Understanding Tooth Decay: How Cavities Form and How to Stop Them

Dental caries — better known as tooth decay or cavities — is the most common chronic disease in the world. According to the World Health Organization, untreated decay in permanent teeth affects an estimated 2.5 billion people. The good news is that it is largely preventable.

Decay is caused by bacteria in dental plaque, mainly a species called Streptococcus mutans. These bacteria break down the free sugars in food and drink and turn them into acids. Over time, repeated acid attacks strip minerals from the enamel. At first this shows up as a chalky white spot; if it continues, the enamel breaks down and a cavity forms.

Whether decay advances, stops, or even reverses depends on a balance between damaging factors (frequent sugar, plaque, low fluoride) and protective factors (saliva, fluoride, good cleaning). Early decay confined to the enamel can sometimes be reversed with fluoride and better home care — which is exactly why catching it early at a check-up matters so much.

To prevent cavities: brush twice daily with fluoride toothpaste, clean between your teeth every day, and limit how often you have sugary foods and drinks. It is the frequency of sugar, not just the total amount, that drives decay — constant snacking keeps your mouth acidic for longer. Chewing sugar-free gum containing xylitol can help by boosting saliva flow.

Symptoms such as tenderness or pain usually appear only in the later stages, so don't wait for discomfort. Regular dental visits allow decay to be spotted and treated while it is still small.

Sources: World Health Organization; StatPearls / U.S. National Center for Biotechnology Information; Merck Manual; American Dental Association.