OK, so you're hungry and rooting around in the fridge, or maybe the pantry, and find something.
You think you've stumbled upon it - What's this? Chocolate? Yes! - when it dawns on you: You can't remember buying the bar. Or when you first opened it. What now?
Should you eat it or toss it?
What if it's milk? Or medication?
How long will that stuff keep, and what's at stake after you pass that point? For many things, your budget and personal preference can dictate how often you replace them, but for others, it's a safety issue.
Just about everything has a shelf life. Actually, two shelf lives: the time it will keep sealed in its airtight packaging and the time it will last after opening or being put to use.
Home air filters have a shelf life, as does beer, household cleaning products and cosmetics, which past their prime can breed bacteria and cause skin or eye infections.
While using something beyond its "use by" date typically isn't tragic, it's often not ideal.
Most salad dressing is still OK a few months after it's opened, but it probably doesn't taste the same as fresh. The same goes for condiments and coffee - even vitamins. They may not be as effective, but they're not toxic.
"Most likely the worst that would happen is that the product would start to go bad, spoilage bacteria would begin to grow, but not pathogenic bacteria," said Mark Kantor, an associate professor of nutrition and food science at the University of Maryland, College Park.
Where food is concerned, Kantor recommends you use common sense, along with some of the five senses (What's it look/smell like?) and keep your refrigerator clean and at the right temperature - between 33 degrees and 40 degrees Fahrenheit.
Medication is another matter. Manufacturer expiration dates signify the point at which the maker can still guarantee its drug is fully effective.In some cases, though - particularly with prescription drugs - lesser performance in itself can be hazardous.
"In many cases, especially for persons taking drugs for some fairly serious conditions - high blood pressure, diabetes - in these cases, if the drugs don't work, you could be in serious trouble from a health standpoint," said Frank Palumbo, director of the Center on Drugs and Public Policy at the University of Maryland School of Pharmacy.
The legislature requires pharmacists to give drugs a one-year expiration date, or less if recommended, when dispensing medication, regardless of what the manufacturer says. That means many drugs will probably last much longer than indicated, but - Palumbo cautions - it's not worth risking because you just don't know. And certain drugs do become toxic after a period of time.
An English company, called Timestrip, crafted a list of the shelf life of hundreds of products, consulting the U.S. Food and Drug Administration and dozens of manufacturers. It's something of a passion for founder Rueben Isbitsky.
Back in the mid-'90s, Isbitsky worked as a product manager for Brita, the water filter company, and he was obsessed with finding a way to get customers to change their filters every month or so, as they were supposed to.
A few years of research later, he'd turned the idea into a product and launched Timestrip - labels that can be attached to various products and keep track of time in multiple storage conditions.
They're available online (www.timestriponline.com) for about $15 for a pack of 50, though companies are beginning to incorporate them into their packaging. Hamilton Beach has built a Timestrip into an electric Febreze air freshener, and United Pet Group Inc. is about to add the technology to its Tetra Aquarium filters. Soon, Isbitsky hopes to expand into the world of vaccine and medication distribution.