It's happened to everyone. You brush your teeth and take a swig of orange juice. It tastes bitter and disgusting. But why does toothpaste make orange juice and other foods taste like a bitter pile of trash?
The answer is pretty simple. Toothpaste contains a detergent called sodium lauryl sulfate or SLS. It's in the vast majority of toothpaste. It helps to create that foamy feeling and, importantly to this conversation, it helps to break down fats.
SLS does strange things to your taste buds while it works its magic. Taste buds have receptors for sweet, bitter, and umami, which is a receptor for savory tastes. There are also two ion channels that detect when things are salty or acidic, which is interpreted by your brain as sourness. SLS does two things here. It blocks the taste buds that detect sweetness and breaks down phospholipids, a type of fat, on your tongue. Those phospholipids inhibit how much bitterness you are able to taste.
Thus the SLS is simultaneously blocking the sugary flavors of orange juice and allowing your tongue to fully taste the bitterness present.
The SLS in toothpaste actually alters the taste of many foods. However, the combination of orange juice being regularly consumed in the morning and how sour it is underneath the sugar make it a touchstone for how this process works.
Unfortunately, knowing how this process works won't stop it from happening. In fact, a 2005 study attempted to quantify how long it takes until tastes return to normal. Subjects in the study consumed orange juice, coffee, sausage, and processed cheese after brushing with "a strongly mentholated toothpaste." Fatty, solid foods had their taste return quickly, but it required at least an hour for orange juice to not taste like an edible dumpster fire.
So, if you have to brush before you consume orange juice and have no desire to cringe, plan accordingly.
Sign up here for our daily Thrillist email, and get your fix of the best in food/drink/fun.