Going shampoo-free: a question for the chemists

[serenissima]

I've been doing the no-shampoo thing for about a month.  I cut my hair boyishly short over the summer, and I thought it was a good opportunity to try this method of cleaning my hair with baking soda solution and apple cider vinegar solution.  I was a little apprehensive about the baking soda and used only two teaspoons instead of three teaspoons (one tablespoon) dissolved in eight ounces of water.  What I found is that this proportion is very mild for me, and after a couple weeks I stopped using the apple cider vinegar.  I've been washing my hair once or twice a week, applying the baking soda solution to my crown and then rinsing out, and the only difference I can tell from when I used shampoo and conditioner is that it takes longer for my hair to get greasy, hence the infrequent washing.  (The bigger difference was from cutting my hair short: it reduced my time in the shower by around 66%.)  So, I'm sold.

The puzzling thing, though, is that the baking soda solution actually lathers up a little bit as I scrub it into my hair.  I see suds.  What causes that?  There are no suds in the bottle.  Is the baking soda reacting with my hair oil?