eli5: What is it in “adult” shampoos that makes our eyes hurt and how exactly are kids shampoos formulated to be “eyefriendly”?
In: Chemistry
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.
Latest Answers