The majority of hair bloggers (and even some hair companies) have written posts describing hair porosity basics. They make it sound like an indisputable hair science fact, when in reality, hair porosity appears to be a consumer-generated theory supported by a questionably low amount of scientific evidence. This post is the introduction and the start of research into the plausibility of this theory.

To start things off, for those who are unfamiliar:

Hair porosity basics according to the internet:

The hair blogosphere’s definiton of hair porosity is the following (direct quote from NaturallyCurly.com):

Porosity refers to how well your hair is able to absorb and hold moisture. It is affected by the flexible outer hair layer called the cuticle, which determines how easily moisture and oils pass in and out of your hair. For most, porosity is genetic, but it can also be affected by external factors such as exposure, heat treatments and chemical processing. Knowing your hair’s porosity can help you choose the right products to keep your hair well-moisturized, supple, strong and shiny.

NaturallyCurly, along with dozens of other websites and blogs sure seem to have a lot of info about hair porosity basics, and they go on to recommend products and regimens based on what porosity type you are….

But wait! Nobody is citing any sources!

Neither the two websites above nor any other websites on the first 5 pages of Google cited ANY sources for their statements!  Not a SINGLE blog or website cited a SINGLE scientific reference that supports the porosity theory (and yes, I actually went through all of them).

Additionally, there’s a problem with the GP (General Public) definition of porosity.  Namely, it’s not the same as the engineering and hair science definition of porosity [2], which is just:

The ratio of the volume of interstices of a material to the volume of its mass.   –Merriam-Webster Dictionary

However, the GP definition found on all the hair blogs bundles porosity and water absorption into one statement, which sets the stage for possible misunderstandings and wrong conclusions (more on that later).

Does this worry you?  It should. What we have here is a bunch of scientific-sounding advice that could be factual, or could be a game of online “telephone” gone wrong. So far, nobody has given us any proof for the former.

Speaking of science….

There is no scientific literature to directly support the porosity theory.

**GASP**

Over the past 70 years of hair research, no peer-reviewed scientific literature has directly identified porosity as a relevant aspect of healthy hair maintenance.  Furthermore, no studies have been published about different hair care products being beneficial for “different porosity levels.”

Sure, there are studies that mention some of the foundational claims of the hair porosity theory. For example, damage and daily weathering causes high porosity [1-3], and high porosity can be “alleviated to a certain extent” by conditioners specifically in the context of hair dye penetration [2]. However, no studies or reviews have defended the full theory as we seen it online today, and many of its claims remain unverified.

So if the porosity theory didn’t come from scientists, what source/s did it come from? That’s an interesting topic for a history post, but for now it doesn’t matter. What matters is that 1) we don’t know if its backed by science, and yet 2) websites and blogs are using it to sway our product purchasing decisions and hair care habits.

Of course, absence of evidence is not evidence of absence.  And we might start seeing scientific literature that tests the theory directly.  But while we wait for that to happen, we can at least check if its plausible…

Breaking the porosity theory down into verifiable statements

For the porosity theory to be plausible (note: I did not say valid or correct), all of the following statements/claims must be either supported by scientific evidence, or at least not rejected by it:

• Individual people’s unaltered (virgin) hair has varying degrees of porosity based on genetics.

  • It is possible to accurately predict or test at home the degree of porosity.

• The varying degrees of porosity are correlated with varying levels of water absorption.

• The varying degrees of porosity are separately correlated with varying levels of water retention.

• Despite genetic variation in porosity, there exists an ideal amount water that is constant for everyone’s hair.

  • A specific degree of porosity is paired to the ideal amount of water ( termed “normal porosity”).

  • The ideal degree of porosity is precisely in the middle of the porosity spectrum.

• It is possible to alter the level of water absorption and retention by altering the degree of porosity.

• It is possible to alter the degree of hair porosity to a significant and cosmetically-obvious end result by using hair care products.

For the next post in the porosity sequence,  we will start to look closely at these claims and talk about any studies that support them.

Stay tuned!

References:

1. Bhushan B. Nanoscale characterization of human hair and hair conditioners. Progress in Materials Science. 2008;53(4), 585-710.
2. Harrison S. Sinclair R. Hair colouring, permanent styling and hair structure. Journal of Cosmetic Dermatology, 2003;2(3‐4), 180-185.
3. Hessefort YZ, Holland BT, Cloud RW. True porosity measurement of hair: a new way to study hair damage mechanisms. Journal of cosmetic science, 2008;59(4), 303.