What actually stains your teeth — and one piece of advice that does not hold up

Stain does not attach to your enamel. It attaches to the film on top of it.

Within minutes of any cleaning, proteins from saliva form the acquired enamel pellicle across the tooth surface. Pigmented compounds from what you eat and drink — tannins from tea, tannins and anthocyanins from red wine, melanoidins from coffee, tar from tobacco — adsorb onto that protein layer. Certain cationic agents, chlorhexidine among them, then precipitate those chromogens into a darker, more tenacious deposit.

This is why staining returns on a schedule rather than accumulating steadily forever, and why it returns quickly after a cleaning: the film reforms within hours, and the process begins again.

Tea is worse than coffee

Counterintuitive, given coffee is darker in the cup. A 2022 study comparing eleven beverages on human enamel found black tea and red wine produced the greatest colour change, with black tea also the most resistant to removal by brushing. Coffee stained significantly compared with water, but less than either.

One honest caveat: that study used a chlorhexidine-cycling model, and chlorhexidine specifically amplifies tannin precipitation. Tea is tannin-heavy, so the margin over coffee may be exaggerated relative to someone not using a chlorhexidine rinse. The ranking is real and repeated. The size of the gap is less certain than a single study makes it look.

Tobacco, at population scale

A cross-sectional study of 3,215 UK adults found 28% of smokers reported moderate or severe tooth discolouration, against 15% of non-smokers — odds ratios of 1.7 for moderate and 2.4 for severe discolouration. This is one of the few staining findings measured in a real population rather than on extracted teeth in a lab.

The advice that does not hold up

You have been told to wait thirty to sixty minutes before brushing after something acidic, on the theory that brushing softened enamel scrubs it away.

A 2020 systematic review and meta-analysis pooled eleven studies on exactly this question. In human enamel, delayed brushing did not significantly reduce erosive wear. The protective effect that made this advice famous appeared in bovine enamel, which behaved significantly differently. There were no human dentine studies at all.

The same review did find something that worked: fluoride toothpaste offered meaningful protection. So the actionable version of this advice is closer to "use a fluoride toothpaste" than "wait an hour."

We are not telling you to ignore it. The ADA still recommends rinsing with water rather than brushing immediately after acidic drinks, and rinsing costs nothing. But there is a genuine, live gap between that guidance and the best current synthesis of the evidence, and you should know which of the two you are following.

Straws, honestly

The straw advice traces back to work measuring how drinking method affects tooth-surface pH. It found that how long a drink stays in your mouth matters a great deal — holding or slowly sipping produced the most pronounced pH drop, gulping the least.

That is a measurement of pH, not of staining and not of clinical wear. The ADA does recommend positioning a straw behind the front teeth. It is a reasonable extrapolation from a surrogate measure, and we would rather call it that than present it as a tested outcome.

What we could not support

The common claim that acidity increases how much stain your teeth pick up afterwards. It is mechanistically plausible — acid roughens and demineralises enamel, and rougher surfaces hold more pigment. We could not find good direct evidence demonstrating it in humans, so we are not going to assert it.

What actually follows from all this

Tea and red wine deserve more respect than coffee gets blamed for. Tobacco is in a category of its own. Rinsing with water is free and probably worth doing. Fluoride toothpaste has better evidence behind it than the waiting rule it is usually mentioned alongside. And because the pellicle reforms within hours of every cleaning, no amount of care makes staining a problem you solve once.