The Truth About Shampoo

Ever wonder whether you really need shampoo? How does it work—and is there any reason to pay big bucks for the expensive brands? We did the research.

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When was the last time you sat down and thought about shampoo?

We’re not talking about spending 20 minutes browsing through bottles of TRESemmé during a shopping trip. We’re talking about the actual function of shampoo itself. Why is it necessary? Is it really necessary? And is there really any difference between the pricey products lining the walls of your favorite salon and, say, the cost-effective options at the drugstore? Or a bar of soap?

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We’ve been thinking about shampoo for a long time now—probably too long, according to our friends and family—so we decided to reach out to a few experts to get some answers.

First of all, what does shampoo actually do?

You can probably guess the basics, but to really answer some of the difficult questions about shampoo, it’s important to understand how it works.

“[Shampoos remove] two things: the natural oil that accumulates in the hair and dirt from the environment,” explains Laura Waters, PhD, principal enterprise fellow at the University of Huddersfield. Waters is a forensic anthropologist who studied shampoo for BBC Two‘s Horizon.

Dermatologist Fayne Frey, MD, gets a little more specific in an email to HealthWay: “Shampoo is basically a liquid cleanser designed to clean the scalp of sebum, sweat, desquamating skin cells, styling products, and dirt.”

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Desquamation is the clinical term for when skin sheds (it’s also our new favorite word). Sebum is the oil our skin naturally secretes.

Basically, shampoo works in exactly the same manner as bar soap: It uses detergents to get rid of oils. The detergents are the heavy lifters, and other ingredients thicken the shampoo (watery shampoos don’t sell well), prevent bacterial contamination, add a pleasant smell, and make the mixture foam up in the shower.

“… well-formulated shampoos will clean the hair adequately and leave the hair aesthetically pleasing to the consumer. The trick is finding one you like.”
—Fayne Frey, PhD

People respond to that foaming action, but foaminess doesn’t guarantee cleaning power.

“Most consumers think foaming equals cleansing, although the two are not related,” Fayne clarifies. “Almost all shampoos are built around detergents that are blended together to achieve the [optimal] amount of cleansing, depending on the type of hair.”

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“Harsher detergents, or surfactants, strip the hair of almost everything,” Fayne continues, “leaving the hair dull and lackluster, often [susceptible to] static electricity,” she explains. “Milder surfactants don’t clean as well but leave the hair more manageable. Certain ingredients are added to shampoos to address manageability, and other ingredients are added to make the shampoo itself more appealing to the consumer.”

What about specialty shampoos?

Specialty shampoos are big business. Baby shampoos, for instance, promise “no tears,” while oil control shampoos promise to detoxify the scalp and reduce grease. That’s not all marketing, but it doesn’t imply any massive differences in the formula’s basic composition, either.

“There are many different ‘types’ of shampoo claiming to be for different groups of the population,” Waters says. “They all do the same job—clean your hair. It is just that some, such as baby products, use milder [or more dilute] surfactants, which means they will be less likely to irritate the skin but also not be as effective if you have a lot of oil/dirt to wash away.”

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“Most of the other types of shampoos, such as ‘volumising’ and that sort of thing, have added ingredients as well as the surfactants,” she says. “Some put a coating on the hair to make it seem thicker, some have extra conditioners, but they still all contain surfactants.”

That’s also true for bar soaps. In fact, if you find yourself in a situation where you’re completely out of shampoo, a little bit of bar soap should accomplish the same basic thing.

That’s right; shampoo is, ultimately, unnecessary. That doesn’t mean that it doesn’t serve an important purpose.

“Most people believe that their hair looks better when the oil is removed,” Waters writes. “It looks and feels cleaner, but there is no need to wash it away, really.”

That brings us to the “no-poo” movement.

Disregard the silly name; the idea is that hair is healthier without shampoo because the natural oils in our hair are, well, natural. Why strip away something that’s supposed to be there?

It’s not a ridiculous idea, and it’s gone somewhat mainstream. Gwyneth Paltrow is an avid no-poo-er, per a report in Express.co.uk, and publications like Marie Claire and The Telegraph have published fawning testimonials from no-poo adherents.

There’s even a dedicated site, nopoomethod.com, to guide new non-users. According to Frey, there’s nothing wrong with foregoing shampoo completely, provided that you don’t mind some changes in the texture and feel of your hair.

“For healthy scalps, personal preference [determines how often you should shampoo],” she says. “[There’s] no consensus. No evidence that shampooing at any given interval is beneficial to scalp health.”

If you don’t wash your hair at all, sebum will build up, potentially causing itchiness or oily dandruff. With that said, Frey notes that scalp health and hair aesthetics are two entirely separate issues.

