You should never keep makeup too long, after awhile it starts to build up bacteria.
Here is some guidelines to how long you should have a product before replacing them!
Lipstick: Some experts say 1-2 years. Some say 4 years !
(If it smells, throw it out)
Lip glosses/chopsticks: 2 years
Powder eye shadow: 2 years
Cream eye shadow: 12-18 months
Eyeliner: 3 months
Mascara: 3 months (some last longer, smell it and if it stinks throw it out!)
Powder blush: 2 years
Cream blush: 6 months
Oil-free foundation: 12 months
Cream foundation: 18 months
Concealer: 12-18 Months
Lotions: 2 years
I hope these guidelines help you