What Is a Menstrual Cup and How Does It Work?

A menstrual cup is a small, flexible, bell-shaped device worn inside the vagina during menstruation to collect blood rather than absorb it. Made of medical-grade silicone or thermoplastic elastomer, the cup sits low in the vaginal canal, forms a light seal against the vaginal walls, and holds fluid until you remove it, empty it, rinse it, and reinsert it. Most cups can be reused for years, which sets them apart from disposable tampons and pads in ways that go beyond convenience. The science behind their safety, their surprising effects on vaginal health, and the practical quirks of using one are all more interesting than a product description might suggest.

How a Menstrual Cup Actually Works

You fold the cup into a narrow shape, insert it into the vaginal canal, and let it spring open. Once open, the rim presses gently against the vaginal walls, creating a low-pressure seal that prevents blood from leaking past. Menstrual fluid pools inside the cup’s basin. When you’re ready to empty it, you pinch the base to release the seal, pull the cup out, pour the contents into a toilet or sink, rinse the cup with water, and reinsert it. Between cycles, most manufacturers recommend sterilizing the cup in boiling water for a few minutes.

The key difference from a tampon is that a cup collects rather than absorbs. A tampon works like a sponge, drawing fluid into its fibers. A cup simply catches it. This distinction matters for vaginal dryness: because cups don’t pull moisture from the vaginal walls the way absorbent products can, many users report less irritation. It also matters for how long you can wear one. Most cups can safely stay in place for up to twelve hours before needing to be emptied, compared with the four-to-eight-hour recommendation for tampons.

What They’re Made Of and Why It Matters

The vast majority of menstrual cups are made of medical-grade silicone, a material chosen for its flexibility, durability, and biological inertness. A smaller number use thermoplastic elastomer (TPE) or, less commonly, natural rubber latex. A safety assessment of a medical-grade silicone cup found no toxicological concerns when the material was tested under conditions mimicking vaginal use, including extraction at body temperature for 72 hours and under accelerated high-temperature conditions. No new chemical entities appeared in either test scenario, and the compounds detected above trace thresholds in the raw silicone were equal to or lower in the finished cup, with the only exception being harmless solvent salt clusters irrelevant from a safety standpoint.¹

That said, menstrual cups aren’t regulated as tightly as you might expect. In most countries, they’re classified as general wellness devices rather than medical devices, which means they don’t go through the same premarket review process as, say, an IUD. Quality can vary. The practical takeaway: choose a cup from a manufacturer that specifies medical-grade silicone or TPE and check for regulatory clearance in your country if it’s available.

Size, Stiffness, and Why Not All Cups Feel the Same

Walk into a drugstore or browse online and you’ll find cups marketed as “small” and “large,” typically with the smaller size aimed at people under 30 or those who haven’t given birth vaginally. But those labels hide enormous variation. A comparison study of cups all marketed to the same demographic (under-30, no prior vaginal birth) found that total volume ranged from roughly 19 mL to 38 mL, and the force needed to compress a cup to half its diameter ranged from about 3.4 newtons to nearly 14 newtons.² That’s a fourfold difference in stiffness between the softest and firmest cups supposedly designed for the same person.

Stiffness affects comfort, ease of insertion, and how reliably the cup pops open to form a seal. A very soft cup might fold easily but struggle to unfold inside the vaginal canal, leading to leaks. A very firm cup opens reliably but can press uncomfortably against the bladder or vaginal walls. Volume matters too: if your flow is light, a large-capacity cup may be unnecessary and harder to position comfortably. If your flow is heavy, a small cup might need emptying more frequently than you’d like. There’s no universal “best” cup. Finding the right one often takes experimenting with one or two brands.

Capacity and Leakage Compared to Tampons and Pads

One common selling point for menstrual cups is that they hold more blood than tampons. The reality is more nuanced. A study measuring the red blood cell capacity of modern menstrual products found that tampons, heavy or ultra pads, and menstrual cups held broadly similar amounts of blood, in the range of roughly 20 to 50 mL depending on the specific product.³ The overlap is wider than the marketing suggests.

As for leakage, a systematic review that pooled data from studies directly comparing cups with tampons or pads found that leakage was similar in most studies, with one study showing significantly less leakage among cup users.⁴ The same review noted that cups have been successfully used by people with heavy periods, since even a moderately sized cup can hold a meaningful volume when positioned correctly. The bottom line: a cup won’t necessarily hold dramatically more than a super tampon, but it won’t leak more, either, and it gives you a longer window before you need to deal with it.

