Research shows that most women are using makeup that has long past its sell by date - out of date make up can cause many diseases - generate germs - damage your health and your looks - mascara for example should only be kept for 4-6 months - most women keep it for 12 months - the list is long - is your make up - up to date?
I make my own mascara fresh, every couple of months. I don't wear makeup otherwise, unless I'm going on stage. But yes, I used to work in a laboratory and have run all kinds of tests on all kinds of consumer products. It's not just the bacteria you have to worry about growing there after you open your makeup, either.
Make up should be always up to date. More than up to date it should be from a reputed brand. Cheap and old make up items are the biggest threat for your skin. Ensure if the products are dermatologically tested and recommended. Do not preserve or store these make up items for more than 6 months.