I've argued for showering infrequently, washing your towels less, and changing your sheets more often than the average numbers floating out there in the webiverse. Clearly, I thought I had this life stuff figured out. But now a new question has me stumped: When should you throw old undies out? (Conversely, dear reader: When should you buy new skivvies?) 

I'm honestly not sure. I mean, I definitely get rid of them when they have holes or stains, that part is easy. 

When it comes to how often you should replace your underwear, I don't think there's a hard-and-fast rule, because if you're like me, you have many pairs of undies and certain ones only get worn with certain pants, meaning they are worn infrequently, while others are in regular rotation because they're the most comfortable. I definitely wear different bras in the summer and the winter — so some of my bras are more than 5 years old but I don't want to throw them out as they are still in great shape. 

You might hear some people say "Replace all your underwear once a year," but while I want to be clean and respectable, I also don't want to be wasteful. I'm not that hard on my underwear (and I wash it in net bags in my regular wash on cold and hang it to dry) so it will last for as long as possible. We need guidelines here, not rules. So let's figure this out: 

1. Get comfortable

OK, first things first. If your underwear doesn't fit or isn't comfortable, toss it. Period, the end, no arguments. Life is difficult and complicated enough without wearing ill-fitting items on your intimate parts. And if it's uncomfortable, it tends to be unflattering too, so don't even debate this one.  

2. Be prepared

Next, I'd say (being practical): Make sure you do have appropriate cuts and colors of underwear to work with all your clothes. Ruby Brallier of lingerie company Skarlett Blue advises, "You’ve tried to wear that new white dress three times and it keeps ending up in the 'no' pile on the floor because your go-to bra screams 'cheetah.' Make sure your intimates match your wardrobe – or at the very least, don’t show right through. The perfect solution for this? Stock up on neutrals!"

For guys, that means that you need white, grey and black undershirts and if you wear boxers, you should have some briefs or trunks to wear under more formal/slimmer-cut clothes.

For ladies, that means at least one smooth, skin-toned bra. (Notice I don't say "nude" or "white" bra here for a reason — if your skin is dark, a white bra will be obvious, and if you are super-pale, a "nude" bra won't be. Try NubianSkin for dark skin tones or these recommendations for various skin tones). Basically, you want one bra and a couple pairs of underwear that matches your skin tone and doesn't show underneath clothing. Kill two birds with one stone and get a skin-tone bra that has detachable straps so you have a go-to bra when you need a strapless one. Plain black undies and a bra are also imperative for wearing under darker-colored clothing. 

If you don't have these basic items, put them on your list. 

3. You've changed partners

"You have a new significant other in your life – you’ve traded up partners, now trade up on lingerie too," says Braillier, which is definitely smart. I remember getting rid of a lot of things (including underwear!) when I broke up with my ex and started my single life. It's a great time to start fresh. You are kind of a new person when you are single again, so your foundational pieces should reflect that.

4. If they smell

OK, I hate to get personal here, but both bras and undies can look OK, but can pick up weird odors along the voyage of life. It might not even be your fault! I'm not just trying to make you feel better — pieces that contain polyester can actually grow a special type of particularly smelly bacteria that can be transported from one item (say, a sweaty sports bra) to another (a pair of knickers) in the wash. (I know, life is so unfair isn't it?)

So give your stuff the smell test. This goes for bras for ladies and underwear for both genders. Polyester can easily look great — and smell terrible. And no, there is nothing you can do to get that weird bacteria smell out. You could try hanging it in the sun, which I have used with some success on sports bras short-term — but that smell always comes back. 

4. You haven't updated in 5 years

So much has happened in underwear — for both men and women — in the last few years. Guys, if you haven't tried boxer briefs (or variations like trunks and sports trunks), you are missing out — or so my guy friends and partner have told me. There are more fits and lengths and materials (like super-soft organic cotton) than ever before, and especially if you like wearing skinnier pants, you can find underwear that might be significantly more comfortable than your old standbys. Sport trunks in wicking fabrics for working out, super soft wool boxer briefs to keep your butt and thighs warmer when it's cold out, and heavier-duty silk boxers have all been improved over guys' traditional underwear choices of boxers or briefs. 

Ladies, there has been an explosion in bras and camisoles. I've stopped wearing underwires entirely, because the new soft-cupped halter bras, cropped bras and bralettes are so incredibly cute and comfortable. Free People even makes a "brami" which is a cross between a bra and a camisole and it's my favorite thing ever. And have you tried a racer-back bra yet? They are NOT just for sports bras anymore and they are also the best.

Yes, the former bras are generally more comfortable for smaller-busted ladies (so my larger-busted friends tell me), but there are also many more options for the more bosomy. Just take some time to see what's out there and stalk the sales — plus most sites will give 10 to 20 percent off for first-time customers, which is a lower-risk way to try something new. 

If you haven't bought new underwear in 5 years — and that's not as uncommon as you might think — consider replacing at least half of what you have with some new cuts, fabrics and styles. You might just find something that works much better for you! 

What about you? How do you decide it's time for new underwear? 

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Starre Vartan ( @ecochickie ) covers conscious consumption, health and science as she travels the world exploring new cultures and ideas.