Saturday, September 24, 2011

Porosity in Hair

I'm going for long-winded again, but you get pictures at the end as a reward...
Hair is a fibrous, proteinaceous system which can absorb fluids. How porous or absorbent your hair is has a lot to do with how it looks and can help you decide what to use on your hair to help it look it’s best. A porosity is a hole or a gap – an opening. For example, teeth are slightly porous and that is why they can be stained by coffee or tea. Limestone is porous and so water can run through it (a groundwater aquifer). Concrete can be porous and so the inside of concrete basements can become damp when the outside soil is saturated with water.©Science-y Hair Blog 2013

Hair which is porous will take on water and other chemicals easily because of all the tiny openings in the cuticle. Most of these openings only go from the outside world to a deeper layer of cuticle. Porous hair has little flaps of cuticle sticking up. These areas can be “patched” – stuck down or filled in temporarily by hydrolyzed proteins which bond to these damaged areas, and by conditioners and silicones, but they cannot be reversed. Proteins and conditioners also form a film over hair which creates a smoother reflective surface for greater sheen.©Science-y Hair Blog 2013

Hair which is not very porous repels water and most other fluids and this is a good thing. One need not try to force products to penetrate into it (something which occurs in porous hair more easily) because it is not losing water or materials from its interior. There is nothing to fix or replace. Hair which is porous can take up more water and this leads to greater swelling of the hair which causes further damage from the stress of the swelling. Porous hair absorbs water and absorption can damage hair. Healthy hair with a normal amount of porosity (or low porosity) adsorbs (things bond to the outside or simply dry on), but is slower to swell with water, thus protecting itself. Porous hair loses moisture and other good things more readily than less-porous hair, so it is more difficult to keep it supple and shiny and strong.
©Science-y Hair Blog 2013
What causes porosity?
Weathering of hair, mechanical stress, wetting and drying, shampooing, chemical treatments, and physical structure of hair. If your hair has waves, curls or (especially) kinks (and wavy hair can be kinky hair too), it is likely to have areas on the strand which are narrow, flattened, twisted or otherwise not as strong. Even the “cuticle armor” cannot protect these areas adequately. These are prone to breakage and damage and therefore become porous easily. Wavy and curly hair is also more prone to damage from daily life simply because it has bends in it.©Science-y Hair Blog 2013

Hair which is dry because the scalp oil (sebum) is not abundant – and sebum production decreases after age 40-50, because you have dry skin in general, because your hair is curly and thus it is more difficult for oils to spread than in straight hair, or because it is washed frequently with strong cleansers which remove all the protective lipids from hair, will tend to become porous more easily. Strong cleansers remove the lipid component of the hair’s cuticle system. You probably know that unvarnished and un-oiled wooden furniture and unpolished leather shoes are more prone to cracking and roughness and become wet more easily (leading to water damage). Hair is much the same - unprotected by the variety of natural scalp lipids it becomes wet more easily and that water causes swelling and damage.

©Science-y Hair Blog 2013
Bleaching and porosity:
The size of pores in hair (gaps in a cuticle layer) increases from small pores in chemically untreated hair to larger pores during the bleaching process. During the first minute of bleaching, pores increase by 30%. During the first 5 minutes of bleaching, hair’s pore size increases further. Through the following 10-20 minutes of bleaching, the pores created during the first 5 minutes of bleaching merge, with the result of much larger pores in hair than in the original, un-bleached hair. Any chemical bleaching process increases porosity!©Science-y Hair Blog 2013

Porosity and UV damage:
After 200 hours of ultraviolet light exposure, the surface area of cuticle in hair non-chemically treated is reduced by almost half. 200 hours is equivalent to half an hour of sun per day for just over a year. Unlike chemical bleaching, this increase in porosity is a result of many more smaller pores opening up as UV light fuses cuticle edges together. As they fuse, their coverage shrinks. This UV damage is progressive. After 1200 hours of UV exposure, pores begin developing in the layers of cuticle which were fused during the previous hours of UV exposure and the entire cuticle area may become fused together and rigid and thus susceptible to cracking – which would create more pores.
©Science-y Hair Blog 2013
Porosity and Mechanical stress:
When you comb hair, tie it up, sleep on it there are stresses from stretching, from rubbing and these forces erode cuticles too. That’s why there are several layers of cuticles – they are the protective coating for hair and damage is a rule, not an exception.
©Science-y Hair Blog 2013
Maintain Porosity:
What can you do to keep your hair’s porosity in the desirable “low to normal” range? Avoid too much handling, tight ponytail holders, excess heat (curling or straightening irons, blowdryers without a diffuser), prolonged exposure to sunlight, chemical treatments (permanent waves or chemical relaxers), and bleaching or permanent haircoloring. Don’t rub your hair roughly with towels, tie it up tightly every day, use metal barrettes with sharp edges. Avoid brushing or combing vigorously and with force. Do detangle with care, don’t wash hair every day, use dilute shampoos or mild shampoos.
©Science-y Hair Blog 2013
Dealing with high porosity:
What can you do to keep porous hair looking and feeling healthy? Use oils on dry hair or before shampooing to prevent excess water uptake. Coconut oil in particular prevents swelling of hair in water and actually does penetrate into the deeper layers of the cuticle, especially good for porous hair. Try using products containing hydrolyzed protein, or even yogurt for its amino acids, lactic acids and lipids. Keep the amount of time your hair is saturated with water to a minimum. On occasion, massage your scalp gently with your fingertips, then smooth your hands over your hair from scalp to ends like making a ponytail or pigtails to distribute the sebum (there really is no better oil for your hair than that which was meant to be there).
©Science-y Hair Blog 2013

This picture is the end of very long hair and has “seen” a lot of sun – notice that you barely see the cuticle scales. They have fused or been worn away.

To the right -------->
is the same hair, broken at the end.

Below is a less-sun-damaged hair and you can see how the cuticle looked before it was exposed to so much sunlight.

I have treated these hairs with a strong base (potassium hydroxide) which was diluted a great deal (the pH remained at 13) – but still attacked this porous hair shown at left, beginning to dissolve it within minutes whereas the nonporous hair (below, right) was still in fairly good shape (that won’t last long, though). Potassium hydroxide is similar to sodium hydroxide (lye) which is used in hair relaxers. This is a great demonstration of the vulnerability of porous hair and how much more easily things you put on porous hair, penetrate into the cuticle layers, either to attack and cause damage as shown, or to fill in the gaps, soften, and seal in (and out) moisture.©Science-y Hair Blog 2013

Hessefort, YZ, Holland BT, Cloud RW, 2007. True Porosity Measurement of Hair: A New Way to Study Hair Damage Mechanisms. Journal of Cosmetic Science

Chemical and Physical Behavior of Human Hair 
Robbins, 1994. 3rd Ed. Springer-Verlag, New York


  1. Your blog is great!! Being a chemist, I really appreciate it when people spread information actually based on scientific fact.

  2. How can wavy hair be kinky?

    1. Hi Ash, Kinking is a twist of the hair shaft, it's not a curl pattern all by itself. Unless the word "kinky" is being used to refer to a curl pattern, in which case we can't call it "kinking" - but then I don't know what to call it. "Torque" would work pretty well. Think of kinking as a rotation of the hair shaft around its center. Like taking a piece of taffy and twisting it in the middle. Whereas curling of any sort is a rotation around a middle that doesn't actually exist. You can wrap a curl around a toothpick, or a crochet hook, a pencil - to define the diameter of the center of the curl. A wave usually has a curl-shaped center, but it doesn't strictly rotate, it undulates back and forth.