How Does Period Underwear Work?
In the world of menstrual products, period underwear has been described as a revolutionary game-changer. What’s not to love about a product that claims to calm the panic of heavy flow days or the realization that you’re out of tampons?
If you’ve ever wondered how period underwear actually works, you’re not alone. From how it absorbs blood to how long you can wear it, this guide explains exactly what’s happening inside the fabric and whether period underwear is effective for real life.
What is period underwear?
While it looks like conventional underwear, period underwear is a washable, reusable menstrual hygiene product made of layered absorbent material, such as microfiber polyester, nylon, lycra, cotton, or bamboo. You can use it as an alternative to other period care products, or use it alongside tampons or menstrual cups.
The absorbent material that period underwear is made from captures blood flow—some pairs can hold three regular tampons’ worth of liquid—and prevents leaks.
How does period underwear work?
The magic of period undies lies in their layers (typically three) placed in the crotch area. Let’s look at what they are and how they work:
Moisture-wicking top layer
As you bleed, this topmost layer quickly wicks the blood away from your skin and into the layers of the underwear. This leaves you feeling dry for as long as you wear the period panties, even if your flow is heavy and comes with clots.
Absorbent middle layer
This is where the top moisture-wicking layer sends your menstrual blood to collect. Different period undies have different levels of absorbency, catering to light, medium, and heavy flows.
Leak-resistant barrier
The final layer is made of leak-proof materials and creates a shield to prevent the blood from escaping. This keeps your menstrual blood safely locked inside the absorbent layer. That means you’ll no longer have to keep checking your clothes for stains.
In addition to these layers, many period undies have built-in antimicrobial protection and odor control. This prevents the growth of unwanted bacteria that may cause infections, and stops your panties from smelling.
LOLA’s period underwear holds up to three tampons’ worth of fluid and is designed for all-day comfort. [Shop now]
How much blood can period underwear hold?
Typically, period underwear can hold anywhere from 5 ml to 50 ml of menstrual blood, although there are ones that can absorb more.
- Period panties designed for light flow: Absorb up to 10 ml of blood, equivalent to 1-2 tampons or pads
- Period panties designed for medium flow: Absorb up to 20 ml of blood, equivalent to 3-4 tampons or pads
- Period panties designed for heavy flow: Absorb up to 30 ml of blood, equivalent to 4-5 tampons or pads
- Period panties designed for super heavy flow: Absorb up to 50 ml of blood, equivalent to 5-7 tampons or pads
How long can you wear period underwear?
While the duration depends on your flow and comfort level, you can typically wear period underwear for up to 8-12 hours. We don’t recommend wearing it for longer than that, as it can lead to leaks, irritation, and bad odor.
Can you wear period underwear alone or with other products?
While period undies are designed to replace other menstrual products, you can also wear them as a backup with other menstrual products, such as tampons or menstrual cups, especially overnight or on heavy flow days.
Period underwear vs. traditional products
When comparing period undies to traditional disposable period products, it’s hard to overstate the environmental and economic benefits.
Approximately 12 billion pads and 7 billion tampons are discarded each year in the U.S. alone, generating over 200,000 tons of waste. And plastic applicators can take decades to break down, often ending up in our oceans. The use of reusable period underwear not only cuts down on this harmful waste but can also save you money in the long run by eliminating or reducing your monthly spend on boxes of tampons and pads.
Relying on a reusable product can also ease some of the stress that comes with the menstrual cycle. As a period coach, Lisa Higgins’ work focuses on menstrual health awareness and inclusivity for individuals and organizations. She recommends period underwear to clients for economic and eco-friendly reasons, as well as to better connect with and work with their cycle.
“It's a revolution and so liberating to be able to bleed freely,” Higgins says as a user herself. “They're also so comfy, last way longer than tampons, and you don't need to worry about running out of tampons or pads.”
For some groups, period underwear may also be a safer option than other period products. Family, diversity, and lifestyle medicine physician Erkeda DeRouen, MD, notes that period underwear allows people who menstruate but don’t identify as women to navigate their cycle safely and comfortably, especially in environments with limited access to disposable products like men’s restrooms and prisons.
And in global cultures that shun women during menstruation, period underwear “may give them more opportunities to engage with society in an affordable, hygienic manner,” DeRouen says.
[Explore the differences between period underwear and pads to choose the right menstrual product for you.]
Is period underwear safe?
