“12M symbol”: This mark on the tube indicates whether your sunscreen from last summer is still usable
Every time summer begins, the same doubt creeps up from the bottom of my beach bag: that tube of sunscreen I found left over from last summer still effective? The answer depends on several concrete indicators, and one sign in particular—clearly visible on the packaging—makes all the difference.
The first thing to look for on a tube of sunscreen
On any sunscreen product, there is a small pictogram that deserves your full attention. It is the Shelf Life After Opening (SLAO), represented by a small open jar followed by a number: “12M” or “18M.” Most tubes indicate “12M,” which means the product must be used within one year of first opening.
So, if you opened your bottle last June, the theoretical expiration date is this June. After that date, the UV filters degrade and the actual SPF drops, without any visible signs of deterioration.
However, the phrase “best used by” applies only to unopened tubes. As long as this best-by date has not passed, an unopened tube of sunscreen remains usable in principle.
What the UFC-Que Choisir study says about actual lifespan
To investigate this further, UFC-Que Choisir conducted a 14-month study of eight sunscreens. The products were subjected to alternating cycles of cold, intense heat, and artificial UV radiation. At the end of the study, six of the eight products remained stable.
“So you can use a sunscreen that still looks normal a year later. However, using it for three summers in a row would probably be excessive. ” — UFC-Que Choisir
These reassuring results do, however, have a significant limitation. Organic sunscreens with mineral filters were not included in the study, which means we should remain vigilant when it comes to these formulas.
The exception that calls for the greatest caution when it comes to sunscreen
Some sunscreen products containoctocrylene, a chemical UV filter found in many traditional formulas. This filter poses a particular problem over time.
According to Laurence Coiffard, a professor and researcher in cosmetic formulation at the University of Nantes, this filter “becomes carcinogenic when it breaks down over the long term.” Furthermore, she points out that “this degradation is completely invisible, and consumers have no way of knowing it’s happening.”
Therefore, for products containing octocrylene, checking the use-by date is not enough. It is best to replace the tube every season, without exception.
Visual and olfactory signs that indicate a product has gone bad
Beyond the expiration dates, the appearance of the product itself provides valuable clues. A safe sunscreen has a uniform texture, with no separation between its components. If oil separates from the cream, or if lumps appear, the product has gone bad.
Smell is also a reliable indicator. UFC-Que Choisir is clear on this point: “If the product smells rancid or has any other suspicious odor: throw it away!” There’s no point in trying to test it on your skin in this case.
- Check the Shelf Life After Opening (SLAO): “12M” means 12 months after opening.
- Check the best-by date on unopened tubes.
- Check the texture: If a cream has separated or has lumps, throw it away.
- Smell the product: A rancid or suspicious odor indicates spoilage.
- Look for any changes in color: unusual yellowing or browning indicates chemical degradation of the filters.
When a product’s color becomes a warning sign
Another visual indicator deserves attention: color. Unusual yellowing or browning—especially in white formulations—indicates chemical degradation of the UV filters. This change may seem minor, but it signals actual degradation.
In this case, sun protection becomes unpredictable. The skin may then be exposed to much more UVA and UVB radiation than expected, without you realizing it at the time. However, the WHO emphasizes that repeated sunburns significantly increase the risk of melanoma.
Therefore, even a tube that looks normal deserves a close inspection before being put back into service. Date, texture, smell, and color are the four key factors to check before each summer season.
