Why doesn't shampoo made for babies cause their eyes to sting?

It’s bath time for your little one, and everything is just right. The water temperature is warm but not too hot, the cozy towel is ready, and the gentle baby shampoo is within arm's reach.

Even though baby’s hair doesn’t require much care yet, the few strands on top still need a little attention. Soon, you're lathering up those soft locks with lavender-scented baby shampoo, making bubbles in no time.

Just as you’re about to give yourself a pat on the back for successfully cleaning your little one, panic strikes. A cascade of bubbles is on the move, escaping from her head and heading toward her eyebrows—and, oh no!—her eyes. Before you can react, she blinks, sending the suds on a journey across her eyes. And she smiles.

She smiles? Where's the typical painful sting that comes with shampoo getting into the eyes? Then it dawns on you: This is baby shampoo. Tear-free. No tears. A formula designed without the usual discomfort.

While you're relieved, a thought crosses your mind: Why doesn’t this shampoo irritate her eyes? An adult version would certainly sting (you’ve learned that the hard way), so why does the baby shampoo act differently?

Chances are, if you were to ask this at your baby’s next playdate, someone might let you in on the ‘no tears’ secret: The formula contains the same eye-irritating chemicals found in adult shampoos, but with a numbing agent—Novocain, lidocaine—to dull the pain.

Which, on the surface, makes sense—except it's not true. Baby shampoos don't contain anesthetics. If they did, your hands would go numb from washing baby’s hair, and children could accidentally ingest harmful chemicals, risking overdose. Lidocaine, for example, is especially dangerous for little bodies [source: del Rey].

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

If a ‘no tear shampoo’ doesn’t contain numbing agents (as some myths claim), then why doesn’t it cause any discomfort to those sensitive little eyes? The secret lies in some clever tweaks in the chemical formulation.

Both adult and baby shampoos are made with surfactants (short for ‘surface active agents’). One end of a surfactant molecule is drawn to water, while the other end repels water but clings to oily substances. These surfactants lower the surface tension of liquids, allowing the shampoo to spread more evenly and remove the oily coating known as sebum from the hair and scalp [source: Schwarcz]. Baby shampoos use milder detergents with longer chain surfactants like sodium trideceth sulfate or nonionic polymers, and they use smaller quantities of these cleansing agents, making them gentler than typical adult shampoos.

Tear-free formulas also avoid harsh surfactants like sodium lauryl sulfate, which can be irritating to the eyes and scalp. But there's a catch: Sodium lauryl sulfate—derived from coconut fat or palm kernel oil—are the key ingredients that make shampoos lather up and clean hair thoroughly [source: Schwarcz]. While tear-free shampoos still clean hair, they don’t strip away oils as completely. But since babies aren’t typically engaging in messy outdoor adventures, this usually doesn’t pose a problem.

If you want a nearly chemical-free baby shampoo, consider making your own. It’s simpler than you think. Just use castile soap—made entirely from plant oils—and dilute it 1-to-3 with water [source: Care2].

However, keep in mind: The purest shampoo doesn’t necessarily guarantee a tear-free bath time.

Even without baby soap or shampoo, your baby’s bathwater might still lead to tears. This depends on the water’s pH level, which measures the concentration of free hydrogen and hydroxyl ions. The pH scale ranges from 0 to 14, with 7 being neutral. Water below 7 is increasingly acidic, meaning more free hydrogen ions, while water above 7 is more basic, with more free hydroxyl ions [source: USGS]. The ideal pH for human eyes is between 6.5 and 7.6, with 7 being the best. If the water strays from neutral, it can cause discomfort and tears in your baby’s eyes, and this has little to do with the shampoo [sources: Kiechle, WHO].