It's fairly common to have hair that is porous on the ends, but not at the roots. That means different parts or your hair require rather different care. How easily your hair becomes porous with just normal wear and tear and weathering depends on a lot of things. In fact, the kind of porosity your hair accumulates can be very different from person to person.
How can the ends of your hair become porous? The ends of your hair are the oldest - they have had the most time to accumulate damage. While you up to 11 layers of cuticles covering your hair, if your hair is long there may be few layers left on the ends. Brushing, combing, detangling, sleeping, wearing hats and collars, blowing around in the wind, wearing ponytails and braids and barrettes; these activities cause cuticles to chip or break away completely. Even more dramatic is over-washing the hair (especially if using strong or concentrated detergents), bleaching, highlighting or lightening the hair, permanent dyeing the hair (when they dye includes ammonia and/or peroxide), chemically relaxing or permanent waving the hair. Spending lots of time in the sun causes cuticles to shrink so they cover less area. Using high heat hair styling tools can cause cracks that increase porosity.
Hair that curls or has kinking (or both) "wears" or weathers more unevenly than straight hair because there are certain areas which accumulate more friction than others, so it is more likely to become porous. Anything that sticks out can be broken off easily - and that goes for cuticles on your hair where it kinks and curls.
Fine and medium hair is more flexible than coarse hair and tends to become porous more easily because it bends around things (like other hairs) readily and therefore accumulates more surface-contact with objects and that means more friction!
What's the problem with porous hair?
Porous hair loses water more quickly than low porosity hair. Think of the function of the cuticle of low porosity hair as a plastic bag. Not very porous. Water doesn't get in or out easily. But if you punch holes in a plastic bag or rip tiny cracks, water can get through. When your hair is porous, water gets in and out easily. So when you put your hair in water, it takes on water and swells. Swelling is bad for hair because it creates stress within the hair. When porous hair gets wet, it can lose soluble proteins to the water. Bad news - because those proteins in the outer portions of your hair help keep it hydrated. When porous hair is dry (dry meaning not wet), because it has no tight barrier against the environment, so it can lose more moisture than is good for it when the air around the hair is drier than the hair itself.
Hair may grow out of your scalp with low porosity. It may not stay that way for long, depending on what you do to it and what your hair is like. For whatever reason hair becomes porous, porous hair becomes dehydrated easily and dehydrated hair is more brittle and prone to breakage, less shiny, does not hold a curl as well, frizzes easily.
What to do
Low porosity hair is water-repelling. Not as much as the back of a duck - but it does not swell with water quickly when wetted and it does not lose water very readily to the environment around it when dry. Because normal-porosity hair is so resilient to the environment, and because it tends to stay resilient, it's a good idea to encourage more-porous hair to act like less-porous hair. Water-repellant hair does not swell in water, accumulating more stress and more damage. It resists damage. It does not become dehydrated quickly! It does not absorb humidity rapidly and frizz immediately. We want our hair to repel water somewhat.
If your hair is porous on the lower portion, what can you do to balance out your hair's porosity?
- Pre-shampoo (pre-cleansing) oil treatments on the porous areas - ends and probably the top layer too. Especially with oils like coconut, sunflower, grapeseed, avocado or olive oil. Enough oil to add shine - or enough to make your hair look greasy - that's up to you. Oils will repel water during cleansing to prevent the swelling that can cause further damage. You'll know you used the right amount when your hair, post-washing does not look frizzed out and extra-poofy, nor greasy and lank when dry. If just your ends are porous - use this treatment only in those places.
- Condition-wash-condition. Pre-shampoo conditioning also buffers hair from shampoo and water, but conditioners can build up in a way that liquid oils do not. If the idea of using oils in your hair make you say "yuck," this method can give you wonderful results. The conditioner before washing can be applied to wet or dry hair.
- Use shampoo, conditioner or styling products which contain proteins or amino acids or film-forming humectants. This link has a list of products based on film forming humectants. Proteins and amino acids are hydrating to hair and can help hair that tends to be dehydrated, hold on to moisture. Film forming humectants (flaxseed gel, okra gel, aloe vera gel, pectin, celluloses) are not especially affected by ambient humidity and can seal in moisture all day to keep porous hair hydrated.
How can you prevent your hair from becoming porous?
- Comb, don't brush. Or skip the comb entirely and just use your fingers. Brushes are great for shredding cuticles of your hair! A wide-tooth comb will get the job done. If you have tangly hair, detangle starting with your fingers, then a wide-tooth comb and work from the ends, up. Don't tug or yank on hair! Once you over-stretch a hair, it's damaged forever.
- Use ammonia-free and peroxide-free or low-peroxide, semi-permanent hair dye or plant dyes like henna.
- Shampoo only when your hair needs it. Switch to "sulfate free" shampoo or dilute your shampoo to make it more gentle to the hair.
- Use lower-heat hair styling tools.
- If fabric touches your hair and your hair becomes porous easily - make sure it's silk or satin or at least slippery-feeling fabric.
- If you use henna in your hair - make sure it has plenty of lubrication because henna increases friction in hair.