Hi, I'm Craig. Shampoo has come a long way since 1882. Back then, one of the leading shampoos, Slidall's Soap, billed itself as "the soap for all uses," and boy did it stretch that claim. Not only was it marketed as a cleaner for hair and body, but the ads also suggested using it to clean your toilet, laundry, kitchen counters, babies, dogs, harnesses, carriages, and both natural and artificial teeth.

That's just the first of many flaky facts the scientists at Head and Shoulders are helping us clear up. I hope I don't mousse this up. (Laughs) This is going to be bun, I mean fun. 'Cause your hair's in a bun. You know (what I'm talking about).

(Intro)

Shampoos have become way gentler since the 1800s, and the formulas have gotten smarter in the 125 years since then, but why do people even shampoo in the first place? One of the reasons we need the lathery goop is that human scalps are basically waterproof. Glands underneath our skin manufacture sebum, an oily substance that coats hair follicles. In the process, sebum makes hair clump together and appear greasy. But because sebum is so good at waterproofing the hair shafts, a phrase I never thought I'd say, a mere shower or bath won't do much in the way of actually cleansing the scalp. To get past those waterproofed hair shafts, shampoos contain two-phase chemical compounds called surfactants. Half of each surfactant wants to dissolve in water, and the other half wants nothing to do with H₂O. When hair meets water that has interacted with surfactants, it creates a party where everyone is invited, including sebum, dirt, grime, Gary from down the hall... That's what the lather's there for. Not only does it make your head feel like a root-beer float, it washes away clean, taking all the gunk and previously non-water soluble matter with it.

In 1908, New York's biggest paper started publishing columns on how to shampoo the hair. That's because most people in the world didn't know how to shampoo their hair...so that was- that was good of them, giving the people what they need. That's what the media always does...always.

The piece suggested washing your hair once every two weeks, instead of the more common practice of once every 6 weeks. Of course, bathing itself wasn't that popular in history, partially because everyone wanted to act royal, and kings and queens hated taking baths. Louis XIII liked to brag: "I take after my father; I smell of armpits!" Henry VIII could literally be smelled from three rooms away; and Queen Elizabeth I proudly declared that she took a bath once a month, whether she needed to or not...we're guessing she needed to.

How many times a week should you be shampooing? According to experts, two or three times a week is a good rule of thumb. You should also clean your thumb. According to me.

Of course, certain conditions demand more or less shampoo. If you've got Malassezia globosa up there (the scalp fungus that causes dandruff), you might need to scale it up to keep them flakes under control.

Ever wonder why there's silicone in your dandruff shampoo? Polymers like silicone are added to all sorts of shampoos to safely re-coat the hair cuticles after they've been cleaned. The coating smooths them down and adds a lubricating and protective sheath to keep your hair feeling healthy.

Shampoos also get fancy with their polymers; some add volume or weight, or increase the shine and feel, while others protect from things like UV rays. But, in essence, they all work like waterproofing sealant on a deck... don't host barbecues on your hair, okay? ...yowza.

Ever wonder how astronauts wash their hair in space? NASA gives them rinse less shampoo that you simply apply and towel-dry. But the no-fuss shampoo wasn't created in a NASA lab. It was originally developed for hospital patients who couldn't take showers.

But that's not the only shampoo technology invented for the sick: to reduce the burden on nurses and care-workers, Japanese scientists developed a shampoo robot in 2011. The gadget scans the scalp, determines how best to apply pressure to your head, and then works the suds through with its eight magical fingers... (whispers) That's awesome.

It's easy to overlook how much testing goes into many shampoos. According to one scientist, the tools in her lab include a controlled humidity room to analyze whether a new formula will make her hair frizz up; a fragrance center to experiment with how scents are released with water; a special comb that measures the force it takes to de-tangle freshly shampooed wet locks; a friction apparatus that simulates what people feel when they play with the tips of their hair; and a lathering center to determine just how many suds your perfectly calibrated shampoo should have.

The shampoo you get in the US is probably a little different from the same stuff you get in other countries. Shampoo makers adjust their formulas because water quality fluctuates depending on where you live. Hard water, for example, has higher mineral and deposit content that can overwhelm a surfactant. So other chemicals have to be added to the shampoo to counteract the ions that make the surfactants ineffective.

Since the 1960s, scientists have been fascinated with shampoo's fluid dynamics. It was those crazy, free-wheeling, fluid-dynamic 60s.

Like many fluids, shampoo coils up as you pour it on to the surface, and the liquid slowly moves downward. But then, every once in a while, the shampoo stream will bounce up like a rubber ball. Boingg! That uncanny behavior is called the Kayes Effect, and it took scientists about 40 years to explain the mechanism.

You want another strange and wonderful thing about shampoos? Because shampoos are good at breaking down body oils, putting a dab on the inside of your shirt collar can help clear away your greasy collar stains.

Recently, American scientists discovered that by using a tweaked shampoo recipe on old woolly mammoth hair, they could remove the extraneous bacteria from the strands and get clean DNA samples. The discovery has helped them to declare a new species of woolly mammoth, and they're eager to try the shampoo on other museum animals.

I mean, I've been doing that for years, but I got kicked out... I discovered some stuff...I'm not going to tell you about it, though.
Finally, I return to the salon to tell you that baby shampoos are just shampoos that use milder surfactants, and don't have special polymers or moisturizing agents, as a matter of..surfact. (Laughs) Baby glands create sebum at a much lower pace than adults, so their hair is less oily and greasy. Also they're wittle babies who have no say in what their parents put in their hair...so the joke's on them. Ha! You got no options, kid.

Thanks for watching Mental Floss on YouTube, made with the help of these flaky people. And thanks again to Head & Shoulders for helping us make this episode possible. And to Sofia Vergara, whose flake less, flowing hair was an inspiration for every single fact in this episode-- except the one about baby shampoo...that was inspired by a dandruff-free baby...of...a random one...you know which one you are.