The Learning Curve Is Real

If you’ve tried a menstrual cup once, found it awkward, and shoved it to the back of a drawer, you’re not alone. Virtually every study that tracks cup adoption finds a familiarization phase that lasts several menstrual cycles. A large systematic review reported a learning curve of two to five months in studies conducted in low- and middle-income countries, and longitudinal data from Kenyan schoolgirls showed that self-reported cup use rose from 84% in the first three months to 96% after nine months.⁵ Objective measures backed this up: physical signs of cup use (color change in the silicone) took a median of five months to appear across participants.⁵

Peer support makes a meaningful difference. In a Nepalese study, participants who reported increased cup use at two months were more likely to have friends who had also successfully used the cup. Once users get through the learning period, most stick with it: across 15 studies, about 73% of participants said they were willing to continue using the cup after the study ended.⁶ The practical advice here is simple: give yourself at least three full cycles before deciding a cup isn’t for you, and consider wearing a liner as backup while you’re learning.

Effects on Vaginal Health

This is where the evidence gets genuinely surprising. You might expect that inserting a foreign object for hours at a time would increase the risk of vaginal infections. The data suggest the opposite. A systematic review and meta-analysis combining results from five studies across three continents found that cup users had about a 21% lower rate of bacterial vaginosis (BV) compared to non-users.⁷ Cup users were also more likely to have an optimal vaginal microbiome composition dominated by beneficial Lactobacillus species.⁷

A randomized controlled trial in Kenyan schools reinforced these findings. Compared to the control group, participants assigned to the menstrual cup arm had 26% lower odds of BV and 37% increased odds of having that optimal Lactobacillus-dominant microbiome profile.⁸ Across all the infections evaluated in the meta-analysis, no increased risks were found among cup users.⁷

The leading explanation is that cups, unlike absorbent products, don’t strip the vaginal environment of its natural moisture and microbial defenses. Tampons absorb not just blood but also vaginal fluid that contains protective bacteria. A cup collects blood without disturbing the surrounding ecosystem.

Toxic Shock Syndrome and Cups

Toxic shock syndrome (TSS) is the fear that follows every internal menstrual product, and menstrual cups are not immune. The first documented case of TSS linked to a cup involved a 37-year-old woman using a menstrual cup for the first time.⁹ Additional case reports have followed.¹⁰ TSS from cups is rare, but it does happen.

An in vitro study added a wrinkle: under lab conditions mimicking typical use, menstrual cups produced higher levels of the toxin-producing Staphylococcus aureus growth than tampons did. The researchers attributed this to the additional air that cups introduce into the vaginal space, since the bacteria responsible for TSS thrive in the presence of oxygen.¹¹ This doesn’t mean cups are more dangerous than tampons in real-world use. TSS requires a specific combination of bacterial colonization, toxin production, and lack of immunity, which is uncommon regardless of the product. But it does mean that the standard hygiene advice applies to cups just as it does to tampons: wash your hands before insertion, empty the cup at recommended intervals, and sterilize between cycles.

Using a Cup with an IUD

If you have an intrauterine device (IUD) and are considering a menstrual cup, this section deserves your attention. Several lines of evidence point to an increased risk of IUD expulsion when the two are used together. A case series documented seven instances of IUD expulsion during concurrent menstrual cup use.¹² A secondary analysis from a large copper IUD trial provided harder numbers: through 12 months, about 16% of cup users experienced IUD expulsion versus 5% of non-users. By 36 months, the gap widened to roughly 23% versus 9%.¹³

Two mechanisms likely contribute. The suction created when you remove a cup can tug on IUD strings or shift the device downward. Separately, the strings can get mechanically caught during cup removal, causing what amounts to an accidental self-removal.¹⁴ In the copper IUD trial, accidental self-removal was substantially more common among cup users regardless of IUD type.¹³

If you want to use both a cup and an IUD, it’s worth discussing with your provider. Having your IUD strings trimmed shorter can reduce the chance of mechanical snagging, and being careful to break the seal before pulling the cup out (rather than yanking it straight down) may reduce suction-related expulsion. But the elevated risk is real and worth weighing, especially if replacing an expelled IUD would be costly or inconvenient.

Rare Urinary and Pelvic Floor Complications

A handful of case reports describe temporary urinary problems linked to cup use. A systematic review found three reported cases of hydronephrosis (swelling of the kidney due to urine backup) and one case of urinary incontinence, all of which resolved after the cup was removed.⁶ One case report described acute urinary retention, where the cup appeared to compress the urethra or bladder neck, made worse by a concurrent urinary tract infection. Symptoms resolved once the cup was taken out.¹⁵

A scoping review of pelvic floor outcomes associated with cup use found that the evidence was scattered and insufficient to establish that cups cause clinically meaningful pelvic floor dysfunction.¹⁶ The structural complications that have been reported are isolated cases and were reversible. If you notice difficulty urinating, pelvic pressure, or unusual discomfort while wearing a cup, remove it and try a softer or smaller size. These symptoms are a sign the cup is pressing on adjacent structures, not a sign that cups in general are unsafe.

