Hair porosity refers to its ability to absorb and retain moisture. The hair fiber is surrounded by scales (cuticles), which are more or less open—like those of a pine cone—and which absorb varying amounts of the water you apply to your hair.

The level of porosity depends on the degree to which the hair cuticles are open. The more open the cuticles, the easier it is for water to enter the hair… but also to escape. Conversely, the more closed the cuticles, the more difficult it is for water to penetrate and escape the hair.

It's natural: no one's hair porosity remains the same throughout their life. Hair adapts and has this natural ability to open or close its cuticles depending on various factors. However, some of our hair care habits can permanently destroy this ability in hair that has already grown.

A test can be used to assess hair porosity: the water glass test. It involves filling a glass with water (preferably soft water) and placing one or more strands of hair in it. Then, simply wait 3 to 5 minutes to observe how the hair absorbs the water.

If the hair sinks to the bottom of the glass, it means it has high porosity . The cuticles are therefore wide open. Water penetrates easily, but it evaporates just as quickly, making the hair dry out easily.

If the hair remains halfway open, the porosity is considered good . The cuticles are therefore moderately open.

If the hair remains on the surface, it means it has low porosity. Therefore, the cuticles are closed or only slightly open.

Our actions, our care, our hairstyles and even the climate influence the hair's ability to open or close its cuticles.

Here are some care tips depending on hair porosity.

Deep treatments, such as masks, are often performed with steam baths to allow the treatment to penetrate deeply and open the scales.

Humectants (such as vegetable glycerin, honey, etc.) help retain hair moisture. Their role is to absorb and retain water, even from the air. Adding them to your daily moisturizing routine is a good idea. This way, regardless of your hair's porosity level at any given time, it will always have water available: either from the air or from your hair care products.

The temperature of the water used for moisturizing or washing also helps to open or close the cuticles, as does the climate. Cold water tightens the cuticles, while heat opens them—which is ideal for plant-based butters like shea or oils like castor oil, especially in humid tropical climates suitable for curly hair.

The limescale present in some water, especially in the West, can clog the cuticles and make hair brittle and dry. Therefore, using the final rinse technique with mineral or soft water, combined with apple cider vinegar or lemon juice, helps to remove limescale and tighten the cuticles.

Choosing the right oils or butters for your hair's needs helps avoid ineffective treatments. Thick oils like castor or black castor oil, as well as plant-based butters like shea, can lock in moisture if your hair has low porosity.

Our hair modifications also play a role in changes in hair porosity.

Hair straightened with an iron has closed scales, because the passage of the iron straightens the hair in the direction of closing the cuticles, even if steam or heat can open them momentarily.

Certain hair treatments, such as bleaching or straightening, permanently alter the hair and damage the hair fiber and cuticles. Even the best treatments cannot restore the original structure, but they can help the hair survive despite this damage.

Because the cuticles are damaged, their natural opening and closing mechanisms are destroyed. This type of hair, having high porosity, requires deeper and more frequent care than natural hair.

The healthiest option is to cut the damaged hair once new growth is present and the desired length is reached, or more radically, without waiting.

In all cases of permeability, there are solutions ranging from mild to radical. The key is to know yourself well and make the right choices according to your needs and desires.

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