Menstrual cups are increasingly promoted as reusable, cost-effective alternatives to disposable period products, but a new study reveals important details about bacterial growth on cups during real-world use. Researchers at multiple institutions tracked 172 adolescent girls in western Kenya over 30 months, collecting 369 menstrual cup samples to understand what bacteria live on cup surfaces and how cup hygiene affects vaginal health.

What Bacteria Actually Live on Menstrual Cups?

The research found that menstrual cup surfaces primarily hosted soil and water bacteria, which is unsurprising given the environmental conditions in low-resource settings where access to clean water is limited. However, the study also detected bacteria typically found in the vagina itself, including Lactobacillus crispatus, Lactobacillus iners, and Gardnerella vaginalis. This suggests that cups can pick up vaginal microbes during use and storage, which is a normal part of how the product functions.

More concerning were findings about potential pathogens. Escherichia coli (E. coli) was detected on 36% of cups sampled, though at low levels averaging just 0.09% of the total bacteria present. Staphylococcus aureus appeared on 24% of cups, with a mean relative abundance of 0.36%. While these percentages sound small, understanding their presence matters for users in settings where water quality and sanitation infrastructure are compromised.

Which Factors Increase Pathogenic Bacteria on Cups?

The study identified specific conditions that raised the risk of harmful bacteria accumulating on menstrual cups. Damaged cups showed significantly higher levels of E. coli and S. aureus compared to intact cups, suggesting that wear and tear creates crevices where bacteria can lodge and multiply. Additionally, participants with certain vaginal health conditions, including HSV-2 (herpes simplex virus type 2) infection or non-optimal vaginal microbiome patterns, had higher pathogenic bacteria on their cups.

Interestingly, antibiotic use was associated with lower E. coli presence on cups, likely because antibiotics reduced the bacteria in the vagina itself, which is a primary source of cup contamination. Age also mattered: older participants in the study had lower contributions of vaginal bacteria to their cup microbiota, possibly reflecting more established cleaning and storage habits.

How to Maintain Menstrual Cup Safety and Hygiene

• Access to Clean Water: The most critical factor for safe cup use is reliable access to clean water for rinsing and cleaning between uses. In settings where water quality is poor or water is scarce, the risk of pathogenic bacteria accumulation increases significantly.
• Proper Cleaning and Storage Methods: Developing and following consistent cleaning protocols is essential. The study emphasizes that real-world cleaning practices vary widely by context, and interventions should focus on teaching effective methods suited to local conditions.
• Regular Cup Inspection: Users should regularly inspect their cups for signs of damage, cracks, or discoloration. Damaged cups should be replaced to prevent bacterial colonization in compromised areas of the silicone material.
• Sanitation Infrastructure: Communities need improved access to sanitation facilities, including clean water sources and appropriate spaces for menstrual hygiene management, to support safe cup use.

The research team noted that interventions should be tailored to local contexts. "Interventions focused on improved cleaning and storage tools and methods, and access to clean water and sanitation infrastructure are required to maximize safety of menstrual cup use in low-resource settings," the researchers stated.

Is the Menstrual Cup Still Safe to Use?

Despite the bacterial findings, the study reported no serious adverse events related to menstrual cup use among the 172 participants over the 30-month follow-up period. This is an important reassurance: the presence of bacteria on cup surfaces does not automatically translate to infection or health problems, especially when cups are used with reasonable hygiene practices.

In fact, previous research cited in the study suggests menstrual cups may offer protective health benefits. Studies have found that cup users had a 37% increased likelihood of maintaining a healthy, Lactobacillus-dominated vaginal microbiome compared to pad users, and experienced 24% lower rates of bacterial vaginosis. Another study documented a 35% reduction in bacterial vaginosis among primary school students using cups compared to those using pads or no menstrual product. Additionally, a large randomized trial of over 4,100 adolescent girls found a 33% lower incidence of HSV-2 among cup users relative to controls.

The key takeaway is that menstrual cups remain a viable, long-lasting menstrual hygiene option with a strong safety profile, but their safety depends heavily on context. In settings with reliable access to clean water and sanitation, cups present minimal risk and significant environmental and economic benefits. In low-resource settings, targeted interventions to improve water access, sanitation infrastructure, and user education about cleaning and storage are essential to maximize safety and realize the cups' potential as a multipurpose tool for menstrual and reproductive health.