The Open Jar Symbol and the 12M/24M Number: How EU Regulation Dictates a Cosmetic Product's Maximum Period After Opening

That small open-jar symbol printed on the back of a moisturizer, containing a number like "12M" or "24M," is the Period After Opening (PAO) indicator. It dictates exactly how many months a cosmetic product remains safe to use once the seal is broken and the formula is exposed to air and bacteria [5]. While the European Union legally mandates this symbol under Regulation 1223/2009 for any cosmetic with a shelf life longer than 30 months [1], the United States Food and Drug Administration (FDA) requires no such post-opening safety timeline [4]. This regulatory divergence means that a consumer buying the exact same 36-month shelf-life serum in Paris and New York receives a legally mandated 12-month safety countdown in Europe, while the US buyer receives no mandated post-opening safety timeline at all.[1][4][5]

Two different clocks run on every cosmetic product manufactured today. The first is the total shelf life, which measures how long a completely sealed product remains stable while sitting in a temperature-controlled warehouse or on a retail shelf [3]. The second clock, the PAO, only begins ticking the moment a consumer unscrews the cap. Opening a product fundamentally changes its micro-environment, introducing oxygen, ambient bathroom moisture, and the bacteria naturally present on human fingers or applicators [5]. Without a preservative system capable of neutralizing these introduced microbes, a water-based emulsion quickly becomes a breeding ground for yeast and mold.[3][5]

The European Commission introduced the PAO symbol in 2005 and codified the requirement in Article 19 of the EU Cosmetics Regulation (EC) No 1223/2009 to address this specific secondary contamination risk [1]. The legislation operates on a strict 30-month threshold [2]. If a sealed product naturally degrades in 30 months or less, the manufacturer must print a "date of minimum durability," typically indicated by an hourglass symbol or the words "best used before the end of" [3]. This functions as a hard expiration date, regardless of whether the product has been opened.[1][2][3]

However, if the sealed product remains stable for more than 30 months, the hourglass is dropped. Instead, the manufacturer must display the open-jar PAO symbol, explicitly telling the consumer how long the preservative system can fight off contamination once the product is in active use [1]. This framework acknowledges that a highly stable sealed product is not immune to the biological realities of daily human use, ensuring that the safety countdown is explicitly communicated to the end user.[1]

In the United States, the regulatory framework shifts the burden entirely. As regulatory compliance firm Registrar Corp notes, "Currently, federal law does not require cosmetic manufacturers to print expiration dates on the labels of cosmetic products" [4]. Under the Federal Food, Drug, and Cosmetic Act, the manufacturer holds the legal responsibility for ensuring a product remains safe for its expected lifespan, but the agency does not mandate that this lifespan be communicated to the buyer [4]. Consequently, American consumers are left to monitor changes in color, texture, or odor to determine if a product has spoiled.[4]

Despite the lack of a federal mandate, many US-based brands voluntarily include the European open-jar symbol on their packaging. This voluntary adoption is driven by the logistical reality of global retail: a brand cannot sell its inventory in European markets without the symbol, making it cheaper to print a single, universally compliant label [2]. For products sold exclusively in the domestic US market, however, the symbol is frequently absent. This creates a fragmented landscape where some products offer precise post-opening timelines while others leave consumers entirely in the dark.[2]

The numbers inside the jar—most commonly 6M, 12M, or 24M—are not arbitrary estimates. To establish a legally defensible PAO in the EU, manufacturers must subject their formulas to rigorous Preservative Efficacy Testing (PET), often referred to as challenge testing [2]. During a challenge test, a laboratory intentionally inoculates a cosmetic sample with known concentrations of bacteria, yeast, and mold, such as Pseudomonas aeruginosa or Staphylococcus aureus. The sample is incubated at room temperature for 28 days, and scientists measure the decimal reduction time (D-value) to determine how rapidly the product's preservative system neutralizes the invading pathogens.[2]

The resulting PAO varies heavily by product category and water content. Eye-area cosmetics, particularly liquid mascaras and eyeliners, carry the shortest PAO durations—typically 3M to 6M [3]. The constant pumping of a mascara wand forces air into the tube, and the applicator repeatedly transfers bacteria from the eyelashes directly into the liquid, creating a high risk for severe ocular infections if used past its limit. Water-based skin creams and liquid foundations generally earn a 12M rating, while anhydrous products like pressed powders, lipsticks, and alcohol-based fragrances can maintain stability for 24M to 36M [5].[3][5]

Packaging design also dictates the final PAO number. Products housed in open-mouth jars generally receive shorter PAO durations than identical formulas packaged in airless pumps, simply because jars expose a larger surface area to the air and require the user to dip their fingers directly into the product [5]. To utilize the PAO system effectively, dermatologists and cosmetic chemists recommend that consumers write the opening date directly on the bottle with a permanent marker. Once the specified 12 or 24 months have elapsed, the product's preservative system is considered exhausted, and the item should be discarded regardless of how much formula remains inside.[5]