For cosmetics with active ingredients, such as acne-fighting or anti-aging products, abide by the expiration date because the low concentrations of active ingredients can degrade quickly, said San Francisco dermatologist Richard Glogau. Other cosmetics that don't require expiration dates sometimes still carry them, often in the form of PAO (period after opening), a symbol of an open jar that suggests how many months you should keep the product after opening it. The biggest risk is microbial growth. If it doesn't look or smell right, it's time to dump, said Bailey.
Bill Hogan/Chicago Tribune