Updated: Jan 16, 2019
We reviewed the information on the label in our earlier post. Let us look at two important instructions in detail:
Expiration Date/ Shelf life 
A product’s expiration date or shelf life is essentially, the period it is safe to use and will perform its function. Depending on the type and nature of the product, an expiration date can vary. This depends on number of factors:
Overall stability and performance of the product (drying out of mascara or nail polish, foul odour in creams)
Preservatives and their concentration
Nature of packaging material (unit packs like sachets or jars or tubes)
Where and how the product is stored (temperature and exposure to light)
Change in physical properties (consistency, stability, separation, oil or water oozing)
Based on Regulation EC 1223/2009 of the European Cosmetics Legislation, if a cosmetic product has a shelf life of less than 30 months, an expiration date must be clearly indicated on the product’s packaging. In cases where the shelf life exceeds 30 months an expiration date is not required to be placed on the packing, however a period after opening (PAO) is.
Period after opening 
The PAO correspond to the period during which the product is stable after opening and can be used without any risk to human health or loss in performance. PAO is originated within the European market & applies only for products having shelf life more than 30 months. It is denoted by an open jar symbol with time mentioned in months (M).
Example: Expiration date is printed on a package, e.g. Expiry: 05/18, and PAO is also printed: 12M. In such scenario, in any case you should stop using this product after 05/18. You should throw out this cosmetics after May 2018.
But if PAO will be reached before the expiration date, this also can mean your product has been expired. For example, If Expiry is 05/18 & PAO is 6M. If you opened the cosmetic product on 16.08.2017, PAO will be reached after 6 months (6M), i.e. 16.08.2017 + 6 months = 16.02.2018; in Feb 2018, your product will be expired and unfit for use.