We know such a fairy tale about "does not pinch his eyes"!
When I was little, I fell for it.
Mom bought baby shampoo "Drakosha" (I wonder if they sell this now?). It smelled like strawberries, and on the packaging it was written in red and white: "No tears."
Well, what am I? I can't do without experiments! We already ate soap at our 8 years old, liquid for washing dishes instead of foam for a bath was poured into the water, now it was the turn of the shampoo "No Tears".
I poured a little of this shampoo into my palm and slapped my eye, as if I'd have a mosquito in my eye.
It stung awfully!
Plus, baby shampoos have a neutral environment (pH = 7, amphoteric surfactants remain soluble in any reaction of the environment), contain less salts and, accordingly, draw less water from the eye (isotonic solution).
Simply put, the molecules of soap, shampoo and other surfactants are structured as follows. They consist of two ends - hydrophilic and hydrophobic. The hydrophilic end is attracted to water, while the hydrophobic end is attracted to fat. When you wash your hands and hair, surfactant molecules combine with fat on your skin and hair. And when you wash off, these molecules at the other end combine with water and are carried away by it, capturing particles of fat. And the fat, in turn, carries away the particles of dirt that sticks to it.
Why does shampoo and soap sting your eyes? The surface of the eye is protected by a tear film. It contains fats in its composition. When the shampoo enters the eyes, its molecules combine with the fats in the tear film and carry it out of the eye. The surface of the eye is exposed and is even more exposed to surfactants. They are embedded in the tissue and irritate the nerve endings - a burning sensation is felt.
Baby shampoos without tears have a special composition of their molecules. They contain amphoteric surfactants. The molecules of such surfactants are much larger and therefore cannot penetrate the eye tissue, although they wash away the tear film. Also, baby shampoos may contain anesthetics (to reduce the burning sensation). The disadvantage of these shampoos is the high price and insufficient foaming.