Have you ever had that first swig of orange juice in the morning and found that it tasted just … horrible?   If so, good for you! You must have some pretty good oral hygiene!   Brushing your teeth right before you eat is usually a recipe for a nasty meal.   Toothpaste makes practically any food go from delicious to cringe-worthy, but the effect is particularly bad with orange juice.     Why?   Well despite what many folks think, it’s not the mint in your toothpaste that makes your food taste gross.    It’s a compound called sodium lauryl sulfate, and other chemicals with similar-sounding names.    All of these compounds are surfactants. Their job is to lower the surface tension between different kinds of liquids -- or between a liquid, like water, and solids, like fats.    Their ability to do this makes surfactants really effective detergents and foaming agents, so they show up in everything from dish soap to shampoo, and, of course, in your toothpaste.   But surfactants can also seriously mess with your taste buds.   So your taste buds can detect five different kinds of tastes. They have receptors for sweet, bitter, and umami, plus ion channels that detect levels of salt, as well as acidity, which your brain interprets as sour.   Surfactants do two terrible things to those receptors: First, they make it harder to taste sweetness, and then, they make it easier to taste bitterness.   So, after you’ve brushed your teeth, and you still got a little bit of residue from the toothpaste in your mouth, that sodium lauryl sulfate just slots itself right into your sweet receptors.    When you take a swig of OJ, it keeps those receptors from receiving the signal that, “hey, there’s sugar in this!”   And at the same time, that compound messes with some molecules that are usually hanging around on your tongue, called phospholipids, which block your bitterness receptors.    Phospholipids are a type of fat, and surfactants are designed to break down fats and oils -- so that’s exactly what your toothpaste does to them.    With your sweet receptors blocked and your bitter ones wide open, food that’s normally delicious suddenly turn out to be kind of terrible, because you can taste none of the sweet, and all of the bitter.   People tend to notice this effect most often with orange juice, because it’s quite sour beneath all that sugar, and it’s also just something that people tend to drink in the morning, right after they’ve brushed their teeth.   Now if you want to avoid that bitter taste, you can use toothpaste that doesn’t have any sodium laur-anything in its ingredients, or you can just drink your orange juice a little later in the day.   Thanks for asking! If you have any other questions for us we’re on Facebook, and tumblr, and twitter, and in the comments down below, and don’t forget to go to youtube.com/scishow and subscribe!