Hair Science: Why is Hair Porosity Important?

No matter what natural hair circle you travel in, I am sure you have heard a lot of talk about hair porosity.  From tests to determine your hair porosity to product selection based on hair porosity, it seems like this one characteristic is the key to everything natural hair. While this is a bit of an exaggeration, understanding hair porosity can help you develop a better hair regimen.

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What is hair porosity?

In order to dive deeper into exactly what hair porosity means, we must first understand the basic structure of the hair strand.  Thicker hair fibers typically contain three distinct structures: the medulla, the cortex, and the cuticle.  The cuticle is the outer layer of the hair strand that serves as a protective barrier.

A cross-section of the human hair fiber.

The cuticle layer is structured as overlapping layers of keratinized scales. In new hairs, genetics is the primary determinant of how tightly the scales are formed. When the scales are close together and create a smooth surface, it enhances the strength and protection this outer layer offers to the inner cortex. However, as the cuticle layer becomes weathered over time, the scales can become more frayed and damaged with even complete removal of some scales in the process. The degree to which this outer cuticle layer is opened determines how porous or penetrable the hair strand will be. Hence, hair is often classified as having either low porosity, normal porosity, or high porosity.

Scanning Electron Microscopy (SEM) of a human hair strand (x1000)

How does hair porosity impact hair care?

Low Porosity

In low porosity hair, the scales of the cuticle layer fit tightly together. This tight-fitting structure does not easily allow movement of water and other chemicals back and forth. Because of this repelling nature, hair product build-up is a concern as heavy product application can lead to a coating of the hair strand that makes conditioning and moisturizing even more difficult. Opening the cuticle layer through heat can increase the penetration and conditioning of the hair strand while using lighter water-based products can prevent build up. The compact nature of the outer layer will help strands to retain moisture over time.

High Porosity

When the cuticle layer is open and highly porous it can easily absorb moisture into the hair strand. However, it can also lose moisture to a similar degree. This porous nature can also lead to dry and brittle strands but for a very different reason than previously discussed with low porosity. In this case, moisture retention becomes key to healthy hydrated hair. The goal in this instance is helping to restore the outer cuticle layer so that there is a balance between what goes in and out of the hair strand. Ingredients such as oils, butters, and silicones are often used in formulations to help coat the hair creating a barrier that reduces moisture loss.

Normal (Medium) Porosity

In between low and high porosity is what many may consider a sweet spot. This is the most resilient of the porosity categories. Normal or medium porosity hair typically refers to the cuticle layer being open just enough to allow moisture to penetrate without difficulty and be maintained within the inner cortex. Styling can often be simplified; as the range of styling product options is greater and enhanced techniques to either increase hydration or retain moisture are not routinely necessary.

The degree to which this outer scaly layer is opened determines how porous or penetrable this layer of the hair will be.”

Can you change the porosity of your hair?

Hair porosity is largely based on genetics and some change will occur with aging of the hair. However, the ability to alter the porosity of your hair is driven by improving the overall health of the hair. Weathering of the cuticle layer will naturally happen as a result of environmental factors, shampooing, combing, and other styling. The proper selection of hair products to protect, condition, and detangle the hair can help reduce friction and tangling that can lead to cuticle disruption. Also, avoiding hair color and other chemical services can reduce the porosity of the hair if a change is strongly desired. The key is to focus on using the knowledge about why porosity matters to create a hair regimen that improves hair health and then watch all of the pieces fall into place.

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