Fluoride: What It Actually Does (And Why Everyone's So Loud About It)

Fluoride gets more shouting than almost anything else in dentistry. Half the internet says it's poison. The other half says skip it and you're basically asking for dentures by 40. Neither is true, and the actual story is much less dramatic than either side wants it to be.

Here's what fluoride is really doing. Your enamel is mostly a mineral called hydroxyapatite. Every day, acid from the bacteria in plaque nibbles away at it — that's demineralisation. Your saliva pushes minerals back in — that's remineralisation. It's a tug of war that happens constantly, whether you notice it or not. Fluoride doesn't stop the acid attacks. It changes what gets rebuilt. Enamel that remineralises with fluoride present forms fluorapatite instead of plain hydroxyapatite, and fluorapatite is genuinely more acid-resistant. Same tooth, tougher finish.

That's it. That's the mechanism. No mystery, no conspiracy.

Where the argument comes from

Most of the fear traces back to two things: dosage confusion and old research on very high-fluoride water areas, mostly abroad, with levels nowhere near what's in UK water or toothpaste. At the concentrations actually used here — around 1,450 ppm in adult toothpaste — the evidence for benefit is strong and the evidence for harm just isn't there. The one real, well-documented risk is fluorosis, and that's a cosmetic issue in developing teeth from swallowing too much toothpaste as a young child, not a systemic health risk. It's also entirely avoidable.

What I actually tell patients

• Adults: pea-sized amount, 1,450 ppm, twice a day, don't rinse afterwards. Rinsing washes away the whole point of putting it there.

• Children under 3: smear, not a pea. Supervise brushing so they're not swallowing it.

• Children 3–6: pea-sized, supervised, same rule about not rinsing.

• If your water supply is already fluoridated, you don't need extra fluoride supplements or fluoride mouthwash on top — more isn't better here, it just raises fluorosis risk in kids for no added benefit.

And the fluoride-free crowd?

Some of you will still choose fluoride-free toothpaste, for your own reasons, and that's your call to make. If you do, the trade-off is real: you're relying entirely on brushing mechanics and diet to protect your enamel, with none of the chemical backup. Hydroxyapatite toothpastes are a legitimate alternative with their own evidence base, not snake oil — but for most people, most of the time, standard fluoride toothpaste at the right concentration, used correctly, is still the simplest way to keep your teeth ahead in that daily tug of war.

Just bloody brush. Fluoride just makes the brushing count for more.

Related reading: Sugar: It's Not the Amount. It's the Frequency. | Why Your Gums Bleed When You Brush. And What It Actually Means.