On the crimped end of a toothpaste tube there is a small coloured rectangle, and a very large number of people believe it is a code.
Green means all natural. Blue means natural plus medicine. Red means natural plus chemicals. Black means pure chemicals. The version varies, the confidence does not, and it has been circulating in one form or another for decades.
It is not true. Not approximately true, not true for some brands, not a deprecated system that used to mean something. The mark has a function, that function is entirely mechanical, and understanding what it actually does is more interesting than the myth.
What the Mark Is Actually For
A toothpaste tube is not made as a tube with a design printed on it afterwards. The printing is done on a continuous web or on preformed sleeves, and the tube is then filled and the end is crimped and sealed by a machine running at high speed.
That machine has to know exactly where it is on the printed material. If it cuts or seals in the wrong place, the design ends up misaligned – the logo half on the crimp, the text running off the edge – and the product is unsellable.
So the printing includes a registration mark: a small block of solid colour in a position the machine can detect with an optical sensor. The sensor finds the mark, the machine knows precisely where the printing sits, and the cut and the seal happen in the right place relative to the design.
That is the whole explanation. It is a target for a photocell.
The colour is chosen for one reason: it has to contrast strongly with whatever is immediately around it so the sensor can see it reliably. On a tube with a pale design the mark will be dark. On a dark design it will be light. The choice is made by whoever prepared the artwork, on the basis of what the sensor needs, and there is no registry, no standard and no meaning.
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Why This Particular Myth Will Not Die
Plenty of false claims circulate and most of them fade. This one has survived for decades across multiple waves of media, and the reasons it survives are worth separating out, because they apply to a whole category of things people believe.
It explains something otherwise unexplained. The mark is genuinely there, it is genuinely unexplained on the packaging, and people notice it. An unexplained thing is an open question, and an open question will accept almost any answer that arrives first.
It flatters the person repeating it. The claim is framed as hidden knowledge that manufacturers would prefer you did not have, which makes passing it on feel like a public service rather than a rumour.
It is checkable in a way that appears to confirm it. Anybody can go and look at their tubes, and with four colours and a handful of tubes, some of them will appear to fit. A person who finds two matches out of three has, in their own experience, verified it.
And it is almost impossible to disprove casually. Demonstrating that the mark is a registration aid requires knowing something about tube manufacturing, which nobody has to hand during an argument. The claim wins by default because the correct answer is boring and technical.
The Real Information Is Printed in Words
What makes the myth faintly absurd is that the thing it claims to encode is already printed on the tube, in words, in a standardised format, because it is legally required to be.
The ingredients are listed. The active ingredient and its concentration are stated. Any claim about what the product does is regulated, and the warnings are there as well. If you want to know whether a toothpaste is a particular formulation, the information is on the box and the tube in plain language, in a format designed to be compared between products.
No manufacturer has any incentive to hide that information behind a colour code, and no regulator would permit a required disclosure to be made in a form only initiates could read. The whole premise requires an industry conspiracy to encrypt information that the same industry is already obliged to print in full.
Which is the general shape of a great many of these stories: a secret code carrying information that is, in fact, sitting on the label.
Where the Story Probably Started
Nobody can point to an origin for the colour-code claim, and the absence of one is itself informative.
Claims of this kind rarely have a first author. They assemble. Somebody notices the mark, somebody else offers a guess, the guess gets repeated with the hedging stripped out, a fourth person adds a detail to make it more specific, and within a few iterations there is a four-colour system with definitions, stated as fact, with no one who ever claimed to have invented it.
The specificity is the giveaway. A guess sounds like a guess, so a guess does not travel. A system with four defined categories sounds like information, and information travels. Each retelling has a small incentive to be more precise than the last, because precision is what makes the claim worth passing on – and precision is exactly what the original observation could not support.
That process also explains why the versions disagree. Search for the claim and you will find green meaning different things in different tellings, the list sometimes having three colours and sometimes four or five, and the categories varying between natural-versus-chemical and medicinal-versus-cosmetic. A real code would have one definition. A story assembled by accretion has as many as it has had enthusiastic retellers.
So the disagreements between versions are not evidence that some versions are right. They are evidence of how the whole thing was manufactured.
A Useful Test for the Next One
There is a reasonably good test for claims of this kind, and it takes about ten seconds.
Ask what the mechanism would be. Not whether the claim sounds plausible, but what would physically have to be true for it to work. In this case: who maintains the colour standard, how is it enforced across competing manufacturers in different countries, why would they agree, and what happens when a brand changes its packaging design?
None of those questions has an answer, and the absence is not a gap in your knowledge – it is the claim having no mechanism at all.
The same test disposes of most of this genre. The mark on the tube, the claim that a particular mark on a plastic container reveals a reuse count, the one about numbers on the base of a bottle indicating how many times it has been refilled, the one about the shape of a fruit sticker. In each case the mark is real, the function is mundane and industrial, and the explanation people prefer is the one that makes an ordinary object secretly communicative.
The Same Mark Is on Almost Everything You Own
The strongest argument against the colour-code story is that the mark is not peculiar to toothpaste.
Registration and position marks appear across packaging generally. A crisp packet has them, usually printed just inside the seal where the material is folded out of sight. A bag of frozen vegetables has them. A roll of cling film, a sachet of sauce, a blister pack of tablets, a tube of hand cream – anything made from printed flexible material that a machine has to cut, fold or seal in register with the design carries some kind of positioning mark.
Most of the time you never see them, because they sit in the part of the web that is trimmed off or folded into a seam. The toothpaste tube is unusual only in that the crimp leaves the mark on the outside of the finished product, in plain view, next to the part you hold.
So if the colours meant something, they would have to mean it across every one of those product categories, applied by every converter and printer in the supply chain, for products with nothing in common. Either that, or toothpaste alone has a secret system that happens to use exactly the same mark that everything else uses for an entirely mundane purpose.
Once you have seen the mark on a crisp packet, the story stops being plausible on its face, which is the quickest way to settle it for anybody who prefers evidence to argument.
What Is Genuinely Worth Knowing About the Tube
Since the colour square is a dead end, here is what the tube does encode, none of which is secret.
The crimp itself frequently carries a batch code and a date, stamped rather than printed, which identifies the production run. That is how a recall works, and it is the one genuinely consequential piece of information on that end of the tube.
The material matters more than the marking. Tubes are commonly a laminate of plastic layers, sometimes with a thin aluminium barrier, chosen so the contents do not dry out, do not react with the packaging and do not lose their flavouring through the wall. That laminate is why tubes were historically difficult to recycle, and why the move to single-material tubes that can go in with other plastics has been a significant piece of packaging engineering.
And the tube’s shape is deliberate: oval rather than round at the shoulder on many brands, so it does not roll off a wet surface.
All of which is more informative than a four-colour code that does not exist – and all of it is, as ever, a decision about the machine and the shelf rather than about the person holding it.
Go and look at a tube. Then look at the box it came in, where the ingredients are listed in full.
The square is for a photocell.
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