Unlike food products, cosmetics usually don’t come with a precise expiration date. But there is a simple way to know the approximate safe period of time to keep and use makeup products.
“Period After Opening”, or PAO, is a type of expiration date that is printed on some cosmetics.
It looks like an open jar and can usually be found on the back, bottom, or side of the product packaging.
Inside the open jar symbol is a number followed by a letter, which is an indication for the length of time that the product is deemed safe to use from the date it was first opened.
For example, on a bottle of Giovanni Vitapro Fusion Leave-In Hair Treatment (see photo), the open jar symbol is accompanied by “24M”.
This means that this product is safe to use for 24 months or 2 years after its opening date.
PAO symbol only serves as a general guide for consumers and is not found on all cosmetics.
The PAO labeling is required on all cosmetics sold in the European Union (E.U.), which passed a law requiring such labeling in 2003 as part of the European Cosmetic Directive.
In the U.S. the PAO labeling is printed on any imported products or U.S. cosmetics that are manufactured by international companies that follow the E.U. requirement.
Connect with me: 
nice and very informative writeup keep it up. http://bit.ly/cciyP1