Toothpaste is roughly half abrasive particles by weight, with water making up another 20 to 40 percent. The rest is a mix of humectants, fluoride, surfactants, thickeners, flavoring, and sweeteners, each serving a specific purpose beyond just freshening your breath. Here’s what each of those ingredients actually does.
Abrasives: The Cleaning Power
About 50% of your toothpaste is made up of fine abrasive particles. These are the ingredients that physically scrub stains and plaque off your teeth when you brush. The most common abrasive is hydrated silica, a form of silicon dioxide. You’ll also find calcium carbonate (chalk, essentially) and calcium phosphate compounds in many formulas.
Not all abrasives are created equal. Toothpastes are rated on a scale called Relative Dentin Abrasivity, or RDA, which measures how aggressively a paste wears on the softer layer beneath your enamel. The scale breaks down like this:
- Below 20: very low abrasion
- 20 to 40: low abrasion
- 40 to 60: moderate abrasion
- 60 to 80: strong abrasion
- Above 80: very strong abrasion
Everyday cavity-protection toothpastes typically fall in the low to moderate range. Whitening toothpastes tend to score much higher. In lab testing, some whitening formulas scored above 140, while sensitivity toothpastes scored in the mid-20s. If you have exposed roots or worn enamel, a lower RDA paste will be gentler on your teeth.
Fluoride: The Cavity Fighter
Fluoride is the ingredient most responsible for toothpaste’s ability to prevent cavities. It works by strengthening enamel and helping to reverse the earliest stages of tooth decay before a cavity fully forms. The WHO recommends a concentration between 1,000 and 1,500 parts per million (ppm) of fluoride for all age groups as the standard for cavity prevention.
Three fluoride compounds appear most often in toothpaste sold in the United States: sodium fluoride, sodium monofluorophosphate, and stannous fluoride. They all deliver fluoride ions to your teeth, but stannous fluoride also has antibacterial properties, which is why it shows up in formulas targeting gum health. The European Union recognizes over 20 different fluoride compounds for use in oral care products, though most consumers will only encounter those three.
A common misconception is that children need a special low-fluoride toothpaste. The WHO notes there’s a lack of evidence that toothpastes below 1,000 ppm fluoride actually prevent cavities. The recommendation is to use regular-strength toothpaste for all ages and simply control the amount: a rice-grain smear for children under 3, a pea-sized amount for ages 3 to 6, and a pea-sized amount without rinsing afterward for everyone older.
Water and Humectants
Water accounts for 20 to 40% of toothpaste and acts as the solvent that holds everything together. But water alone would cause the paste to dry out and harden in the tube. That’s where humectants come in.
Most toothpastes contain sorbitol, glycerin, or both. These compounds trap moisture and keep the paste smooth and squeezable from the first use to the last. They also pull double duty as mild sweeteners, each about half as sweet as table sugar, which makes the paste more pleasant without feeding the bacteria that cause cavities. Sorbitol and glycerin are sugar alcohols, so they don’t promote tooth decay the way actual sugar would.
Surfactants: Why Toothpaste Foams
The foaming action you feel while brushing comes from a surfactant, most commonly sodium lauryl sulfate (SLS). Used in toothpaste for over 50 years, SLS typically makes up 0.5 to 2% of the formula. It lowers the surface tension of the paste, helping it spread across your teeth and lift debris away. The foam also creates that familiar feeling of cleanliness.
SLS can irritate soft tissue in some people, particularly those prone to canker sores or sensitive gums. Some manufacturers have switched to milder alternatives like stearyl ethoxylate, a non-ionic surfactant that produces less foam but is gentler on the mouth. In clinical trials comparing the two, users rated the SLS version significantly higher for foaming and freshness, but both performed similarly for actual cleaning. Some fluoride formulas skip added surfactants entirely because the fluoride compound itself has surfactant properties.
Thickeners and Binders
Without thickeners, toothpaste would be a watery slurry. Ingredients like xanthan gum and cellulose gum give the paste its body, keeping the abrasive particles evenly suspended so they don’t settle to the bottom of the tube. Xanthan gum is particularly well suited for this job because it creates high viscosity at very low concentrations. A solution of just 1% xanthan gum appears almost gel-like at rest but flows easily under pressure, which is exactly what you want when you squeeze a tube. It’s also resistant to acids, alkalis, and enzymes, giving it stable shelf life for months at room temperature.
Specialty Ingredients for Sensitivity
If you’ve used a toothpaste marketed for sensitive teeth, it likely contains 5% potassium nitrate as its active desensitizing ingredient. Tooth sensitivity happens when the softer inner layer of a tooth, called dentin, becomes exposed. Tiny channels in the dentin transmit sensations from hot, cold, or sweet foods directly to the nerve.
Potassium nitrate works by flooding those channels with potassium ions, which build up around the nerve fibers. At high enough concentrations, the potassium prevents the nerve from firing and resetting normally, essentially calming it down. The effect is gradual. Most people need to use the toothpaste consistently for a few weeks before noticing a significant reduction in sensitivity.
Whitening Toothpaste Ingredients
Whitening toothpastes use two strategies. The first is simply more aggressive abrasives, which physically scrub surface stains from coffee, tea, or red wine. These formulas tend to have higher RDA scores.
The second approach is chemical whitening with hydrogen peroxide. Whitening toothpastes contain peroxide at concentrations of 3 to 5%, which is significantly lower than professional or at-home bleaching products (which use the equivalent of 10% carbamide peroxide applied for hours at a time). Lab studies show that even a 5% hydrogen peroxide toothpaste, used for 90 seconds at a time, produces less color change than dedicated bleaching trays. The tradeoff is that whitening toothpastes are more convenient and less likely to cause sensitivity, but they work slowly and have a lower ceiling for results.
Flavoring, Sweeteners, and Color
The minty taste most people associate with toothpaste comes from flavoring oils like spearmint, peppermint, or wintergreen. These don’t clean your teeth, but they make brushing more tolerable and leave your mouth feeling fresh. Artificial sweeteners like saccharin are sometimes added alongside the sweetness from sorbitol and glycerin. Colorants, typically titanium dioxide for white pastes or food-grade dyes for gels, round out the formula. None of these ingredients affect dental health, but they play a real role in whether people actually use the product consistently.
Natural and Fluoride-Free Formulas
A growing number of toothpastes replace fluoride with hydroxyapatite, a synthetic form of the mineral that makes up most of your tooth enamel. The idea is that applying hydroxyapatite directly to the tooth surface can fill in microscopic defects and strengthen enamel without fluoride. These products are popular in Japan and gaining traction elsewhere, though fluoride remains the ingredient with the deepest body of evidence behind it.
Natural toothpastes also commonly feature xylitol, a sugar alcohol that bacteria can’t metabolize into the acids that cause cavities, and activated charcoal, marketed as a stain remover. Charcoal acts as a physical abrasive but can be quite harsh on enamel, and its actual whitening benefit beyond what any abrasive would provide is limited. If you choose a fluoride-free option, checking that it contains at least some evidence-backed active ingredient, like hydroxyapatite or xylitol, gives you a better chance of real cavity protection.