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Beginner's Guide to Period Underwear: Everything You Need to Know About Switching

Last Updated: July 13, 2022

Our primer on comfortable and leak-proof protection that’s both ecologically sustainable and economically smart.

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It’s called “free-bleeding,” and more women are doing it: Instead of managing period fluid with a menstrual cup, pad, or tampon, they’re grabbing period underwear specifically designed to be worn as a one-and-done solution to menstrual flow (or testing the waters with period panties designed to act as extra protection against leaks).


“Underwear only?” You might be thinking. You bet — and we’ll show you why.


Looking to navigate the various brands, materials, and need-to-know info for making the transition to period panties? We’ve got you covered.

Period underwear basics

woman on bed in black period underwear

What exactly is period underwear?

Period underwear are undergarments intended for you to wear during your period to take the place of disposable protection products like tampons or pads — although some women prefer to rely on period underwear only during lighter flow days, using them as backup during heavier flow days. Constructed to look and feel like regular underwear (i.e. not bulky), period panties are made with extra layers and special fabrics in the crotch area to absorb menstrual blood. Wash them, re-wear them, and wash them again — these are a reusable option all cycle long.

woman putting on jeans

How period panties work

Period underwear consist of an absorbent material that holds one to two tampons’ worth of flow, a moisture barrier to keep you comfortable, and a layer designed to prevent any leaks or staining. Still hesitant to make the switch and entrust your flow completely to underwear? Many users first start with lighter flow days or using their period underwear as backup protection before graduating to full-time use.

“A great way to give period underwear a try is to wear it overnight towards the end of your period when your flow is lighter,” says Meika Hollender, co-founder and president of Sustain, which offers period underwear made from 95% third-party certified organic cotton and 5% spandex, with a lining of polyurethane laminate topped with organic cotton. “Additionally, trying it out as a back up on a heavier day is great too!”

two women in tops and black period underwear against red background

Why make the switch to period underwear?

Beyond the comfort factor and leak-proofing, period panties are also gaining popularity as both an ecologically sustainable and economically smart choice. Try them if you’re looking for a solution less irritating than tampons, more comfortable than sanitary pads, and less messy than using a menstrual cup. And with period panties, you’re always ready: No more frantic late-night tampon runs to the corner store.


Looking for a real review from someone who made the switch? Read this Grove writer's take on Sustain's period underwear and how it works.

Top reasons to switch to period underwear

2–5 years

How long period underwear can be washed and reused, “as long as you wash them by hand with cold water regularly,” says Hollender.

woman putting jeans on over period underwear

So ... does period underwear actually work?

Yes! Period underwear are designed to replace your use of pads and tampons. They can replace liners, pads, tampons, and cups, or be worn with a tampon or a cup for extra protection.

Can you wear period underwear all day?

Depending on what type of period underwear you have and where you are in your cycle, you might be able to wear a pair of period underwear all day. You can usually buy heavy, medium, or light flow versions of most period underwear. If you wear period underwear as extra protection on your heavy days (with a tampon or menstrual cup), it'll be easier to wear the underwear all day. On light days, it's likely you'd only need one pair of underwear to last the day.


Grove Tip

What's the deal with PFAS?

Short for per- and polyfluoroalkyl substances (say that three times fast), PFAS have been shown to be harmful to human health even at low concentrations, and have been associated with cancer and decreased fertility. While some period underwear brands tested positive for PFAS, Sustain's underwear underwent an independent lab study that confirmed the product was PFAS-free.



“From day one, Sustain has advocated for better ingredient transparency and regulation for menstrual hygiene products,” says Hollender. “Additionally, since we launched, Sustain has always listed 100% of our product ingredients on our website and packaging. We're happy to see confirmation that our period underwear is PFAS-free.”

Period underwear pointers

Finding the right fit

No need to worry about looking like you’re wearing the equivalent of an adult diaper; most brands offer two sizes to meet your lighter or heavier flow needs. They’re also offered in a wide variety of colors and cuts, from ultra femme, lacy thongs to more gender-neutral boy shorts. If you’re looking for a bikini-style panty, Sustain has a selection of sizes in chic black organic cotton. Want to swim? RubyLove offers a period-protection swimwear line. For the younger set, Thinx have specifically tween- and teen-designed period panties in a selection of smaller sizes and fun colors.

How many pairs of period underwear do I need?

If you’re first trying them out, you’ll probably want several pairs to replace your traditional period products on your lighter days. If you decide to commit, you’ll likely want a full five- to seven-day set depending on the length of your flow, so you’re not laundering every other day. You can also consider a sleep-specific pair or two: If you want to sleep worry-free, look for a cut that fits a little more snug (go for stretchy fabrics) with extra coverage for side and rear leak protection.

How to care for period underwear

Step 1: Soak

After you remove your period panties, drop them in cold water to soak or rinse them.

Step 2: Wash

If machine washing, first place them in a washable mesh bag and wash on the delicate or gentle cycle. To make your underwear last, consider hand-washing with a mild detergent.

Step 3: Dry

Do not put in dryer. Instead, lay underwear flat or hang dry to help maintain the fabric's integrity.

Step 4: Treat

Worried about stains or lingering smells? Period undies are designed to be stain-resistant and shouldn’t retain a scent if cared for properly, but you can soak them in vinegar/water mixture prior to laundering, too.

Period underwear tips & tricks

two women in period underwear

Is period underwear a solution for my leaky bladder?

Generally, no, although Thinx has developed Speax, a line specifically for bladder protection.

Can I use period underwear for postpartum bleeding?

Yes. During the initial postpartum period, you may want to pair them with pads.

Can I swim in period panties?

You can find period swimwear specifically designed for this. In general, though, you’re best using a cup or tampon and saving your period panties for dry land.

Shop period underwear

Ready to give period underwear a try? Pick up a pair of Sustain's Period Underwear. Available in five sizes, our organic cotton period underwear are a reusable alternative to tampons and pads. They absorb up to 1 tampon's worth of blood, and can be washed and re-worn again and again. Use as a replacement for disposable products or as a backup. Even better? One percent of every Sustain purchase goes to our 1%4Women fund that supports women’s health organizations in the U.S.

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