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By Dana McMahan

We all keep pretty close tabs on expiration dates for things in the fridge — well, most of the time anyway. After all, today's salad is tomorrow's science experiment so there's some built-in incentive. But it's not so simple to know when time's up on other things in the kitchen. Almost everything will need replacing sooner or later. But how do you know when?

Dish towels and sponges

When to replace them: Ideally, every day

We've heard the kitchen sponge horror stories. But what else should you be replacing, or at least swapping out for clean on the daily?

First things first. We need to step back and say germs aren't all bad, says biology professor Elizabeth Scott, Ph.D, co-director of Simmons Center for Hygiene and Health in Home and Community. “People talk about germs all the time, not knowing what we're talking about. What are germs? There are microbes that cause disease, there are other microbes that sometimes cause disease if they get in the wrong place at the wrong time. The vast majority of microbes don't cause disease but they've all been lumped together as germs. The media uses the term germ way too freely and people don't get it.”

That said, “yes, we need to understand that there are some pathogens we can protect ourselves against by practicing good hygiene,” Scott says, “but in such a way that we don't eliminate all the other microbes around us” Many of those microbes are not only beneficial, but critical, she says.

So, about that sponge. “The wetter the place the more bacteria there are,” Scott says. So “the kitchen sink really encourages bacterial growth.”

In an ideal world, replacing the sponge every day would be great, she says. But “another approach is keep it at your kitchen sink for washing up purposes [only] using hot, soapy water and decontaminate it on a daily basis. And weekly or biweekly it's time to replace it.”

Scott uses recycled paper towels instead of a sponge to wipe her counters, and says she would never use a sponge on something touched by a contaminant like raw chicken.

It's the same for dishrags and dishcloths. If you're cooking every day these items need to be swapped out for clean ones daily.

Cutting boards

When to replace them: When they look worn

Whether you have wooden, plastic or stone cutting boards, it's important to use one for prepping meats and another for vegetables and other items to avoid cross-contamination. They should be cleaned after every use using hot, soapy water to kill any bacteria. The USDA also recommends an extra step of sanitizing with a solution of 1 tablespoon of unscented, liquid chlorine bleach per gallon of water. If your cutting boards are excessively worn or have deep grooves that are hard to clean, it's time to toss them.

Your spice rack

When to replace them: 8 months to a year or two

How about that nutmeg that's been lurking in the back of your cabinet since the pre-iPhone era? The culinary experts at Serious Eats note the shelf life of a ground spice at about eight months, and whole spices for a year or two. You're in luck with the nutmeg they say; “some whole spices are so dense, woody, and intensely flavorful that they last for ages: think nutmeg and star anise.”

On the other hand, “some fine powders, like turmeric, black pepper, and ginger, lose all their punch in a flash,” and “dried herbs, flowers, and zested citrus don't age well.”

Your appliances

When to replace them: It depends

Appliances are among the biggest-ticket kitchen items. How long can we expect to hold on to them? Roger Beahm, Professor of Practice in Marketing and Executive Director, Center for Retail Innovation at Wake Forest University School of Business has some counsel. And the short answer is: until the next snazzy thing comes out.

Manufacturers focus less on durability now, he says, because they need to keep costs down — but also because they have to continually innovate.

It's not so much about how long a dishwasher or stove or fridge will last, he tells NBC News BETTER. Rather, where do you fall on the spectrum of adopting new technology? Manufacturers focus less on durability now, he says, because they need to keep costs down — but also because they have to continually innovate. “If you buy something and it's one and done, once you [the manufacturer] have penetrated 95 percent of households, you're out of business.” So they turn to upgrades meant to lure consumers to shiny and new every year.

Know thyself. If you want the latest bells and whistles, don't worry so much about longevity — buy what appeals to you now. Just know that something bigger and better will be out next year. If you don't need or care about smart appliances, on the other hand, “try to find items that are rated as most durable,” Beahm says. What constitutes durable? According to home warranty provider American Home Shield, “the average lifespan of major home appliances is around 10-15 years.” If you run into problems within that lifespan, “chances are fixing the specific problem and keeping it … will save you more in the long run.”

The pots and pans

When to replace them: 5 years for non-stick (even less if it starts to peel)

Yes, you may have heard about the grandma's cast iron skillet that lasted forever, but don't expect the bundle of non-stick cookware you picked up at the big box store to last anything like that. According to TheKitchn, you can expect about five years out of your non-stick pots and pans; it's time to retire anything with a surface that's pitted or starts to peel (to make sure it lasts that long, they offer some tips for taking care of them).

Are you looking around your kitchen thinking it's time to go shopping? I'll be right behind you.

Your Room-by-Room Cleaning Guide

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