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Toothpaste aisles are designed to make this feel complicated. It is not. The single most useful thing on the packet is a number, and it is almost never on the front.
Fluoride, and the number to look for
Fluoride works in the mouth, not in the body. It makes the enamel surface more resistant to acid and helps it take minerals back after an acid attack. That is the mechanism, and it is why leaving it on the teeth matters as much as putting it there.
For adults and children aged seven and over, the figure to look for is 1,350–1,500 ppm. It is usually in the ingredients panel. Anything substantially below that is doing less, whatever the box says.
Higher-strength prescription pastes exist — 2,800 and 5,000 ppm — for people with a lot of decay, dry mouth, or exposed root surfaces. 2,800 ppm is used from age 10 and 5,000 ppm from 16. Those come from a dentist, with instructions.
For children, the amount matters as much as the concentration, and both change with age. That has its own guide.
The rinse, which almost everyone gets wrong
Brush, spit out the excess, and stop.
Rinsing with water, or with mouthwash, immediately after brushing removes the film of fluoride you just applied. Leaving it there is free, takes no effort, and is one of the highest-value habits in this entire library.
If the taste bothers you, rinsing an hour later is fine.
Whitening toothpastes
These remove surface stain. They do not change the underlying colour of your teeth, because the colour of a tooth comes from the dentine beneath the enamel and no paste reaches it.
They are not usually harmful, but some are more abrasive. If you have sensitivity, exposed root surfaces or significant tooth wear, an abrasive paste is the wrong choice.
Sensitive toothpastes
These are the first genuine exception, and they do work — but slowly. Most use potassium nitrate to calm the nerve, or stannous fluoride to block the tubules in exposed dentine. Give one two to four weeks of consistent use before judging it, and keep using it afterwards; the effect fades if you stop.
SLS and ulcers
The second exception. Sodium lauryl sulfate is the detergent that makes toothpaste foam. A minority of people who get recurrent mouth ulcers find they get noticeably fewer on an SLS-free paste. If that is you, it is worth a month’s trial.
What does not matter much
- Gel or paste
- Flavour, beyond whether you will actually use it
- Striped, charcoal, "natural", or whitening claims on the front
If a toothpaste contains 1,350 ppm fluoride or more and you will actually use it twice a day, it is a good toothpaste. Everything else on the tube is a smaller decision than that one.
