Considering that all shampoos do the same thing (clean hair), there are enormous price disparities between products. Some cost as little as 4 cents per ounce, others 100 times as much. And there are customers to support all prices along the spectrum.
"There are good and bad products at all price ranges," said Paula Begoun, author of "Don't Go Shopping for Hair-Care Products Without Me." "Expensive doesn't mean better, and price is not indicative of quality. There's only so many ingredients that clean hair, and the ingredients that clean hair are the same regardless of price tag."
Although some shampoos come with long ingredient lists that extend along the entire vertical length of the bottle, "there's only six or seven that make any difference at all," said Perry Romanowski, a former cosmetic chemist who contributes to the blog the Beauty Brainshttp://thebeautybrains.com/whoare/.
The most abundant ingredient in any shampoo is water, he said, which helps dilute the remaining ingredients so the shampoo can be spread through the hair. In addition, shampoos typically contain detergents, most likely lauryl and laureth sulfates. Those are the chemicals, or surfactants, that foam and clean the hair of oil, dirt and whatever styling products may have been used. Of the two, lauryl sulfate is more cleansing — and possibly more damaging and drying to color-treated hair in particular because it so effectively strips the hair of whatever's coating it.
Conditioners such as dimethicone and other silicones and moisturizers (for example, panthenol) are also on the ingredient list because cleaning the hair also dries it out and makes it difficult to comb. Then there's salt, which often shows up on labels as sodium chloride and helps thicken the formula; preservatives, including DMDM hydantoin and methylparaben, that prevent mold, bacteria or fungi from growing in the product; and aesthetic ingredients that characterize a shampoo's foam and color and how it smells — subjective add-ins that play to the psychology of the user.
A thick shampoo is associated with expensive, luxury brands, such as Pureology. A thinner, deep-cleaning product will generally spread through the hair more easily, like Neutrogena. A moisturizing shampoo like Nexxus Therappe is typically creamy, almost as if there's lotion in the hair.
It isn't so much the active ingredients that vary from product to product but, rather, their ratios, which are altered to accommodate hair types — oily or dry, curly or straight, color-treated or natural. And while a major trend is afoot to replace sulfates with milder cleaning agents and to use so-called natural ingredients, most of the ingredients in shampoos, even if they are plant-derived, are processed in a lab.
And what about tap water? Romanowski said the minerals in it have no effect on shampoo, despite a common perception that shampoo performs differently if the water is hard or soft. "If shampoos were based on soaps, that would be true, but they're based on detergents," which are chemically different, he said. "We've researched this and we haven't been able to reproduce what people claim."
As for trendy ingredients, such as awapuhi, ojon and argan oil, even hemp, there's too little of it in any product to make a difference, many shampoo experts say.
Yet that doesn't stop shampoo makers from touting their perceived benefits, or consumers from buying in.
Psychology is driving at least part of the market for higher-end shampoos in particular, according to Karen Grant of the New York-based market research firm NPD Group.
"If customers feel they can replicate a salon treatment at home, they are more likely to invest in a high-end shampoo," Grant said. "Instead of spending $50 to $100 in one sitting at a salon, they buy a higher-grade shampoo hoping they can extend the time in between" visits.
"Shampoo is very subjective," said R. Randall Wickett, professor of pharmaceutics and cosmetic science at the University of Cincinnati. "Of all the products you use, it's the one you interact with most intimately. You pour it in your hand, put it on your scalp, rub it through your hair. You're smelling it, feeling it, feeling how it feels when you rinse it off.
"The bottom line is people have been making shampoos a long time and they know how to do it and there's a lot of varieties and people should find what they like. You don't need to spend $50 for a bottle," added Wickett, who uses "whatever shampoo my wife buys and puts in the shower."