I'm not sure exactly when beauty product expiry dates came into play - apparently it was here in Europe that the concept was born, I'm guessing no less than 10 years ago but is important to take notice of the suggested use date.
I say suggested as certain products will be okay after the recommend use by date (the PAO date - period after opening), unless you are vigilant and note down exactly when you first opened a product, the chances of you never using a product past such date is slim. As a rule I check my products before use each and every time - particularly facial products. You know it is time to throw away any product if it has become discoloured, separated (not always nail polish, there's a reason there is metal balls in each bottle), changed in consistency or smell. If it is a facial product and suddenly feels very different on the face it is time to let it go. This can happen before the product in question has reached its PAO date.
PAO date? This is the period after you have first opened the product, it can be found on just about every product on the back and is symbolised by a round open tub. Inside the symbol you will notice a number followed by the letter 'M', this denotes how many months you have of suggested use. As you can see it widely differs give the category of product.Typically speaking water based formulations such as creams and liquids expire quicker than powders.
There are some general guide lines in each category, really you should always use your best judgement - of course if the product says longer than below, all the better. If you feel like something has changed in smell or consistency do not risk it. The one area you should be super vigilant with is eye products, no-one wants an eye infection or worse!
Lip Balm - Up to one year of use (keep in a dry, cool place to prevent it from melting and resetting constantly).
Lipsticks - Up to three years (same advice as above).
Lip gloss - Up to two years.
Lip Pencils - Up to three years (a tell tale sign it is past its best is when it crumbles or becomes beyond firm).
Mascara - No more than six months (if there is not a popping sound of air when you remove the wand it has dried out and should be disregarded. Never heat or add water to mascara to revive, all that does is encourages bacteria growth - gross.)
Powder Products - Up to three years (look out for signs of dampness and a smell change).
Skin and Body Care
Cleansers- Up to 18 month (look for product separation and scent change).
Toners - The exact same as above.
Moisturisers and Serums - Typically up to 1 year, more so when it is a body product.
Shaving Gels - Up to two years (when it stops foaming, it is time to let it go).
Shampoo and Conditioner - Up to a year (if I am honest I pay next to no attention in this category).
Sunscreen - Up to 18 months (another area to pay close attention to).
What product PAO date surprised you the most? For me it was Shampoo and Cleansers - as you rinse them off I assumed they'd have a longer shelf date.