Here's When to Replace Common Household Items

NOTHING lasts forever.

Air Filters

Replace after: Six months
Why: Filters become clogged with dirt and other particles, reducing the energy efficiency of your heating and cooling systems, says Rozanne Weissman, a spokeswoman for the Alliance to Save Energy.

Computers

Replace after: Four years
Why: Unless you're using your computer for very basic functions (i.e., word processing), technology will have likely advanced enough that you need a significant upgrade, says David Carnoy, executive editor of CNET, a technology review web site. Rather than trying to put a new processor into an old computer, you're typically better off buying new. "With laptops, there isn't much you can do to upgrade them," he says. Upgrading your desktop is possible, but unless you're a technology whiz, that process can be as expensive as buying a new computer (and infinitely more complicated).

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Cosmetics

Replace after: Three months to two years
Why: Microbe growth in makeup can cause skin irritations and infections, explains Paula Begoun, author of "Don't Go to the Cosmetics Counter Without Me." The worst offenders are liquid cosmetics, which build up bacteria more quickly. Keep mascara for a maximum of three months; other liquids and creams (eyeliner, foundation) for no more than a year. Powders (eyeshadow, blush) can be used safely for up to two years.

Fire Extinguishers

Replace after: 10 to 12 years
Why: The pressurized contents of a fire extinguisher de-pressurize over time. "Eventually, it just becomes a block of 'stuff' inside the cylinder," says Tom Olshanski, director of external affairs for the U.S. Fire Administration — rendering it useless in fighting fires. Extinguishers can deteriorate faster if left in a high-humidity environment. Check your extinguisher on a monthly basis for corrosion, a sure sign air is leaking out, he suggests.

Mattresses

Replace after: Seven years
Why: Mattresses wear out over time, says Kathleen Huddy, textiles director for the Good Housekeeping Institute. One that sags or is uneven won't keep your spine in line as you sleep, which means you may have trouble sleeping. It's likely you'll also experience neck and back pain while awake. There's also an ick factor to old mattresses, she explains — they collect dust, dirt and allergens that can't be removed.

Perfume

Replace after: Two years
Why: Exposure to light, heat and air lighten and alter perfume notes, explains Andrea Walker, a makeup expert with Sephora. "It weakens the scent," she says.

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