saponification during which oils and a very alkaline thing like sodium or potassium hydroxide are mixed together to create a soap. We can't extrapolate this to mean that every alkaline and every oil will mix to create a soap. Lye works because it's very alkaline - over 13 - and baking soda is pH 8 to 9.
Try this at home! Dissolve some baking soda in a small amount of water. (Acid and base reactions require water to create an aqueous solution.) Then add it - let's say 1 tsp - to something like 1 tbsp oil. Mix and mix and mix. You will not get soap. You could do equal amounts of 1 tsp baking soda and 1 tsp oil and you won't see a soap. (The same thing with boric acid - it's an acid, so it's not going to create a soap on its own.) If this were the case, why wouldn't we just throw some baking soda into our batch of oily dishes and create our own dishwashing liquid? It would be so much easier, cheaper, and better for the environment.
You cannot saponify the oils in your hair with baking soda. The pH of baking soda isn't great enough to create a soap. If you don't believe me, try the experiment above. It's okay if you like washing your hair with baking soda, but this is not the mechanism by which it might be working for you.
If you combine a strong acid and a strong base in equal amounts, you'll get a pH around 7. If you combine a strong acid and a weak base in equal amounts, you'll get a pH in the acidic range (and one that might not change at all, depending upon how weak your base). If you combine a strong base and a weak acid in equal amounts, you'll get a pH in the alkaline range (if it changes at all). If you combine a weak base and a weak acid, you'll have to do some work to see what you get. This is called a neutralization reaction, but it doesn't mean the end result is pH 7.
Besides, neutralizing something to pH 7 isn't a good thing. Let's say you have just enough of an alkaline thing and just enough of an acidic thing to get you to pH 7, is that really the best thing for that body part? If your skin is intended to be pH 4.5 to 5.5, neutralizing it to 7 is going to cause you great pain and misery. If your hair is intended to be pH 3.5 to 6, getting it to 7 is going to cause all kinds of cuticle lifting and damage.
The CEO of my pharmacy wrote an article in his company coupon book/newsletter a few weeks ago in which he stated that we could tell shampoo was toxic because it makes our eyes water. This is silly! The reason our eyes water near shampoo is because they have a pH of about 7.4 and body wash, facial cleanser, shampoo, and so on are around pH 4.5 to 6, which means they aren't similar pH levels. If we put coffee, baking soda, or orange juice in our eyes - natural and non-toxic things - you'll experience eye watering. If you get sand or an eyelash in your eye, we'll have watery eyes because of irritation.
And I'm sure you've seen the alkaline water stuff around. (I'm not linking to it because I don't want to give it more promotion.) Everything they say is pretty much untrue. Think about this - if you have gastric acid in your stomach (pH 1.5 to 3.5, so it could be considered a strong acid at 1.5 - reference) and you add weakly alkaline water to it, what's going to happen? (Strong acid plus weak base equals acidic pH levels.) Will the pH of your stomach change? And how can it possibly get to any other part of your body when it hasn't changed your stomach pH by a tiny bit? There's nothing of this alkaline water left mere seconds after you ingest it! And don't get me started on the idea of microclustering!
I'm not saying you need to take a degree in chemistry, but a little good and correct knowledge can be a powerful thing when you're assessing claims about products or processes! Do you have a question about a chemistry claim? Send it to me!
Chemistry Thursday: Let's take a look at pH
Chemistry Thursday: How to measure pH
pH and our skin care products
An aside: pH and lotions
A few thoughts for the day: ...pH of our bodies
pH and bath products
Neutralization reactions (Wikipedia)
Neutralization reactions (Elmhurst University)