Period underwear may be revolutionizing menstrual care, but safety is still a key question. Recently, health-related concerns bubbled up around the presence of “forever chemicals” or polyfluoroalkyl substances (PFAS) in certain brands of period underwear.
Commonly used in clothing, food packaging, and countless other products, PFAS resist stains, oil, water, heat, and grease, which makes them popular in the manufacturing of consumer goods.
Despite this, experts have deemed period underwear safe to wear, as no evidence connects the PFAS in period underwear to any adverse health effects. Other experts have also noted that because PFAS are virtually inescapable in the products we use every day, period undies may be less of a concern, since they’re worn only a few days each month. Regardless, DeRouen notes that many brands are addressing consumer concerns and taking action to remove these harmful substances from their products.
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Fit and Quantity
Finding the pair that meets your needs may require some research and experimentation. Higgins recommends reading reviews to inform the decision, as folks often share insights based on their body type. The fit should feel secure but comfortable.
Many of them feel just like normal [underwear]. You forget you are on your period and they feel really slinky and even sexy.
Once you’ve made your choice, how many pairs should you buy? The answer can differ from person to person, but Higgins points out that many people assume they need to buy ten pairs all at once—a common misconception.
While having several pairs on hand from the get-go may seem smart, it’s better to purchase with intention. Start with a couple of pairs to gauge how they feel and fit into your cycle, she says.
While your typical flow level and cycle duration will factor into your decision, remember you’ll also be laundering between wears. The New Jersey Department of Health recommends changing and cleaning a pair of period underwear after 12 hours of use.
Care and washing
This brings up another common question: How should you wash period underwear? The same way you wash your regular underwear, but with some extra, super-simple steps.
Step 1: Rinse the period underwear in cold water till the water runs clear. Squeeze the gusset (i.e. the layers in the crotch area) to remove all the period blood trapped inside. Don’t soak the underwear, as this can weaken the layers over time, making the product less effective.
Step 2: Machine- or hand-wash it (whatever you prefer). If machine-washing it, use a cold, gentle cycle. In both cases, use a mild detergent that doesn’t contain any harmful chemicals.
Step 3: Air dry it. Don’t toss it into the dryer or wring it, unless the brand instructions say otherwise.
If you're worried about a period underwear smell after use, maintaining good laundering habits will not only keep them smelling fresh and clean but will also increase their longevity.
Explore LOLA’s reusable period underwear for different absorbency needs. [Shop now]
Making the transition to period underwear
Whether you’re fully free-bleeding or relying on period underwear for extra protection, the experience can take some getting used to. It’s helpful to have an idea of what to expect.
On heavier flow days, some users recommend pairing period panties with other products. But when it comes to lighter flow days, relying solely on period underwear has proven to be a safe bet. For example, Higgins opts for a menstrual cup for the first two to three days of her cycle before switching to period panties.
She also notes that, unlike regular underwear, one pair per day may not be enough. It’s possible you’ll need to change more often than the 12-hour laundering recommendation, depending on your flow.
“Don't be afraid to experiment, and don't worry if it takes a few goes to get it right,” she says. “Keep an open mind and see it as an adventure into something new.”
If you’re ready to begin a new chapter with your cycle through tampon alternatives, LOLA’s reusable period underwear provides the perfect place to start. One pair holds up to three tampons’ worth of liquid and comes in various sizes for a secure and comfortable fit.
FAQs
How does period underwear work?
Period underwear is typically made with three different layers of absorbent material over the gusset. It works by wicking the menstrual blood away from your skin and storing it within its layers. The final layer locks the fluid in, preventing it from escaping.
Does period underwear really absorb blood?
Yes, period underwear really does absorb blood—whether you have a light flow or a really heavy flow. Period undies designed for heavy flows can absorb up to 50 ml, or up to 7 tampons’ worth of blood.
Can you sleep in your period underwear?
Yes, you can sleep in your period underwear without having to worry about leaks since the absorbent layers run from the gusset all the way to the back of the undies. So, no matter which position you prefer to sleep in, your period undies will have your back.
How often should you change period underwear?
You should change your period underwear depending on your flow and comfort level, but, as a rule of thumb, they shouldn't be worn for more than 8-12 hours at a time.
Does period underwear smell?
Most period underwear is made of antimicrobial materials to prevent odors. Washing and drying them thoroughly will keep them from smelling funky.
Can teens use period underwear?
Yes, every menstruating person can wear period underwear, including teens.