Okay, impatient people, LOL. Here are my thoughts on porosity.
There are a lot of myths out there about hair porosity and how it relates to curly hair care and maintenance. Let's see if we can't set some of the record straight.
Porosity is, simply put, the hair's ability to absorb and retain moisture. Porosity is a critically important factor in determining one's curly hair care. Since moisture is what defines and shapes our curls, the inability to keep moisture within the hair shaft will defeat the most valiant efforts to maximize curl potential.
If you don't know your hair's porosity, you won't be able to make the best product and maintenance routine choices to maximize the amount of moisture your curls retain. The existing "curl classification systems" never, ever mention porosity in their classification process. Since lack of moisture is one of the biggest causes of frizz, I personally find that odd in the extreme. Just one more reason I don't find those systems very helpful or informative.
Your degree of porosity is directly related to the condition of your cuticle layer. Healthy hair with a compact cuticle layer is naturally resistant to penetration. Porous hair has a raised cuticle layer that easily absorbs water, but is quick to lose moisture as well. The texture of your hair is not an indication of its porosity. Different degrees of porosity can be found in all hair textures. For example, although coarse hair normally has a low porosity and is resistant to chemical services, coarse hair can also have high porosity as the result of damage or previous chemical services.
There are three different levels of porosity:
Hair with low porosity is considered "resistant" hair. Low porosity is when the cuticle of the hair shaft is too compact and does not permit moisture to enter or leave the hair shaft. Hair with low porosity is much more difficult to process, is resistant to chemical services, and has a tendency to repel product rather than absorb it. Chemical services performed on hair with low porosity require a more alkaline solution than those on hair with high porosity, to raise the cuticle and permit uniform saturation and penetration.
Hair with average porosity is considered "normal" hair. With normal porosity, the cuticle is compact and inhibits moisture from leaving or entering the hair shaft; however, it allows for normal processing when a chemical service is performed -- according to the texture -- and will readily absorb and retain product properly formulated for this hair type.
Hair with high porosity is considered "overly porous" and is the result of previous overprocessing. Other factors that can also affect porosity include heat damage, chlorine/hard water/mineral saturation, sun damage, or use of harsh ingredients. Overly porous hair is damaged in some way, and is dry, fragile and brittle. It has an open cuticle that both absorbs and releases moisture easily; it processes very quickly and can be easily damaged even further if extreme care is not taken when a chemical service is performed. Although overly porous hair absorbs product quickly, it is often dry as the open cuticle does not allow for product retention within the hair shaft. Chemical services performed on overly porous hair require less alkaline solutions with a lower pH, which will help to prevent further overprocessing.
Porous hair accepts haircolor faster and permits darker color than less porous hair; however, although overly porous hair takes color quickly, color also fades quickly. While hair with low porosity is difficult for chemicals to penetrate and takes a longer processing time, the color will last much longer.
You can check porosity on dry hair by taking a strand of several hairs from four different areas of the head (front hairline, temple, crown and nape). Slide the thumb and index finger of your other hand down each hair strand from end to scalp. If it is smooth, you have normal porosity. If your fingers move very fast up the hair strand and it feels exceptionally slick, dense and hard, you have low porosity. If your fingers "catch" going up the strand, feel like they are ruffling up the hair strand, or if the hair strand breaks, your hair is overly porous.
Unfortunately, porosity issues stemming from irreparable hair damage CANNOT be permanently corrected. Only time can truly mend damaged hair. You can, however, create a temporary fix until the damaged part grows out by "reconstructing" the hair shaft with protein treatments. Protein fills in any holes within the cortex (inner layer of the hair) and also helps to fill in the gaps exposed by a raised cuticle.
Individuals with coarse hair, however, must be cautious: putting additional protein on coarse hair can dry it out even more. For those with a coarse texture, acidic treatments such as apple cider vinegar rinses are likely a better alternative as your hair already manufactures an overabundance of protein naturally.
(Which brings to a small derail. I know people are tired of me harping on the excessive use of shampoo bars. If, however, you have porous hair, you are not doing yourself any favors by using them. These bars are fairly alkaline and raise the cuticle, the exact opposite of what people with overly porous hair are trying to achieve. Your goal is to establish a routine and determine the most effective product use for your hair without swimming upstream in the process.)
So, what does this mean for the curly girl? It means you need to determine your hair texture and your hair porosity, and then think about what types of products are best suited to your particular hair type. Other factors will come into play, but these two hair properties are the most important properties to know.
Next, I'm going to touch briefly on hair elasticity and density. Although not nearly as critical as texture and porosity, they still play a role in determining the most effective curly hair care routine.