Why doesn't tear-free shampoo sting your eyes?

What's in that shampoo that keeps baby's eyes from stinging? It's more like, what's not in that shampoo?
What's in that shampoo that keeps baby's eyes from stinging? It's more like, what's not in that shampoo?
Peter Oshkai/Flckr/Getty Images

It's time for baby's bath, and everything is perfect. The water's lukewarm, the hooded bath towel awaits and the specially formulated baby shampoo is close at hand.

While baby doesn't have Rapunzel-like tresses to shampoo, those three hairs on the top of her head still deserve a good cleaning. And within minutes you've worked them into an impressive lather, thanks to the lavender-scented baby shampoo you picked up at the market.

Just as you're about to congratulate yourself for successfully cleaning a miniature person with all the helpfulness of a wet noodle, panic strikes. A river of shampoo bubbles are making a break for it, leaving the crown of her head for the hills and dales of her eyebrows and -- oh no! -- her eyes. Before you can react, she blinks, sending suds marching across her corneas. And smiles.

She smiles? Where is the howl-inducing sting that comes with shampoo in the eyes? And then it hits you. This is baby shampoo. Tear-free. No tears. A sans howling formulation.

Although you're struck by a sense of relief, you begin to wonder: Why doesn't this shampoo sting her eyes? An adult formulation certainly would (you know that from experience), so why not the baby version?

Odds are, if you were to pose this question at your baby's next playdate at least one person would tell you the secret behind the "no tears" formula: It contains all the eye-stinging chemicals as adult shampoos, plus a desensitizing agent -- Novocain, lidocaine -- to numb the eyes.

Which makes scary sense, except for the fact that it's false. Baby shampoos don't contain anesthetics. If they did, your hands would feel number after washing baby's hair. And babies and children using the products would be at risk for overdose as they absorbed chemicals through the skin or accidentally ingested them as bubbles or bath water. Lidocaine, for example, is particularly toxic to little bodies [source: del Rey].

Why 'No Tear Shampoo' Works -- and Doesn't

If a "no tear shampoo" doesn't contain anesthetics (as urban legend suggests), then why doesn't it sting sensitive orbs? The answer lies in a few subtle changes in chemical formulas.

Adult and baby shampoos contain surfactants (short for "surface active agents"). One end of the surfactant molecule is attracted to water. The other is repelled by water but attracted to oily substances. Surfactants work by reducing the surface tension of a liquid, allowing the shampoo to spread and penetrate better, and remove the thin layer of oil known as sebum from the hair and scalp [source: Schwarcz]. Baby shampoos use detergents with long chain surfactants, such as sodium trideceth sulfate or nonionic polymers that are less harsh than normal detergents, and they use only small amounts of these cleansers in their shampoos.

Tear-free formulas also leave out surfactants such sodium lauryl sulfate, which can be irritating to the eyes and scalp. This does create a trade-off, though. Sodium lauryl sulfates -- formed in part from coconut fat or palm kernel oil -- are the chemical agents in shampoos that get hair really clean (and give a nice lather) [source: Schwarcz]. Although tear-free shampoos still clean hair, they don't remove oil as thoroughly. But since most babies don't do more than look cute and occasionally smear food into their hair, this usually works out just fine.

If you want a baby shampoo almost chemical-free, you might try making your own. It's easier than you think. All you need is castile soap -- a type of soap made exclusively from plant oils -- diluted 1-to-3 with water [source: Care2].

Keep this in mind, though: The purest shampoo out there doesn't necessarily mean you won't see any little tears at bathtime.

Your baby's bathwater -- without the use of baby soap or shampoo -- could still cause tears. It all depends on the pH level of the water, which is a measurement of the free hydrogen and hydroxyl ions in the water. A pH level measures water on a scale of 0 to 14, with 7 being neutral. If the number drops below 7, the water is increasingly more acidic, which means it has a greater amount of free hydrogen ions. Above 7, and the water is increasingly less acidic (or more basic), which means it has a greater number of free hydroxyl ions [source: USGS]. The pH range for human eyes is 6.5 to 7.6, with 7 being optimal. Any variation from neutral may cause your baby's eyes to tear, and it has little to do with the tear-free shampoo [sources: Kiechle, WHO].

Author's Note: Why doesn't tear-free shampoo sting your eyes?

I have a confession. Something happened the moment I read "Why doesn't tear-free shampoo sting your eyes?" And it was an internal dialogue that went something like this: "Because manufacturers use the same eye-burning ingredients in adult shampoos and sneak in anesthetics so babies don't feel it." Turns out, by the time I'd done oh-about-10-minutes-of-research, I knew I'd fallen victim to urban legend, too. How embarrassing.

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