The science behind porosity, what is actually happening inside your hair
In my previous post i explained what porosity is. Today I want to show you why. What is actually happening inside the strand. Why some hair holds moisture and some cannot. And why understanding this changes everything about how you care for your hair.
The cuticle has a secret
Every hair strand is covered by a protective outer layer, the cuticle. Flat, overlapping scales that wrap around the strand like armour. But those scales are not just mechanical. They have a thin lipid coating on their surface called the F-layer. A waxy, fatty acid seal that keeps the cuticle lying flat and gives healthy hair that slightly water-resistant quality, the reason water beads on undamaged hair before it soaks in.
When the F-layer is intact, the cuticle is protected and controlled. When it is stripped away, the scales lift and can stay lifted.
That is the difference between low and high porosity at a structural level.
What strips it away
The F-layer is surprisingly vulnerable.
Alkaline products, anything with a high pH cause the cuticle to swell and the scales to lift. Most chemical services sit in this category: colour, bleach, relaxers, perms. Heat does similar damage over time by breaking down the lipid structure directly.
Every time the cuticle is exposed without recovery, the F-layer degrades a little more. Eventually the scales cannot lie flat anymore not because they are dirty or product-coated, but because the structure holding them down is gone.
This is the difference between temporary and permanent porosity. Temporary is a cuticle lifted by heat or pH that can recover. Permanent is structural, the F-layer is gone and the damage lives in the strand until it grows out.
What this means for your hair
A healthy cuticle gives you control over moisture. You can open it with warmth or steam, and close it again. Your hair absorbs when you want it to and holds on between washes. A damaged cuticle takes that control away. Moisture enters freely but escapes just as freely. No amount of conditioning fully compensates for a cuticle that cannot close. This is the science behind why some hair always feels dry no matter what you put on it. It is not the products. It is the structure.
Knowing this tells you exactly what your hair needs and what it is reasonable to expect from your routine.
Science is just your hair telling you the truth.
Always rooting for you,
— Sarah/ Staunch