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Why Does Soap Burn My Eyes?

Why Does Soap Burn My Eyes?

We’ve all had the unfortunate experience of accidentally getting soap in our eyes. We can probably all agree that it isn’t fun, in fact, it burns! Ouch! 

What is it about soap that burns our eyes? We knew you’d ask! So we looked to our friends at Stack Exchange to get to the bottom of this irritating matter (no pun intended). 

Let’s Talk About pH

As you may have learned in science class, the pH scale measures how acidic or basic a substance is and ranges from 0 to 14. A pH of 7 is neutral, a pH less than 7 is acidic, and a pH greater than 7 is basic (alkaline).

Pure water is neutral. However, when chemicals are mixed with water, the mixture can become either acidic or basic. Examples of acidic substances are vinegar and lemon juice. Examples of alkaline substances are milk of magnesia and ammonia. 

The Human Eye

Human eyes have a natural pH level of around 7, which is neutral. Our eyes are extremely sensitive to any variations in pH and have a very low tolerance for alkalinity. Soaps have a pH of between 7.5 and 9, so their chemical nature is more alkaline. 

Since our eyes can't handle an alkaline substance, they begin watering to get rid of the potentially harmful substance. Blood vessels then enlarge, coming closer to the surface of the eye and making them appear red. This is what we usually experience when soap gets in our eyes. 

Thankfully, before soaps are put on the market, they are tested to ensure they are non-toxic if they do come into contact with eyes. Even so, it’s best to try to keep soap out of your eyes as much as possible. After all, no one wants to have stinging, red eyes!

Looking for more Never Stop Asking "Why?" questions? Catch up on all of the past "Why's" on the blog!