“Individuals with scalp conditions, redness, itchy scalp, scaly scalp, or other irritations should seek medical attention and see a dermatologist before expecting to cure their scalp ailments with [over-the-counter] shampoos and conditioners,” she says.

We asked Frey whether our shampoo habits might harm the health of our hair.

“The bottles say lather, rinse, repeat, but they never tell you when to stop!” says Frey.

We’ll always appreciate a decent shampoo joke.

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“The answer to your question is there is no consensus on how often [to shampoo] or if any given individual with a healthy scalp really needs to shampoo,” she explains. “Before the 1930s, shampoo didn’t even exist. Folks used bar soap if they desired to clean their hair.”

The first liquid shampoo hit markets some time around 1927, but of course, people had been washing their hair for centuries prior. Modern shampoo is largely safe; cosmetic shampoos are regulated, for both their contents and their branding, by the Food and Drug Administration. Medicated shampoos must be approved by the administration.

That means those scary-sounding sulfates listed on the back of your shampoo bottle are safe—within limits. One study published in the International Journal of Cosmetic Science did find that sodium lauryl sulphate, a common commercial shampoo ingredient, caused noticeable damage to hair proteins. That study was carried out at a microscopic level, however, and the authors didn’t recommend against shampoo use; their goal was simply to compare the conditioning effects of different hair products.

Frey says that, provided you have a healthy scalp, you can shampoo your hair as frequently or infrequently as you’d like.

“Folks who don’t want to expose themselves to the chemical ingredients in shampoos … never need to shampoo,” she tells us. “Shampooing daily has become part of the American culture, but for most [is] totally unnecessary. Some say it is un-American to not shampoo, but the ‘no-poo’ movement is growing.”

For what it’s worth, we couldn’t find anyone who says that it’s unpatriotic to forego shampoo, but we’ll take Frey’s word for it. The takeaway is that if you like oily hair, you can safely stop shampooing. Just be prepared for the results.

“It is perfectly normal to have oily hair, but most prefer not to … . [How] quickly your hair generates oil depends on how often you need to wash it away,” Waters says. “Dirt from the environment sticks to the oil, and so the former makes the latter seem worse.”

Ever thought about pH levels? Maybe you should.

“Certain characteristics of shampoos and conditioners will affect hair appearance,” Frey notes. “The pH of a shampoo can affect [hair strength] and manageability. Unfortunately, the pH of … shampoos and conditioners is not found on the labels. Consumers must contact the manufacturers for this information.”

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“The pH of the scalp is around 5.5; pH of a hair shaft is around 3.6,” Frey continues. “Very alkaline products (high pH) can leave the hair with static and difficult to manage.”

According to one study in the International Journal of Trichology, shampoos with an alkaline pH may “increase the negative electrical charge of the hair fiber surface and, therefore, increase friction between the fibers.” That friction, in turn, could lead to cuticle damage fiber breakage.

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While the researchers advocate for pH labeling on shampoo bottles, they acknowledge that further research is needed to figure out what the optimum pH range is.

Our experts agreed on one point: Great conditioners, it seems, are worth the money.

When we asked Frey whether shampoos can ever really add volume to hair, she quickly got to the real issue.

“Possibly, for some people, it can appear to have a small effect for the short term,” she writes. “[But] it’s the conditioner that makes a much bigger difference.”

“The idea of beautifying the hair is a secondary issue for shampoos and better addressed by well-formulated conditioners,” Frey says.

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Conditioners basically bind cuticle flakes to the shaft of each hair, providing a smooth feel and improving appearance. They’re not magical—they can’t add new hairs to your head, either—but they can provide the so-called “volumizing” effect that manufacturers love to tout.

“Shampoo doesn’t tend to be left on the hair for long and is quickly washed away, whereas conditioning products are left on for longer and more likely to have an effect,” Waters says.

“The price of a shampoo is only partially about the ingredients: it is also the image, such as the packaging, et cetera,” Waters continues. “… I wouldn’t buy the [expensive bottle of] shampoo, as it isn’t that much better than [an inexpensive] bottle.”

“Some like their hair a bit wavy, others not so much. Beauty, when it comes to hair, is truly in the eyes of the beholder.”

—Fayne Frey, PhD

Frey recommends experimenting to find what works well with your hair and scalp.  

“Of course, well-formulated shampoos will clean the hair adequately and leave the hair aesthetically pleasing to the consumer,” Frey says. “The trick is finding one you like.”

When buying any product for your hair, it’s imperative to keep that you in mind.

“Some folks like the full, wild hair look, others prefer flat,” Frey says. “Some like their hair a bit wavy, others not so much. Beauty, when it comes to hair, is truly in the eyes of the beholder.”

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