Two markings, one of which applies
Cosmetic products in the United Kingdom carry a durability marking, and it takes one of two forms depending on how long the product is expected to keep.
Where the minimum durability is thirty months or less, the pack carries a date of minimum durability, introduced by wording such as best before end, and often accompanied by an hourglass symbol pointing to where the date is printed.
Where the minimum durability exceeds thirty months, a date is not required and the pack instead carries a period after opening: an open jar symbol with a figure such as 12M, meaning the product is expected to remain suitable for twelve months after it is first opened.
Only one applies to a given pack, and which one it is tells you something in itself: an open jar symbol indicates a product expected to keep for more than thirty months unopened.
What the date measures
The date of minimum durability is the date until which the product, stored under appropriate conditions, continues to fulfil its initial function and remains compliant.
Two phrases in that sentence do a great deal of work. Stored under appropriate conditions means the storage the manufacturer specified, which is why packs carry storage instructions. And continues to fulfil its initial function, for a sun protection product, means continues to deliver the protection it was tested for, which is the reason the marking matters more here than for many cosmetic categories.
The date is derived from stability testing, in which samples are held under defined conditions and assessed over time. It is a projection based on controlled storage, not an observation of the particular pack in your bag.
What the period after opening measures
The period after opening is a duration, not a date, and the clock starts when the product is first opened. It reflects the point at which the manufacturer expects the product to remain suitable for use once exposed to air, to fingers and to whatever is in the room.
Its obvious weakness is that nobody records when they opened a pack. The marking depends entirely on the user's memory, and for a seasonal product picked up once a year that memory is unreliable.
Its less obvious weakness is that it measures from opening, so it does not account for a long period in storage before opening, or for storage conditions after it.
| Date of minimum durability | Period after opening | |
|---|---|---|
| Applies when | Minimum durability is thirty months or less | Minimum durability exceeds thirty months |
| Form | A date, with wording such as best before end | An open jar symbol with a number of months |
| Symbol | An hourglass, pointing to the date | An open jar |
| Clock starts | At manufacture | At first opening |
| Depends on the user remembering | No | Yes, entirely |
| Accounts for storage conditions | Assumes those specified | Assumes those specified |
Framework of this publication. It describes how published rules and guidance fit together and is not a measurement, a survey or a study.
Why this matters more for sun protection
For most cosmetic products, a product past its durability marking is a matter of texture, scent and microbiological quality. For a sun protection product there is an additional dimension: the product is bought for a measured performance, and the marking is the manufacturer's statement of how long that performance is expected to hold.
Ultraviolet filters are chemically active substances in a formulation designed to hold them in a stable arrangement. Emulsions separate, formulations change and filters can degrade. None of that is visible from outside the pack, which is the point: a product can look and smell entirely normal and no longer be the product that was tested.
That is why the marking should be treated as information rather than as a suggestion, and it is also why the storage conditions examined in heat, storage and what degrades a sunscreen matter alongside it.
The seasonal problem
Sun protection has a use pattern almost no other cosmetic category has. It is bought in a burst, used intensively over a short period, and then put away for most of a year, frequently somewhere warm.
That pattern interacts badly with both markings. A date of minimum durability may pass unnoticed while a pack sits in a drawer. A period after opening runs through months in which the product is not being used at all. And the storage during the dormant period is often the worst it experiences, because a bag left in a car boot or a cupboard against an external wall is not the storage the stability testing assumed.
The practical implication is not a rule, and it is not this publication's place to issue one. It is that a durability marking on a seasonal product is doing more work than the equivalent marking on a product used daily, and deserves more attention rather than less.
Finding the marking
Both markings are frequently printed rather than included in the artwork, which means they are inked onto the pack, sometimes on the crimp of a tube, sometimes on the base, sometimes on the shoulder, in a small typeface and often in a colour close to the substrate.
The hourglass symbol exists precisely to point at a date printed elsewhere on the pack. If you see it and no date beside it, the date is somewhere else on the packaging.
For a product in a carton, the marking may be on the carton, the container or both, and discarding the carton can discard the date.
The batch number, and who it is for
Alongside the durability marking sits a batch number or reference identifying the product. It is required, it is usually printed rather than in the artwork, and it is meaningless to a reader.
That is not a complaint. The batch reference exists so that a specific production run can be identified: by the manufacturer for quality investigation, by the responsible person for tracing a complaint back to a batch record, and by an enforcement authority establishing what a product on a shelf actually is.
Where it becomes relevant to a consumer is in a withdrawal or recall, where a notice will identify affected batches rather than an entire product. Keeping the outer packaging until a product is finished is the practical implication, since the batch reference is frequently on the container in tiny print and on the carton more legibly.
It is also, indirectly, the mechanism by which a test report ties to a real product. A determination relates to a formulation, and a batch record ties a shelf pack to that formulation. Without it, the connection between an unpublished test and a physical product would be an assertion.
What the markings do not tell you
They do not tell you how the pack was stored between the factory and the shelf, or between the shelf and now. They do not tell you whether the product has been through a heat cycle that the stability testing did not anticipate. They do not tell you what the actual protection is now, because nobody retests a pack in use.
And they do not tell you when the product was manufactured, which is a genuine gap for a period after opening marking on a seasonal product. The batch number identifies the production run and is meaningful to the manufacturer, not to a reader.
What the marking means for a retailer
Durability markings carry obligations further up the chain as well, and it is worth naming them because they explain the practice of clearing seasonal stock.
Distributors have their own duties under the cosmetics regime, including acting within their activities with due care in relation to the requirements, checking that the required labelling is present, and taking account of the date of minimum durability where one is shown. A product on a shelf past its stated date is a compliance matter as well as a quality one.
That obligation is easier to discharge for a dated product than for one carrying a period after opening, since nothing on an unopened pack with an open jar symbol tells a retailer how old it is. The batch reference does, to the manufacturer, which is one reason stock rotation in this category runs on batch records rather than on what is printed for consumers.
What to take from this
A date where durability is thirty months or less, a period after opening where it is longer, and only one of them on any given pack. Both are projections from stability testing under specified storage, and neither accounts for the car boot.