Jenny Chang / BuzzFeed It's pretty easy to know when things like milk and eggs go bad. And other things, especially foods, have clearly marked expiration dates on their packaging. Jitalia17 / Getty Images But here we're talking about products that don't always have a listed "expiration date," but will lose their effectiveness over time. Thinkstock Some things, like car seats and potatoes, can actually be dangerous once they pass their usefulness date. Other things, like sunscreen and bleach, will just stop working after a certain time. And others, like razors and mascara, can start to grow bacteria after being used a number of times.The U.S Food and Drug Administration (FDA) doesn't actually require manufacturers to list expiration dates in the U.S. And even listed expiration dates are just "rules of thumb" according to the FDA: any product's effectiveness and safety depends on both the consumer's knowledge of the actual date of manufacturing and the proper storage. 1. Potatoes Joerg Mikus / Getty Images The common potato and other plants of the same nightshade family (like tomatoes and eggplants) contain traces of a toxic chemical called solanine that can be very dangerous and even deadly. The toxin is minimal in raw, unspoiled potatoes, but if sprouted, overexposed to the sun, or stored near other vegetables that increase spoilage (like onions) for a long period of time, the concentration of this chemical can become harmful. When stored correctly, ripe potatoes should stay good for two to three months. Solution: Don't eat green (unripe) or sprouted (overripe) potatoes; store potatoes in a cool, dark place. 2. Bleach (and Other Disinfectants) Lana Langlois / Getty Images Bleach loses some if its potency around three months. This shouldn't be a problem for household laundry, but the disinfectant qualities fall below the EPA standards around this time, which means it isn't effective for cleaning. Solution: Toss your bleach every few months or so. Same goes for Lysol and other household disinfectants. 3. Sunscreen Farakos / Getty Images According to the Mayo Clinic, most sunscreen works at full strength for around three years. Solution: Throw out sunscreen past the listed expiration date. If it doesn't have a date on the bottle, just note the day of purchase and toss after a few years. 4. Power Strips and Surge Protectors Helder Almeida / Getty Images Cheap power strips or ones that have been overworked can be a fire hazard, and use a lot of energy in your house. Even good-quality surge protectors are only designed to last for a certain amount of joules, which is the amount of excess electrical surges they absorb. Neither products typically come with an expiration date, but the product warranty is a good way to gauge how old they are. Solution: Only buy surge protectors and power strips with a UL or OSHA rating, and if they start to get discolored or hot to the touch, get a new one. It's generally a good idea to replace them every couple of years just to keep you (and your electronics) safe. 5. Spices Svetl / Getty Images Dried spices often last for two to three years, but it depends on the kind, how they were dried, and how they are stored. Solution: Refer to this chart of how long different spices last. 6. Fire Extinguishers Antos777 / Getty Images Most fire extinguishers don't expire for five to 15 years, depending on the type, but things like cracks in the hose and the pressure can affect how well they work. Solution: Check the pressure in the gauge often, and make sure to recharge (aka refill) after any use. 7. Car Seats Ryan Mcvay / Getty Images Because they are made from materials that expand and contract with age and temperature, and the car itself changes temperature so frequently, most car seats expire six to 10 years after their manufacture date, which should be stamped somewhere on the bottom or side. Previous damage or car crashes can also affect the safety of the seat, which is why it isn't a great idea to buy a used model. (For more info on buying or selling a seat, go here.)Solution: Check for the expiration date on the individual model and don't buy used versions unless you know the history. If you're uncertain, there are car seat inspection stations that will check the seat for you. 8. Mascara Adisa / Getty Images Bacteria (like the kind that causes pinkeye and other infections) can start to grow in an open mascara tube within three months of use. Plus, with lots of pumping, the product will begin to dry out around the same time. Some products even have a hidden expiration date. Solution: Buy new mascara every couple of months, and don't share with anyone else. 9. Loofahs Trinaestipo / Getty Images Sponges and natural loofahs can start to breed bacteria in just a couple of weeks. Plastic mesh loofahs (like the one pictures here) are safe a little longer, up to eight weeks. Solution: Rinse and dry all your loofahs after each use. Replace natural loofahs every couple weeks, and mesh ones every other month. 10. Batteries Gilles Paire / Getty Images Batteries start to expire as soon as they're made, so the expiration date printed on them or the package is based on this and not when or how they're used. The shelf life differs between types and sizes of battery, as well as where they are stored. Solution: Store batteries in a dry, room-temperature location, and check the date. 11. Smoke Detectors Tab1962 / Getty Images Smoke and carbon monoxide detectors can stop working after 10 years, even if the batteries are replaced. Solution: Most should have the expiration or manufacture date listed somewhere on them, but if you move into a new home and don't know the age, it's safer just to replace them. 12. Liquor Isabel Da Silva Azevedo Drouyer / Getty Images Unlike wine, which continues to age even in the bottle, unopened liquors will stay good indefinitely. But an opened bottle of liquor will begin to lose its taste and potency after about a year. But unless you're a connoisseur, you probably won't notice a big difference until much later. Solution: Keep opened and unopened bottles in a cool place. 13. Lotion Kasiam / Getty Images Lotions and moisturizers in a tube should be good for a couple of years when opened, and after that will start to dry out and lose their effectiveness. But lotion in a jar that you use your fingers to apply can become a breeding ground for bacteria even sooner.Solution: Use clean hands to apply lotion, and toss after a year or so. 14. Hydrogen Peroxide Jupiterimages / Getty Images When it's opened, hydrogen peroxide only lasts a few months before it becomes ineffective (aka turns to water). Unopened, it should be tossed after a year. You'll know when it's bad when it stops fizzing.Solution: Toss everything and get a new first aid kit every couple of months, especially if it's been used. 15. Lipstick Top Photo Group / Getty Images Lipstick that's exposed to air starts to dry out and change consistency after around two years. You should be able to tell by a change in smell and texture. Some products also have a hidden expiration date. Solution: Past the expiration date or after two years, any lipstick that's been opened should be tossed out. It's also smart to give your lipsticks a good cleaning every once in a while. 16. Insect Repellent Rene Drouyer / Getty Images Insect repellent loses effectiveness after around two years from the manufacture date, which should be marked on the bottle. Don't let the bugs win. Solution: Check the date before you buy to make sure it isn't already old, and get new spray every couple of years. 17. Running Shoes Trinaestipo / Getty Images After around 250 miles of running, sneakers can start to lose their cushioning, which means more stress on your joints. Solution: For hard runners, get new shoes every 200 to 300 miles. For less strenuous users, replace your workout shoes every six months to a year. 18. Disposable Razors Trinaestipo / Getty Images Sure, you know that disposable razors are supposed to be disposable. But do you know how often? To prevent bacteria buildup and razor burn, you should toss your razors every week, or every three to four shaves. Solution: Get a new razor every week, and make sure to let it dry between uses. 19. Bike Helmets Helder Almeida / Getty Images Like car seats, bike helmets can lose their safety effectiveness over a couple of years and after any kind of crash or trauma. Solution: Replace helmets if they've been damaged in any way, and otherwise replace every three to five years or based on manufacturer recommendations. Pro tip: Use permanent marker to write the day of purchase on anything you have that might expire. Better Homes & Gardens / bhg.com That way you'll know at a glance just how long something's been in your house. If it's a food item with an expiration date, write it in bigger, easier-to-read print so you'll know exactly when to toss it.