Menstrual cups are generally considered safe, but they come with real drawbacks that don’t get enough attention. The suction mechanism that keeps them in place can interfere with IUDs, the enclosed design can promote bacterial growth, and improper removal techniques may stress the pelvic floor. Here’s what the evidence actually shows.
IUD Expulsion Risk Is Significant
If you use an IUD for birth control, menstrual cups pose a serious compatibility problem. In a large prospective trial published in Obstetrics & Gynecology, copper IUD expulsion rates among menstrual cup users were 17.3% over two years, compared to just 5.2% among women using other menstrual products. That’s roughly a 3.8 times higher risk of your IUD being dislodged.
The problem gets worse over time. At year one, the expulsion rate for cup users was already 14.3% versus 4.7% for non-users. By year two, it climbed to 23.2% versus 6.5%. Nearly a third of the expulsions in cup users happened during cup removal, when breaking the suction seal can tug on IUD strings or shift the device. This isn’t a theoretical concern. It’s a measurable, replicated finding that means roughly one in five cup-and-IUD users will lose their contraceptive protection within two years.
Cups Can Promote Toxic Shock Syndrome Bacteria
Menstrual cups are often marketed as safer than tampons when it comes to toxic shock syndrome (TSS), but lab research tells a more complicated story. A study in Applied and Environmental Microbiology found that the bacteria responsible for TSS actually grew to higher levels in menstrual cups than in tampons. The reason: cups introduce more air into the vaginal canal, and the bacteria that produce TSS toxin thrive in oxygen-rich environments.
Larger cups produced more toxin than smaller ones, and silicone cups supported more bacterial growth than those made from thermoplastic elastomers. The researchers concluded that aeration from the cup’s shape and volume influenced toxin production more than the material itself. At least one confirmed case of menstrual TSS linked to a silicone cup has been documented in the Canadian Journal of Infectious Diseases and Medical Microbiology. While TSS remains rare with any menstrual product, the idea that cups eliminate the risk is wrong.
Pelvic Floor Strain From Removal
Many menstrual cup brands instruct users to “bear down” with their pelvic floor muscles to push the cup low enough to reach with their fingers. Physiotherapists have raised alarms about this advice. Kate Lough, a pelvic health physiotherapist, told the BBC that bearing down on the cup directly counters the guidance women receive to prevent pelvic organ prolapse. Repeatedly pushing downward weakens the muscles and connective tissue that hold pelvic organs in place.
At least one woman has been diagnosed with a minor vaginal prolapse attributed to three months of cup use, confirmed by a gynaecologist. While large-scale studies on this specific risk are limited, the mechanical logic is straightforward: if you’re straining to push something out of your vagina multiple times a month for years, you’re training your pelvic floor in exactly the wrong direction. Women who already have pelvic floor weakness, have given birth recently, or are prone to prolapse face higher risk.
Urinary Problems From Poor Fit
The vagina sits right next to the urethra and the tubes that drain the kidneys. A menstrual cup that’s too large or poorly positioned can press against these structures and partially block urine flow. The BMJ reported on cases where women developed kidney-related symptoms from cup pressure on the ureter, the tube connecting the kidney to the bladder. In one case, symptoms cleared completely once the woman stopped using the cup, confirming it as the cause.
Some women notice they have difficulty urinating or feel increased urgency while wearing a cup. Firmer cups are more likely to cause this pressure. In the reported cases, women who switched to a smaller cup and repositioned it more carefully were able to resume use without symptoms, but the fact remains that getting the wrong size can quietly interfere with your urinary tract in ways you might not immediately connect to your menstrual product.
Hygiene Is Harder Than It Looks
Menstrual cups need to be removed, emptied, rinsed, and reinserted every 8 to 12 hours. At home, this is manageable. In a public restroom with a shared sink outside the stall, it becomes a genuine logistical problem. You’re handling a blood-filled silicone cup with no running water within arm’s reach, trying not to spill on the seat, the floor, or your clothes, and then reinserting a product you can’t properly rinse.
Experienced cup users describe carrying spray bottles of soap, packs of baby wipes, and pre-dampened paper towels to manage public bathroom changes. Some have learned through messy trial and error that toilet paper disintegrates when wet enough to clean blood, that warm water stains the cup, and that removing the cup while standing is a recipe for spills. None of this is dangerous on its own, but it’s a real daily barrier that cup advocates tend to downplay. For people who work long shifts, travel frequently, or share bathrooms with limited privacy, the maintenance demands can be genuinely impractical.
Allergic Reactions Are Rare but Real
Most menstrual cups are made from medical-grade silicone, which the FDA considers biocompatible. True silicone allergies are rare, and no published studies have directly linked silicone allergy to menstrual cup use. But adverse event reports filed with the FDA describe symptoms including vaginal swelling, pain during movement, pain with temperature changes, and pain during intercourse. In at least one case, symptoms persisted after cup removal and were severe enough to interfere with daily life.
It’s worth noting that some cups contain dyes, and cheaper cups sold online may not use certified medical-grade materials. If you experience irritation, swelling, or unusual pain that starts after beginning cup use and resolves after stopping, the cup is the likely culprit, whether from the silicone itself or from additives in lower-quality products.
Cups Do Have Genuine Advantages
For balance, it’s worth noting that the same body of research shows clear benefits. A randomized study involving adolescent girls in Kenya found that cup users had a 35% lower prevalence of bacterial vaginosis and a 52% reduction in sexually transmitted infections compared to girls using other products. A large Lancet review of 43 studies involving 3,300 women concluded that menstrual cups are a “safe option” overall. They produce less waste, cost less over time, and don’t contain the bleaches or fragrances found in some disposable products.
The drawbacks are real, but they’re mostly situational. If you have an IUD, the expulsion risk is a dealbreaker worth taking seriously. If you have pelvic floor concerns, the removal technique matters more than the product itself. And if you’re considering switching, sizing and fit aren’t just comfort issues; they affect whether the cup presses on surrounding anatomy in ways that cause problems you wouldn’t expect from a menstrual product.