How Porous is Your Hair?
Your hair’s porosity is its capacity for absorbing and retaining moisture. It’s determined by the condition and integrity of the cuticle.
As a general rule, there are 3 levels of porosity: low, medium and high.
When the cuticle scales (or shingles) lay flat and overlap each other, the hair has low porosity because the cuticle shield is air (and water) tight. Moisture struggles to get in and out.
Hair that has medium porosity has a more relaxed cuticle. Moisture can penetrate the hair shaft and is slow to seep through the angled cuticles.
Hair with high porosity has raised or irregular cuticle scales. As a result water enters and exits the hair strand easily.
Make sense? Well, to further complicate things, it’s likely your hair has different levels of porosity throughout your head.
But, no worries. It’s unlikely you’ll have highly porous and very low porous hair on one head unless you’ve damaged your hair with excessive heat and chemicals.
So, why do you need to know your hair’s porosity? Well, it’s the same as knowing your body’s needs. If your body needs more water, vital systems will start to shut down or work overtime, so obviously, you need more water. Same goes with hair.
Porosity and the hair cuticle
The hair cuticle is made of several layers of scales that are in close proximity to one another — like roof shingles. They provide insulation for the hair’s inner core, the cortex. The cortex is coated with a seal of sebum — the natural oils our bodies produce.
Note the sebaceous (oil sack) gland in the diagram below. This gland produces the sebum — a protective layer of oil — on our skin and hair.
Ideally, sebum provides elasticity and protects against too much water getting through the cuticle into the cortex.
The cortex is made of a lattice of keratin protein fibers.
Too much water weakens them. The hair breaks or tears under the strain of the water weight and weakened protein fiber.
Permeable and Impermeable
When hair cuticle scales are raised, farther apart or positioned in an irregular pattern, moisture easily enters and escapes. Therefore, hair that is highly porous is highly permeable. That’s why people with naturally porous hair or damaged hair struggle with so much dryness. Added oil onto the hair shaft — such as jojoba or olive oil — seals in moisture which, in turn, increases hair’s elasticity and prevents breakage.
On the contrary, hair that’s typically low in porosity is impermeable — it doesn’t absorb liquids easily.
According to L’Oreal Hair Science, healthy, unaltered hair can absorb up to 30% of its weight in water. Damaged hair or hair with raised cuticles can absorb more than 45% water which can cause hair to swell up to 20% in diameter.
Porosity and Chemical Processes
In order for chemical relaxers or hair dyes to permanently alter hair structure, the hair color or lye has to penetrate the hair cuticle. So, the cuticle must be forceably raised. Usually that’s done with a self-heating process, a developer or lye.
So, let’s be clear, any permanent or semi-permanent process is meant to intentionally damage your hair so it will look a certain way.
The Usual Suspects
According to blackhairscience.com, the level of hair porosity can be the result of the integrity of the individual scales of the cuticle. Over time and wear, cuticle scales can become weak and can even develop holes in them.
Hair porosity can be altered by:
- Heat styling
- Too much combing and brushing up and down the hair shaft
- Sun and environmental exposure
- Chemical processing
- Cleansing and shampooing with sulphates
Natural Porosity: You’re just born with it
Your natural hair’s porosity is — like anything else — the result of your genetics. The cuticles on your hair can be wide, tight and lay flatly on your hair shaft causing low porosity or they’re irregular in size, shape, angle and placement resulting in high porosity.
Are you starting to get the picture? Just as every snowflake is unlike any other, every hair strand is unlike any other. And every head of hair is as individual and unique as a fingerprint.
Milady’s Standard Cosmetology, 2012 Edition, http://www.milady.cengage.com/9781439059302.asp
“Properties of Hair,” L’Oreal Hair Science, http://www.hair-science.com/_int/_en/topic/topic_sousrub.aspx?tc=root-hair-science%5Eso-sturdy-so-fragile%5Eproperties-of-hair&cur=properties-of-hair
“Hair Porosity,” http://www.naturallycurly.com/texture-typing/hair-porosity
“Hair Porosity Basics,” The Science of Black Hair, http://www.blackhairscience.com/porosity-concerns/