinity for oils, and the condition of the cuticle all contribute to its ability to absorb oil.