Caries is the scientific term for tooth decay, the process by which acids produced by bacteria in your mouth dissolve the hard mineral structure of your teeth. It affects roughly 2.5 billion people worldwide, making it one of the most common chronic diseases in humans. If you’ve ever had a cavity, you’ve had caries.
How Caries Forms
Your teeth are made primarily of hydroxyapatite, a crystalline mineral composed of calcium and phosphate. Caries begins when bacteria living in the sticky film on your teeth (dental plaque) feed on sugars and starches from your diet. As these bacteria metabolize carbohydrates, they produce acids as a byproduct. Those acids lower the pH at the tooth surface, and when the pH drops below about 5.5, the hydroxyapatite crystals start to break apart, releasing calcium and phosphate ions into the surrounding saliva. This process is called demineralization.
Your mouth has a built-in recovery system. Saliva gradually neutralizes and washes away the acid, bringing the pH back up. Once the pH rises above that 5.5 threshold, minerals from saliva can redeposit onto the tooth surface, a process called remineralization. Caries isn’t a single event. It’s the result of this tug-of-war tipping toward demineralization over time. When acid attacks happen too often or last too long, the tooth loses more mineral than it gains back, and decay progresses.
Why Snacking Frequency Matters More Than Amount
The relationship between sugar and caries isn’t just about how much you eat. It’s about how often. Every time you consume something with fermentable carbohydrates, the pH in your mouth drops and stays low for a period before saliva can bring it back to neutral. This pattern, known as the Stephan curve, shows that each eating or drinking episode triggers a fresh acid attack lasting roughly 20 to 30 minutes.
If you sip a sugary drink slowly over two hours, your mouth stays acidic nearly the entire time with little opportunity for remineralization. If you drink the same amount in five minutes, the acid attack is shorter and your saliva recovers faster. Six small snacks throughout the day are far more damaging than three meals, even if the total sugar consumed is identical.
The Bacteria Behind It
Hundreds of bacterial species live in your mouth, but a few are especially important in caries. Streptococcus mutans is considered the primary driver. It thrives on sugars, produces large amounts of acid, and is particularly good at clinging to tooth surfaces and building biofilm. Once S. mutans establishes itself, it creates an acidic microenvironment that favors other acid-tolerant bacteria.
Lactobacillus species play a supporting role, particularly once decay has already started. These bacteria are especially active in the deeper layers of the tooth (dentin), where they accelerate the progression of existing cavities. The interplay between these organisms and others, including certain fungal species like Candida albicans, creates a complex community that can be difficult to disrupt once established.
Stages of Caries Progression
Caries doesn’t jump straight to a cavity. It moves through recognizable stages, and catching it early can mean the difference between a simple preventive treatment and a root canal.
- White spot lesion: The earliest visible sign. The tooth surface looks chalky or opaque in a small area. No hole has formed yet, and at this stage, the damage can often be reversed with fluoride and improved hygiene.
- Distinct enamel change: The white or brown discoloration becomes more obvious, but the surface is still intact. Remineralization is still possible, though harder.
- Localized enamel breakdown: A small breach in the enamel appears, but the deeper dentin layer underneath isn’t yet visible. This is the point where most people start to notice something is wrong.
- Shadow from dentin: The decay has reached the dentin beneath the enamel, visible as a dark shadow showing through the tooth surface. You may start experiencing sensitivity to sweets, cold, or heat.
- Visible cavity: A distinct hole with exposed dentin. Pain may come and go, especially with temperature changes or pressure.
- Extensive cavity: A large portion of the tooth structure is destroyed with widespread dentin involvement. Without treatment, the decay can reach the pulp (the nerve and blood supply inside the tooth), leading to infection, abscess, and severe pain.
How Dentists Detect Caries
Your dentist uses several tools to find decay, because not all caries is visible to the naked eye. Visual and tactile examination remains the first line of detection. Your dentist looks for color changes, chalky spots, and surface roughness, and uses an explorer instrument to feel for soft or sticky areas in the grooves of your teeth.
Bitewing X-rays reveal decay that’s hidden between teeth or beneath the surface, areas that are impossible to see directly. The X-ray shows how deep the damage extends into the dentin, which helps determine whether a filling, crown, or more extensive treatment is needed. Some offices also use laser fluorescence devices, which shine a light on the tooth and measure the fluorescence that bounces back. Healthy tooth structure and decayed tooth structure fluoresce differently, allowing the device to assign a numerical score that indicates whether caries is limited to enamel or has reached dentin.
These tools complement each other. A tooth can look fine visually but show early decay on an X-ray, which is one reason regular dental visits catch problems that brushing alone can’t prevent.
What Prevents Caries
Fluoride is the single most studied and effective tool for caries prevention. It works in two ways: it strengthens the hydroxyapatite crystal structure, making it more resistant to acid, and it promotes remineralization by helping calcium and phosphate redeposit onto weakened enamel. Community water fluoridation, introduced in the mid-20th century, reduced cavities in children by 40 to 70 percent and tooth loss in adults by 40 to 60 percent. Children born after fluoride was added to their water supply had cavity rates more than 60 percent lower than older peers who grew up without it.
Dental sealants provide a physical barrier over the deep grooves of molars where food and bacteria tend to collect. A thin resin coating is painted onto the chewing surface and hardened with a light. In studies following patients for seven or more years, people who received sealants were roughly 85 percent less likely to develop cavities on those surfaces compared to people who didn’t. Sealants are most commonly applied to children’s permanent molars shortly after they come in, but adults with deep grooves and no existing fillings can benefit too.
Daily habits form the foundation of prevention. Brushing twice a day with fluoride toothpaste, flossing to remove plaque between teeth, and limiting how frequently you consume sugary or starchy foods all reduce the number and duration of acid attacks your teeth face. Saliva is a natural protector, so anything that causes dry mouth (certain medications, mouth breathing, dehydration) increases caries risk. Chewing sugar-free gum after meals can stimulate saliva flow and speed up pH recovery.
Who’s Most at Risk
Caries can affect anyone with teeth, but some people are more vulnerable. Children and older adults have the highest rates. In children, newly erupted teeth have enamel that hasn’t fully matured and is more susceptible to acid. In older adults, gum recession exposes root surfaces, which lack the thick enamel protection of the crown and decay more easily.
People with reduced saliva flow face significantly higher risk. This includes those taking antidepressants, antihistamines, blood pressure medications, or undergoing radiation therapy to the head and neck. Frequent snacking or sipping on acidic or sugary beverages throughout the day keeps the mouth in a prolonged acidic state. Diets high in refined carbohydrates, poor access to dental care, and living in communities without fluoridated water all increase vulnerability. Orthodontic appliances like braces create additional surfaces where plaque accumulates, making thorough cleaning more difficult.