Don’t store makeup in your bathroom. Bacteria and airborne microbes breed in bathrooms, and will no doubt get into your makeup.
Avoid makeup sharing. It is unhygienic to share makeup with someone else.
Store all cosmetics in a cool dry place, out of moisture and the sun.
Always re-cap after use. Keep containers properly sealed.
Cosmetics cannot last forever because they have due dates too. Throw them away once their time is up.