eli5: What is it in “adult” shampoos that makes our eyes hurt and how exactly are kids shampoos formulated to be “eyefriendly”?
In: Chemistry
Soaps that clean well sting. Soaps that clean less well don’t. Kid don’t use any product in their hair and you can get away with the less soapy soaps.
Adult shampoos typically include lauryl sulfates or other harsh formulations to clean your hair well. Kids shampoos use much gentler formulations. These don’t get the oil out as well as adult shampoos, but are mild enough that they don’t cause eye discomfort.
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Baby shampoo has a more neutral pH than adult shampoo. This means it’s more gentle than adult shampoo, which is somewhat alkaline. The pH of baby shampoo is close to the pH of the tears of the eyes so it doesn’t burn because it mimics the pH of tears. Baby shampoo is not very strong cleanser wise, but babies don’t work construction and get all sweaty so they just need a mild soap. Adult shampoo is harsher to remove more dirt and grease.
There was an (apparently incorrect) rumor when I first heard this answered that baby shampoo merely deadened your eye nerves so you just couldn’t feel the ouch though the ouch (damage) was still there. Now, the latest answer I’ve read is that the surfactants in baby shampoo are different than in regular shampoo. Surfactants remove oils because the molecules have one end that likes water and one end that likes oil allowing the oil to be washed away with the shampoo. The surfactants in baby shampoo are longer than in regular shampoos. This makes them less effective, but not as harsh, but since babies aren’t oil factories it works fine.. Sodium lauryl sulfate (C12H25NaO4S) [or (CH3(CH2)11SO4Na)] or sodium laureth sulfate (C14H29NaO5S
or (CH2)11(OCH2CH2)nOSO3Na) are common in regular shampoo, my bottle of baby shampoo has sodium trideceth sulfate which is oddly even harder to find only one formula for but appears to be (C19H39NaO7S). That 39 in the middle kind of shows how long the molecule is.
Edit: redditors who remember more of their Chemistry than I do of my decades old HS classes say the C19 shows the length rather than the H39. Which makes sense as H only attaches on one end and won’t form a chain.
My childhood ended when I realized that “Tear Free Shampoo” bottle I had as a kid (if anyone remembers that) is *TARE* free, not *TEER* free. As in, it won’t tear your hair, it WILL make your eyes tear. Homonym trick.
Chemist here. The molecule most commonly used for cleaning in shampoos is sodium lauryl sulfate (SLS or SDS). If you get that in your eyes or nose it will sting and burn as it not only cleans away dirt but also disrupts the cells.
SLS is perfectly safe to use in body care products for all ages. But to avoid the eye sting other cleaning molecules (surfactants) are used in “no tears” formulations for kids. They are as good for cleaning but don’t disrupt the cells in the sensitive eyes, nose and mouth as much as SLS. The downside is the other surfactants are much more expensive. Also, SLS gives a nice lather that many people like and associate with effective cleaning. (A rich lather is not required to make an effective cleaning product.) The foaming is not as strong with most other molecules, so they require other ingredients to make a nicely lathering shampoo that will make it even more expensive. On a side note, this is why different toothpastes feel so different in your mouth as well – some foam very richly (guess which surfactant they use?) and some do not.
It should be noted that many things in a child’s bath can make the eyes sting even if using gentle products. Just clean water will make your eyes sore, and the relatively low pH in the bath water will also be irritating. However, comparing a standard soap/shampoo with an eye friendly product, the difference is very clear. The sting from the standard shampoo is much worse and stays on for much longer.
J&J’s “No More Tears” meant at first rips and tears, like fraying hair. It’s advertising expanded into tears later.
Should I be using baby shampoo if I have never used any product in my hair before?
No more tears shampoos have nothing to do with soap burning the eyes. It’s a about combing the hair after. There’s no knots or tangles making it pain free to comb.
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