There’s one part of my morning that stays consistent. I have breakfast before I brush my teeth. Why? Because I want to actually enjoy my food. I remember the first time I made the mistake of having orange juice after brushing my teeth. Here I was, expecting a refreshing burst of vitamin C—raw energy in a glass—and instead I got hit with the worst taste my mouth has ever known.

Why does toothpaste and mouthwash make orange juice taste so bad?

The Mystery of Taste

Similar to our sense of smell, scientists aren’t entirely sure how taste works. Scientists have, however, come to a general consensus as to what creates this awful taste combination of orange juice and toothpaste.

They believe that flavors are a result of microscopic interactions between taste molecules and receptors on your tongue. Molecules of a certain shape will interact with receptors that are shaped to accept them. But these receptors can be manipulated, which is probably the best explanation for why orange juice and toothpaste taste gross together.

The Likely Culprit

Sodium lauryl sulfate (SLS) is a surfactant added to toothpaste. A surfactant is a substance that reduces the surface tension of a liquid in which it is dissolved. It creates the bubbly froth that toothpaste becomes after you begin brushing, and does so by lowering the surface tension of the saliva in your mouth. The froth creates an illusion to a clean mouth after brushing.

Sodium lauryl sulfate suppresses your sweet receptors. This could explain its affect on orange juice’s sweetness. In addition, SLS eliminates phospholipids, which are fatty compounds act that act as inhibitors (stoppers) on your bitter receptors. It’s in this way that SLS dulls the sweetness and promotes the bitter taste in orange juice.This is not the only explanation of why orange juice and toothpaste

This is not the only explanation of why orange juice and toothpaste combine to make a bad flavor, but it’s the most widely accepted one. So the next time you accidently drink a mouthful of juice too soon after brushing, blame it on the foam.

Conclusion

Peanut butter and jelly—good. Chocolate and vanilla—also good. Ketchup and fries—the best. Toothpaste and orange juice—don’t go there.