See part 1 of 2: Porosity- Definitions and Causes
Now that we know how porosity occurs I can now take on your burning questions
Q: Can all porosity be fixed
No, when the cuticle sustains damage, this simply cannot be fixed. The cuticle does naturally thin down as hair length increases due to normal weathering (Journal of the Society of Cosmetic Chemists pg155-175, 1977). Broken, chipped or missing cuticles and cracks in the hair cannot be permanently fixed. Using hydrolysed protein can temporarily improve the hair but ultimately this is temporary.
Q: Can you open and close the cuticles of the hair?
This is NOT (I repeat NOT) the way the hair cuticle works. It does seem to imply that the cuticle is hinged like a door and can be raised without damage and then ‘closed’ back down. However this is not how it works.
The cuticle can be raised slightly (it takes very sensitive instruments to detect this – the distance can be as little as one millionth of a meter). Running your fingers down a strand to feel for a raised cuticle is simply not possible unless you have severely damaged hair.
Q: Can you stop the cuticle from being raised?
Not really because you have to wet your hair and handle it on occasion. You can however take steps to keep it to a minimum
1. Coconut oil as a pre-wash treatment to prevent the hair shaft from swelling. This in turn may help the cuticle from being raised (search this blog for coconut oil posts)
2. Using a conditioning shampoo. This in research terms means the dreaded term silicones which although loathed by many curly heads really actually are good for minimizing protein loss from hair (meaning chipping/breaking cuticles) (Journal of the Society of Cosmetic Chemists, pg 39-52, 1995). If you are anti-silicone, pick a conditioning shampoo (key word conditioning)
3. Hair conditioner use after shampooing has been shown to restore the hair fibre appearance (meaning smooth down the cuticle after shampooing) (Journal of the Society of Cosmetic Chemists, pg 347-371,1993). It also helps with combing and reducing damage to the cuticle during this process (see this post)
Q: Does apple cider vinegar help to ‘close’ the cuticle?
There is no evidence to support that pH (i.e low pH of ACV) can affect the hair cuticle in this way. High pH (9 and over) found during relaxing can raise the cuticle and even destroy the hair completely (J Invest Dermatol 105: 96-99, 1995). This study did also show that hair did not show any real change, meaning the cuticle was not raised or smoothened by exposure to a large range of pH values (about pH 4 to 8).
Q: Does cold water help to ‘close’ the cuticle?
Again there is no evidence to indicate this happens. Heat, even low heat with a blow dryer (70 degrees Celsius for 30 seconds) does raise the cuticle. You can see it for yourself in this paper which has a rather excellent image –see figure 4.
There is no evidence that I could find that running cool/cold water over the hair impacts the cuticle in any way.