“That’ll Taste Better After You’ve Had a Mouthful of Toothpaste, Kid.”

Tousle-headed Timmy is about to discover one of the worst taste combinations known to humanity: Fresh toothpaste-mouth washed down by orange juice.

Bleccchh. We’ve all accidentally combined the two. But why is it so awful?

According to mental_floss blog, it’s all chemistry, duh: One of two chemicals, sodium lauryl ether sulfate (SLES), or sodium lauryl sulfate (aka SLS), “added to toothpastes to create foam and make the paste easier to spread around your mouth.”

Both SLES and SLS mess with our taste buds in two ways. One, they suppress the receptors on our taste buds that perceive sweetness, inhibiting our ability to pick up the sweet notes of food and drink. And, as if that wasn’t enough, they break up the phospholipids on our tongue. These fatty molecules inhibit our receptors for bitterness and keep bitter tastes from overwhelming us, but when they’re broken down by the surfactants in toothpaste, bitter tastes get enhanced.

So, anything you eat or drink after you brush is going to have less sweetness and more bitterness than it normally would.

To get around this, mental_floss suggests that you use a non-foam, SLES/SLS-free paste. Make sure you tell ’em Timmy sent you.