"Sugar rots your teeth!" You've likely heard those words, in some shape or form, from a parent, grandparent, teacher, or TV show. In school, you might have even put an egg into a cup of soda to watch the shell turn soft and flabby after a few days. That, the lesson implies, is what sugary soda does to your teeth.
However, sugar alone is not the whole story behind cavities. Nor is it a corrosive substance, as the classroom experiment implies: in fact, it's the tangy acid in the soda that softens the shell, not the sugar.
Sugar, however, is a great energy source for the bacteria living in your mouth that can cause tooth decay, says Dr. Diana Nguyen, a dentist at a university dental school. But should we really blame sugar alone for cavities? The answer is more nuanced than you might think.
What actually causes cavities?
Our mouths are hosts to hundreds of types of bacteria. The main culprits behind cavities, though, are Streptococcus mutans and various types of Lactobacillus bacteria. These bacteria get a boost from carbohydrates, which they consume for energy.
When you eat something starchy or sugary (yes, sugar is a carbohydrate), these bacteria leap into action, breaking down carbs and producing lactic acid in the process. It's that acid which weakens dental enamel (the hard white coating on teeth that protects them), eventually causing cavities.
But the human body does have a way of fighting back. "It's not like you eat sugar, and then your mouth is acidic forever," Nguyen says. Saliva plays an important role in bringing the pH level in your mouth back up to neutral. When you eat a chocolate bar or a piece of bread (or just about anything), your mouth waters, which helps to flush away harmful acids. Usually, your saliva can accomplish this task in around 30 minutes.
How do you prevent cavities?
So while sugar doesn't eat away at teeth directly, it feeds the bacteria that do the damage, and it can accelerate cavities, as can acid from soda or other acidic drinks.
Timing also matters. Constantly consuming carbohydrates or acidic drinks can make it hard for your saliva to return to a neutral pH level.
"People who are at higher risk of cavities are very often those who snack or drink sugary drinks or acidic drinks throughout the day," says Nguyen. "If you're constantly exposing your mouth to carbohydrates and acids, then you're going to keep that pH level in your mouth down, and that will allow acid to continue to demineralize the enamel."
Nguyen points out that, historically, people still got cavities even when refined sugar wasn't as widely available. When people eat or drink carbohydrate- or acid-rich things at frequent intervals throughout the day, the mouth never has enough time to return to a normal pH.
When should you brush your teeth after having sugar?
Nguyen recommends waiting 20 to 30 minutes after eating before brushing your teeth. "We would not recommend brushing the teeth right away after having an acidic drink or right after having a snack," Nguyen says. You want to first give your mouth time to get things back to normal.
Brushing when your mouth is more acidic can do more harm than good. "When that pH level is lowered, when your mouth is more acidic and those bacteria are active, [that acid] actually softens the enamel," says Nguyen. If you then brush your teeth while that acid is hanging out, it can damage your enamel.
"Some people are trying to stay on top of their oral health. They want to keep their teeth healthy. They just had sugar, or they just had something acidic, and they think, 'Okay, I've got to get this off my teeth right away.' But they could actually inadvertently cause more damage to their tooth structure," Nguyen says.
If you can't wait 30 minutes after eating to brush, water is your best friend. "Chase whatever you're eating or drinking with a sip of water to dilute that acidity," Nguyen says. "That can help reduce the chance of inadvertent damage to your teeth."
Along with sips of water, regular brushing and flossing can also help mitigate the effects of acid-producing bacteria in your mouth. Sticky plaque is actually bacterial buildup on teeth, and the acid those bacteria produce can harm your teeth unless the plaque is regularly removed.
Sugar still fuels the bacteria that cause cavities, and constantly eating or drinking it can keep your saliva from returning your mouth to a neutral pH. Keeping an eye on what and when you're eating and drinking can help keep your mouth healthy.