Here is my question !
I wonder why some shampoos (anti-dandruff, and bought in drugstores) only foam after a first application and rinsing, but never on first application. :dubious:
It doesn’t happen with other shampoos (cheaper and probably less effective) that you buy in supermarkets. First application, it foams !
I’m not sure I will understand your answers if it’s too scientific, but please answer if you know why !
Dirt and oils in the hair on the first shampoo application stop foaming to some degree in all shampoos. It’s just more noticeable in dandruff shampoos because they don’t foam up as much as other shampoos.
Or
Dandruff shampoos have as much foaming abilities as other shampoos, but since they have additives that break down sebum better than regular shampoos, they foam less.
All shampoos do that for me but my hair is thick and somewhat oily. The first pass gets it clean enough so that the shampoo can bubble the next time. I don’t usually choose a next time because seeing bubbled isn’t that important to me but I know the drill. I would assume your particular hair just makes this a slightly different variation on it.
I don’t lather, rinse, repeat, and I’ve never noticed any shampoo not lather up first time…
Well, you must bathe regularly or something. 
I sometimes wash my hair everyday, and no matter what kind of shampoo I use, it never lathers well on the first wash.
How well a shampoo lathers also depends heavily on how hard the water is. With really soft water, it is likely to lather on the first use for most people.