Q1: Does pH raise or close cuticles?
There are two authoritative studies on this with pretty similar results. There is very little change to hair structure between the pH ranges of 4 to 9. Hair protein resists changes due to acid or base. Tests were performed using hydrochloric acid (powerful acid) and sodium hydroxide (a strong base).
1. Hair does not absorb noticeable amounts of acid or base between pH 4-10 ( J Soc Cosmet Chem, pp 393-405, 1981)
2. The cuticle separation distance is within the same range between pH 4 -9 (J Invest Dermatol 105: pp96-99, 1995)
Q2: Do the cuticles not open at high pH?
I insist on using correct terminology. The cuticle is not a door that can open and close. It is a protein whose structure can be affected causing it to lift. Yes the cuticle does lift around a pH of 10.
Q3: Are you really saying that hydrochloric acid and sodium hydroxide really do not affect hair?
In the range of pH 4 to 9 yes, there is not much change to hair. In fact soaking hair in water (yep plain ole water) for a long time (circa 10 minutes is long) actually yields greater change to the step height (see above) than acid or base.
Q4: What happens outside the pH 4 to 9 range?
At both low and high pH there appear to be structural changes to hair causing it to become more dense. This is thought to be a result of the acid or base changing the protein.Very high pH can actually dissolve hair.
1. How long does it take skin/hair to 'recover' from alkaline pH
2. Does pH affect anything else (hint: bacteria and fungi)
3. Is pH sufficient to relax hair?
4. Q&A regarding use of castile soap and baking soda - should you really use them?
See the related post courtesy of a reader's question - http://thenaturalhaven.blogspot.com/2010/07/does-hair-really-not-react-in-ph-range.html