ged asks...Did your research on hair structure convince you that we do actually need to use shampoo for our hair?
I think shampoo is necessary for most hair types - especially mine, which is very oily - to remove the sebum from our hair. If you look at the way the sebum can cement stuff to our hair and the mechanisms by which shampoos remove those soils, I think it's a very effective and can be very gentle if we do it properly.
I think there are three problems with hair washing - we wash too often, we wash with strong surfactant mixes too often, and we wash all our hair too often.
I know we use all kinds of styling products that necessitate removal, but I think washing every single day is too harsh for most - if not all - hair types. If you do want to wash every day, you'll want to choose a very mild shampoo intended for daily washing with low levels of surfactants with nice emollients and conditioners - a daily use shampoo type product. Sebum is good for our hair, and going a day with slightly oily hair isn't a bad thing both visually and biologically. I think we're really too obsessed with squeaky clean hair.
When you consider that one of the main causes of dry skin is over-cleansing and when you consider how much water we waste with showering, I think skipping a day here or there might not be a bad thing. I know for some people not showering twice a day is an abomination, but unless you're a mud wrestler, how dirty are your arms getting at work every day?
We don't need to wash every single strand of hair on our heads every time we wash our hair. What I've found works well is to wash my scalp well the first time, rinse, then wash my scalp well again. I only wash the rest of my hair very lightly before rinsing the second time. I don't use styling products - well, I use an anti-frizz spray and a leave in conditioner - so I don't have a ton of build-up to remove, but I think this would work well for most hair types. (And I realize that anecdotes don't constitute data, but I've read about this enough times to feel comfortable suggesting it for most hair types.)
Really dry hair can benefit from avoiding shampoo altogether, but most hair types need to remove that sebum regularly. I know some people say that it takes time for our hair to get used to using conditioner only, but I can assure you that an oily haired girl like me would never get used to it. The awful smell of oily hair alone would drive me to the nearest shampoo bottle in a few days!