Environmental and Economic Advantages

A single person who menstruates can use thousands of disposable pads or tampons over a lifetime. A reusable cup, which typically costs between $20 and $40 and lasts several years, replaces most of that waste. Life cycle assessments have consistently found that disposable tampons and pads carry far greater environmental impacts than a reusable cup across every category studied, including carbon emissions, water use, and landfill contribution.¹⁷ A comparative analysis across multiple countries confirmed that menstrual cups scored lowest across all environmental impact categories, with the most significant impacts coming from the initial production of the silicone and packaging rather than ongoing use.¹⁸

The economic argument is especially meaningful in settings where menstrual products are expensive or hard to access. In rural Ghana, a menstrual cup intervention achieved a 97% acceptability rate and significantly reduced reliance on unhygienic alternatives like old cloths and rags. Some participants adopted the cup as a replacement for disposable pads they couldn’t consistently afford, while others used the cup alongside pads on different days, citing the economic advantage of not needing to purchase pads as often.¹⁹ In contexts where missing school because of a lack of menstrual products is common, a one-time cup distribution can provide years of coverage.

Cups and Menstrual Poverty

Menstrual poverty, the inability to afford or access menstrual products, affects hundreds of millions of people worldwide and has cascading effects on school attendance, work participation, and dignity. Cups are increasingly being studied and distributed as an intervention because their reusability addresses the core economic barrier. Unlike a monthly pad supply chain that depends on ongoing funding, a cup distributed once can serve a user for years with only access to clean water for rinsing.

The Ghana intervention illustrates how this plays out on the ground. The cup didn’t just replace disposable products; it changed behavior in layered ways. Some girls switched entirely from rags to the cup. Others used the cup on heavier days and pads on lighter days, stretching their pad budget further. The complementary use pattern is worth noting because it reflects how real people adopt new products: rarely all-or-nothing, more often as part of a patchwork that adapts to their circumstances.¹⁹ A remaining challenge is that cup distribution programs need to include education and peer support. The learning curve documented across multiple studies means that handing someone a cup without guidance often leads to abandonment. Programs that pair distribution with hands-on instruction and community mentors see much higher sustained adoption, consistent with the broader finding that peer support improves uptake regardless of geographic setting.⁶

1
PubMed Central. Safety assessment scheme for menstrual cups and application for the evaluation of a menstrual cup comprised of medical grade silicone
2
SAGE Journals (Women’s Health). Comparison between menstrual cups: first step to categorization and improved safety
3
BMJ Sexual & Reproductive Health. Red blood cell capacity of modern menstrual products: considerations for assessing heavy menstrual bleeding
4
PubMed Central. Menstrual cup use, leakage, acceptability, safety, and availability: a systematic review and meta-analysis
5
PubMed Central. Use of menstrual cups among school girls: longitudinal observations nested in a randomised controlled feasibility study in rural western Kenya
6
The Lancet Public Health. Menstrual cup use, leakage, acceptability, safety, and availability: a systematic review and meta-analysis
7
PubMed Central. Effect of menstrual cups on vaginal health, reproductive tract and urogenital infections: a systematic review and meta-analysis
8
PLOS Medicine. Analysis of bacterial vaginosis, the vaginal microbiome, and sexually transmitted infections following the provision of menstrual cups in Kenyan schools: Results of a nested study within a cluster randomized controlled trial
9
PubMed Central. A confirmed case of toxic shock syndrome associated with the use of a menstrual cup
10
PubMed Central. Menstrual Cup-Associated Toxic Shock Syndrome
11
PubMed Central. Toxic shock syndrome associated with menstrual cup use
12
PubMed. Unintentional IUD expulsion with concomitant menstrual cup use: a case series
13
PubMed Central. Menstrual cup use and intrauterine device expulsion in a copper intrauterine device randomized trial
14
PubMed Central. Menstrual cup and risk of IUD expulsion – a systematic review
15
Acta Urológica Portuguesa. Acute Urinary Retention and Menstrual Cup Use: Case Report
16
SpringerLink. Pelvic Floor-Related and Genitourinary Outcomes Associated with Menstrual Cup Use: A Scoping Review
17
Resources, Conservation and Recycling. The value of reusable feminine hygiene products evaluated by comparative environmental life cycle assessment
18
Cleaner Environmental Systems. Menstrual products: A comparable Life Cycle Assessment
19
British Journal of Healthcare and Medical Research. Innovations in Addressing Menstrual Poverty in Africa: The Menstrual Cup Intervention for Girls in Rural Ghana