D.W.
I am going to school to be an optician. the one thing that i can tell you is to change mascara's every two to three months. do not share eye make up with anyone because of potential risk of eye infection. mascara especially can harbor bacteria and give you a bad eye infection. as far as foundation it will get dry and cakey and after a year or so may tend to look yellow or not blend in right when you put it on. that foundation that is old is not harmful but will not be as fresh. if they stay in the original packaging and are not open they have a shelf life of 2 to 3 years.