[powersnail]

> No; you would need to touch people hair after a shampoo shower and after a non shampoo shower to see the difference.

Yes, that's exactly what I mean. My girl friend has long hair, and doesn't wash with shampoo every day (which is somewhat common for long-haired people I believe), and the texture after shower is very different.

In college, especially exam week, we had more anecdata. It was possible to see people who 1) had not washed their hair, 2) had washed their hair in a sink with water only, 3) dry-washed with those sprays, and 4) washed with shampoo. It was very easy to tell which they did.

In general, soapy cleaner (or similar substances) is going to help immensely when cleaning oily stuff. And hair can be really oily. Water-only is just not the same.

One scenario I don't have is comparing other soapy products to shampoo. But shampoo aren't more expensive than other soaps anyway, so I never bothered to look.

[degamad]

> doesn't wash with shampoo every day

There are two types of people who don't shampoo every day: those who don't wash their hair every day, and those who wash their hair with water most days but shampoo only some days.

If your girlfriend is in group 2, then your experience is relevant to the parent's post; if she is in group 1, then you haven't yet experienced the difference.

[OneDeuxTriSeiGo]

I'm in both group 1 and 2 (I normally alternate between the two, i.e. soap - water - soap - no wash - soap...).

Washing with soap removes oils. This is a pretty obvious effect from anyone who's ever tried to clean up oil/grease with soap (ex: dawn).

Rinsing with just hot water distributes oils from the scalp down towards the ends and it removes a little bit of oil in the process.

Rinsing with cooler water is less effective at distributing oils but also loses less oil in the process.

Not washing allows grease/oils (and skin/dander) to build up on the scalp and saturate hair near the scalp.

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If you are just rinsing/scrubbing with water, it does a lot relative to not washing at all but there isn't really a comparison when it comes to soap's efficacy at stripping oils/making them semi-water soluble so they can be washed away.

[powersnail]

To clarify: in that anecdote, I'm talking about washing hair in shower, with hot water, with no shampoo.