Cosmetics do not all last the same amount of time. How a product is stored and used can affect its condition, so make a habit of checking both the label and the product itself.
Keep track of openings
Write the opening date on the package or in a note, and follow any manufacturer guidance. Wash your hands before applying products and keep containers closed. Eye makeup deserves particular care because applicators repeatedly come into contact with the eye area.
Notice changes
Discard products that develop an unusual smell, color or texture. The FDA advises stopping eye makeup use during an eye infection and discarding products used when the infection occurred. Seek medical advice about the infection.
Store with care
Keep lids closed and avoid leaving products in a hot car or direct sun. Do not add water or saliva to dried makeup. Follow the label and replace the product if you are unsure about its condition.
Further reading: U.S. Food and Drug Administration.