I just got done reading a thread on DDS (dreaded drag marks) and snorted a noseful of cookie when I tried to chew and laugh at the same time. Nearly did it again on this thread. What a lunch hour!
Anyways, to show what a dinosaur I am, I took one of the last slide rule classes taught at Iowa State. I had to buy a huge Versalog slide rule for the class. (To save the tiny shred of self respect I still have, I won't mention the precise year.) Yes, I was a huge geek in those days -- I confess I put my slide rule holster on my belt because I didn't dare lose or damage it -- no money for any stupidity or frivolity in my undergrad days. And when I did scrape together enough $$ to buy an engineering calculator, it was, of course, a Hewlett Packard, the best I could afford. No self-respecting engineering student bought anything less. It was a major loss of geek points to own a TI (Texas Instruments). And, yes, the calculator case hung on my belt because I didn't dare lose or damage that either.
And, yes, anyways back to soap. Shampoo bars to be specific. I can't speak about the chemistry, but I can speak about my hair.
I make a shampoo/face bar that has zero cleansing and it does a nice job of getting my hair clean without drying my scalp. (For the record, my regular bath soaps have 8 to 12 for a cleansing score, so there's not a huge difference between a face/shampoo bar and a regular bath bar in my house.) Even using a zero cleansing recipe, however, the soap was making my shoulder length, fine hair gradually more harsh feeling and tangly, especially the drier ends. After several months of using shampoo bars, I was about ready to get my hair cut really short to get rid of the dry ends and switch to store-bought shampoo. But I thought, before I did that, I would try the acid rinse thing. It couldn't make matters any worse and (edit) would avoid major fireworks with my dear husband who would prefer my hair to be longer rather than shorter. (end edit)
It really does work. My hair went from rough and dry to much smoother and softer feeling after just a few treatments. I now use my shampoo bars happily, followed by a dollop of hair conditioner (home made of course) that I've dusted with a tiny pinch of dry citric acid powder (canning acidifier, Vitamin C). I let the conditioner/acid do its magic for about a minute and give my hair a thorough rinse.
Vinegar (acetic acid) or lemon juice (citric acid) work as well as dry citric acid powder. I'm just not fond of messing with bottles of vinegar or squeezing lemons. I tried ascorbic acid (Fruit Fresh) but it is not nearly as effective as the others, so I can't recommend it. Regardless of the acid, a little bit is all you need -- too much is just wasteful and the excess acid can irritate the scalp.
I question the idea of ~permanent~ hair damage from shampooing with lye soap. The acid rinse obviously reversed the trend for me without a major haircut needed. Also, my husband with much shorter hair doesn't bother to do an acid rinse. His hair feels fine without it. I'd guess hair that is fine, permed, colored, or not cut often may benefit more than hair that is coarser or is trimmed frequently. But that's just a guess.
You are right, Boyago -- lye soap was the only shampoo in my mother's and grandmother's day, but I also know that gals back then also used vinegar or lemon juice rinses to help their hair stay shiny and soft. So I think there's something to this idea.
