1. pH alone is NOT enough to relax hair
Sodium hydroxide at a pH of 13 but at a low concentration actually DOES NOT relax hair (J Soc Cosmet Chem, pg 347-352, 1994). Relaxing hair is more complex than just pH alone. If you are curious about the necessary factors then see my previous post on the subject - here
Also we should consider other evidence.
1. I did an experiment with shed hair and the hair did not change in appearance despite the pH of 9 - see it here
2. Roshini of Glamazini as well as her husband are long time users of castile soap and they have a lot of beautiful natural hair between them. (Yes I know she is on the hunt for shampoo now but castile soap has certainly done no harm to her mane!).
3. Sera of Sera252 mentioned that she cleaned her braids with baking soda, she is clearly natural with a full head of hair.
2. Can castile soap or baking soda use damage hair?
From the previous post we know that the hair cuticle is not really perturbed by the pH range of 4-9. In my personal opinion, I do think that pH 9 is quite high and I do think it is wise to stick to the mild acid to neutral range (i.e 5-7). However, it does appear that hair is pretty resistant to acid or base.
3. Do castile soap or baking soda remove silicone?
Non water soluble silicones are pretty hard to remove. There is research on use of SLS but not soap or baking soda. This is because soap is not considered a sophisticated ingredient (yes really scientists do say this). SLS actually does not entirely rid a surface of silicone but will remove the vast majority of it.
Soap does dissolve oil and probably will to some extent dissolve silicones but SLS does it better. Baking soda is known as a scourer (i.e scratch clean) rather than an oil dissolver, so I do not think it would be effective (Please note, there is no research to support this, it is my scientific opinion).
4. Should you switch to shampoo?
I am a huge proponent of manufactured products specifically shampoo and conditioner (especially from companies who actually have research labs). Ultimately I think that everyone has to work with what they are comfortable with and if you prefer shampoo bars or castile soap or baking soda and have had no problems so far, then there is no issue with sticking to what you like.
I hope this series helps those of you who wanted these questions answered. I hope you can also find a happy medium with your product choices...........I'm off to skate!