Most people have probably made the mistake of drinking orange juice immediately after brushing their teeth. The effect generated isn’t a pleasant one—the resulting taste is bitter, with none of the original sweetness of orange juice. Research suggests that this effect can last up to 30 minutes after the use of toothpaste, and it can also be subtly noticed with other foods.

The root of the effect

The root of the effect can be found in one of the chemical constituents of toothpaste. Sodium lauryl sulfate is a compound commonly used in personal care products, including toothpaste, shampoo and shower gel. It acts as what chemists call a “surfactant.” Essentially, the molecule has one end which will dissolve in water and one end which is insoluble in water, but soluble in grease and oils. This helps it dissolve and remove dirt when you wash your hair. It also stimulates foaming; in toothpaste, it lowers the surface tension of saliva, allowing a foam to form. Sodium laureth sulfate is a chemical commonly used instead of sodium lauryl sulfate, but it performs exactly the same role. Some rumors have falsely claimed that these chemicals are cancer causing, but there is scientific evidence that they are completely safe at the concentrations we usually encounter.

Sodium lauryl sulfate in toothpaste

The presence of sodium lauryl sulfate (or its alternative) in toothpaste is thought to be the cause of its effect on the taste of orange juice. The commonly accepted explanation for this effect is that sodium lauryl sulfate suppresses the receptors in your mouth that help you detect sweetness. At the same time, it’s also thought they can alter membranes formed by compounds called phospholipids, which usually inhibit your bitter taste receptors to an extent. As a consequence, when you drink orange juice immediately after toothpaste, the sweet taste is dulled and the bitter taste is emphasized, producing the somewhat unpleasant effect.

Alternatives to sodium lauryl sulfate

If, for whatever reason, you want to avoid this unfortunate effect of toothpaste (instead of never brushing your teeth again), there are alternatives to sodium lauryl sulfate toothpastes. These often use glycyrrhizin, a compound isolated from licorice root, in order to produce their foaming effect.