I was washing my hair today and, as usual, once I lathered the shampoo into my hair, I let it sit there for a few seconds before rinsing it out.
I acknowledge this is just a habit. But does it make any difference at all? I assume the main ingredient that’s working here is a detergent that’s binding to the oil in my hair and then to the water. Is this pretty much an immediate process or does letting it sit for a few extra seconds cause it to bind to more oil?
What about the other ingredients in the shampoo, like the conditioners, the perfumes, and whatever it is that is supposedly preventing dandruff. Do any of these things have more effect from me letting them sit for some extra time?
I’ve always heard that for shampoo, no, letting it sit does nothing else, but letting conditioner sit for a while does help…i.e. let’s moisture absorb into your hair.
It takes time for the detergent and water to soften and dissolve some substances. Time might also make it remove more natural oil than is ideal also. There’s no one answer to how much time you need, you have to work it out based on the shampoo, your hair and skin, and what gets into your hair.
Think of it this way: shampoo is soap. Quite a bit more gentle than dish soap, but still soap. Now think about doing dishes. Maybe you got a really greasy pan that’s going to be hard to clean. You soak it in soap and water, and the longer you soak it, the more oil comes off. Shampoo, being soap, is going to work the same way.
This is true, and, chemically, shampoo is similar to dish soap (though, considerably more gentle, as @armedmonkey notes).
Those of us who are old enough to remember advertising for Zest “soap” may remember that their ads talked about how it didn’t leave a residue, because “it’s not soap.” Zest (at least, the version that was in a bar) was essentially shampoo (or dish soap) in solid form.
How much time does the shampoo spend on your hair during the lathering vs. how long you let it sit? I think, with little formal reason to, I admit, that whatever process lets the shampoo pick up more stuff while just sitting is much slower than what happens when you mechanically push it into contact with fresh oil and dirt. Skip letting it sit and use half of the time saved for continued rubbing of your scalp and you will have both saved some time and improved the effect of the shampoo.
They told us in janitor school that detergent takes some time to emulsify the oil and dirt so you can go back and pick it up. “Let the chemical do the work,” they’d say. Your head is not a floor, of course, so if you don’t want the shampoo to remove all the natural oils in your hair and scalp, don’t give it any extra “dwell time” for the chemical to work before rinsing it out.
I’ve heard from numerous sources that we tend to over-wash our hair. Some even say that if you’re not in a dirty/dusty environment, then you can get away with not washing it at all, or just rinsing with water. In that case it does take a little time for your hair’s natural oils to reach the right equilibrium, but once they do then it’s pretty stable and not gross. I can’t make that particular leap, but I don’t use much shampoo and never “lather, rinse, repeat” which is a total scam. I do let conditioner sit, like @Omar_Little and don’t worry too much about rinsing every last little bit out either, but I usually only condition when my hair starts getting longer and more unruly, which has been the case during Covid for sure.
A much more effective methodology is to wash it, rinse it, and then wash it again. Letting the first wash “soak” really doesn’t make it more effective.
You ever notice how different that second wash is, if you’ve got really dirty hair? For me it barely lathers on the first go then foams like a mofo on the second. Definitely makes a difference!
I always understood it was one of two things- time AND/OR mechanical agitation. We don’t wash our hands by soaking them in soapy water for a minute, but instead rub them together, which as I understand it helps the soap/detergent (surfactant) basically emulsify the oils/grease so that it can be washed away.
I imagine washing hair is no different- letting it sit for a minute is just going to let the surfactant do its chemical job a little bit more, but that if you’ve already washed it physically, you’ve probably done the vast majority of the work there.
Surely part of the answer depends on how dirty (well, oily) your hair is to begin with. If it is pretty oily, the wait time might matter. If your hair is only a little greasy, then maybe it doesn’t matter.
UNNECESSARY BUT SLIGHTLY RELATED ANECDOTE: I wash my hair every day, despite having heard, like @jjakucyk, that it isn’t necessary. I tried for over a year to cut back, and was careful to use shampoo only every 2-3 days. Since they say it takes time for your body to adjust, I persevered even though I was grossed out by how greasy my hair was. But after about 14 months, I gave up. Some of us are just greaseballs. I guess there are some benefits, as I basically have no crow’s feet.
A few years ago when I was shaving my head, I would wash my scalp before shaving. I used a benzoyl peroxide cleanser as shampoo. The label had a specific wait time, and I could actually feel some tingling going on.
