Porosity in its simplest form relates directly to the ability, or inability for hair to absorb water
or chemicals directly into the cortex. All hair is naturally permeable and porous to water.
However, the degree of porosity will vary by the individual, the condition and shape of the
hair’s cuticle layers. If your hair faces a traumatic styling event such as chemical relaxing or
permanent coloring, the protein structure is attacked and the protective cuticle shielding
becomes ragged and torn. Therefore, hair in this condition is said to be porous.
In order to glean more knowledge, it is useful to visualize hair as a wooden fence. A new
fence is durable and has the capacity and ability to shield the yard it surrounds. The new
fence can endure rain, sun, storms and the majority of the elements which may be thrust
upon it. Overtime as the fence ages, the wood in the fence begins to soften, and the fence’s
once protective barrier becomes vulnerable and can be breached. Often, holes may
appear in the fence or some planks may become missing. The fence has become porous.
This example relates to how our hair functions. When aging, the protective cuticle layers
begin to peel, crack and lift away. A change in the presentation of the cuticle’s shape
makes the hair less durable and able to absorb and hold the moisture it vitally needs.
Thus, older hair is more porous and has higher porosity, than the newer hair. Porosity
increases as we move from the roots to the ends of the hair as this represents age
progression along the fiber.
Hair will not readily absorb moisture and resists chemical treatments if it has
low porosity. This type of hair is generally quite healthy and has not been exposed
to cuticle-degrading treatments. In low-porosity hair, the cuticle imbrications
and/or or ridges along the hair shaft are tightly shut just as when the hair first emerges
from the hair follicle. The assault on the hair due to everyday living, chemical processes
and styling eventually takes a toll on the cuticle scales and causes them to lift and lose their
tightness over time. Black hair has been known to have low porosity naturally. It is usually
less porous than Caucasian or Asian hair types etc, unless it has received chemical process.
You will often find that the majority of individuals will have hair somewhere in the middle
of the two extremes of porosity: a.) Hair with good porosity that retains moisture well
and b.) Hair that accepts chemical treatments like coloring or relaxing if desired.
There is an intricate connection between the hairs pH balance and porosity. As such,
Low-pH products and styling treatments diminished the hair’s porosity by constricting
the cuticle causing it to tighten. However, high-pH products have the opposite effect
and increase the hair’s porosity by swelling and lifting the cuticle scales.