Tooth decay is the single most common chronic disease in the world. Globally, about 3.69 billion people live with at least one major oral condition, and untreated cavities in permanent teeth top the list, affecting roughly 27.5% of the global population. In the United States, the numbers are just as striking: 96% of adults aged 65 and older have experienced decay at some point in their lives.
Global and U.S. Numbers
A 2024 analysis published in The Lancet, drawing on data from 1990 to 2021, found that untreated cavities in permanent teeth had an age-standardized prevalence of about 27,500 per 100,000 people worldwide. That makes cavities more common than any other oral condition, including gum disease and tooth loss combined. The global economic toll reflects this: oral diseases cost an estimated $710 billion in 2019, split between $387 billion in direct treatment costs and $323 billion in lost productivity.
In the U.S., roughly one in four adults between ages 20 and 64 has at least one untreated cavity right now. CDC data from 2015 to 2018 puts the rate at 25.9% for adults aged 20 to 44 and 25.3% for those aged 45 to 64. Those numbers capture only untreated decay, meaning they don’t count the fillings, crowns, and root canals already in people’s mouths. When you include both past and current decay, the percentage climbs dramatically, especially among older adults.
Decay Rates by Age
Cavities can start as soon as a child’s first teeth come in. Data from the National Institute of Dental and Craniofacial Research shows that 23% of children aged 2 to 5 have already had cavities in their baby teeth, and 10% of that age group have decay that hasn’t been treated yet. Among those affected, children in this age range had an average of three filled teeth and two decayed ones.
The picture gets worse with age. By the time Americans reach 65, nearly everyone has been affected. About 96% of seniors have had decay at some point, and approximately 17% have lost all their teeth entirely. Older adults face a compounding problem: receding gums expose the softer root surfaces of teeth, which are more vulnerable to acid than enamel. Decades of wear, dry mouth from medications, and reduced access to dental care all pile on.
Income Is a Major Factor
Tooth decay doesn’t hit every group equally. Low-income adults (those living below 200% of the federal poverty level) have two to three times more untreated cavities than higher-income adults. Among people with one to three untreated cavities, the rate for low-income adults is nearly double: 26.2% compared to 13.2%. The gap widens further for people with four or more untreated cavities, where the low-income rate of 13.2% is more than triple the 3.9% seen in higher-income adults.
This disparity reflects access more than behavior. Dental insurance coverage, proximity to providers, and the cost of treatment all play roles. People without insurance are far less likely to get early cavities filled, which means small problems become bigger, more expensive ones over time.
How Cavities Actually Form
Your mouth is home to hundreds of species of bacteria. Some of them feed on sugars and starches from the food you eat, producing acids (primarily lactic acid) as a byproduct. These bacteria cluster together in a sticky film called plaque that clings to tooth surfaces, concentrating acid right against the enamel.
Enamel starts dissolving when the pH at the tooth surface drops below about 5.5. For context, your saliva normally sits around pH 6.7 to 7.4, which is neutral enough to keep enamel intact. Every time you eat something sugary or starchy, bacteria in plaque pull that local pH down. If it stays below 5.5 long enough and often enough, minerals leach out of the enamel faster than saliva can replace them. That’s the beginning of a cavity. At a pH of 4.0, research shows complete mineral loss can occur in the affected area within weeks.
This is why frequency matters as much as quantity. Sipping a sugary drink over several hours keeps the pH low for an extended period, doing more damage than drinking the same amount all at once. Saliva is your main natural defense: it neutralizes acids, washes away food particles, and delivers calcium and phosphate back to weakened enamel. Anything that reduces saliva flow (certain medications, mouth breathing, dehydration) raises your risk.
What Reduces Cavity Rates
Fluoride remains the most effective population-level tool against tooth decay. Community water fluoridation reduces cavities by about 25% in both children and adults. Fluoride works by integrating into the enamel crystal structure, making it more resistant to acid, and by promoting remineralization of early-stage damage before a cavity fully forms. Fluoride toothpaste provides a similar benefit at the individual level.
Beyond fluoride, the basics matter more than any single product. Brushing twice a day disrupts plaque before it hardens into tarite. Flossing or using interdental brushes clears bacteria from the tight spaces between teeth where most cavities in adults actually start. Limiting how often you snack on sugary or starchy foods gives saliva time to do its repair work between meals.
The World Health Organization’s Global Oral Health Action Plan has set a target of reducing the combined global prevalence of major oral diseases by 10% by 2030, alongside getting 80% of the world’s population access to essential oral health care. Given that cavity rates have remained stubbornly high for decades despite being almost entirely preventable, meeting those targets would require significant expansion of dental care access in low- and middle-income countries, where most untreated decay is concentrated.