We have seen women who have been rinsing and washing their cup after every use but never boiling it between cycles. The cup looks clean. It smells okay. Nothing obviously bad has happened. So does sterilization actually matter? Yes, and this article explains precisely why.
The Difference Between Clean and Sterile
Washing a cup with soap and water after each removal during your period achieves sanitization: it reduces the number of bacteria and removes visible residue to a level that is safe for reuse during that cycle. This is sufficient for mid-cycle cleaning because you are reinserting the cup into the vaginal environment that already contains its own natural bacteria.
But after a full period, the cup has been in contact with menstrual blood, vaginal secretions, and the vaginal microbiome for 5 to 7 days. Even with correct soap-and-water cleaning between uses, microscopic amounts of biological material accumulate in the suction holes, at the junction between the stem and body, and in any micro-texture of the silicone surface. Bacteria embedded at this level cannot be removed by soap and water alone.
When you store a sanitized-but-not-sterilized cup for 3 to 4 weeks until your next period, these surviving bacteria have time to accumulate on the cup surface. When the cup is inserted next cycle, these bacteria are introduced to the vaginal environment in higher concentrations than they would otherwise be.
What Can Happen If Sterilization Is Consistently Skipped
Persistent or worsening odour
The most immediate and most commonly noticed consequence. Bacteria that survive on the cup between cycles continue to produce odour compounds during storage. By the third or fourth cycle without sterilization, most users notice a smell from the cup that does not resolve with washing during the current cycle.
Increased risk of recurring BV
Bacterial vaginosis (BV) occurs when the balance of the vaginal microbiome is disrupted and Gardnerella vaginalis and other anaerobic bacteria overgrow. Introducing a cup that carries a higher-than-normal bacterial load directly into the vaginal canal is a documented pathway to recurring BV in women who are prone to it. This is not the same as saying BV is guaranteed. It means that for women who already experience BV, skipping cup sterilization is a contributing risk factor.
Discolouration that becomes permanent
Biological residue embedded in the silicone from multiple cycles without sterilization causes discolouration that becomes increasingly difficult to reverse. Correct end-of-cycle sterilization, including boiling with a natural deodoriser, removes the accumulation before it embeds deeply. Without this, the cup surface yellows or browns progressively.
In rare cases, increased infection risk
The Lancet's systematic review of menstrual cup safety found that in the rare cases of TSS or infection associated with cup use, improper cleaning was a documented common factor. Skipping sterilization does not guarantee an infection, but it removes one of the key hygiene safeguards that makes cup use as safe as the clinical evidence shows it to be.
The Correct Sterilization Method
Boiling remains the simplest, most accessible, and most reliable sterilization method for medical-grade silicone cups.
Place your clean cup in the Collapsible Sterilizer Cup, fill with water to fully submerge the cup, and bring to a boil on the stovetop. Boil gently for 3 to 5 minutes. Alternatively, use the microwave method: fill the sterilizer, place the lid slightly open, and microwave on high for 2 to 3 minutes until the water reaches a full boil.
Allow to cool completely. Remove the cup, air dry fully, and store in the breathable pouch provided.
This step takes approximately 10 minutes and happens once per menstrual cycle. It is the single most important hygiene step in the entire cup care routine.
Is It Safe to Skip One Cycle?
Missing one end-of-cycle sterilization is not a crisis. Give the cup a thorough boil at the beginning of the next cycle before first use. This corrects the missed step before reintroduction.
Chronically skipping sterilization for multiple consecutive cycles is where the cumulative consequences described above develop. One missed boil is easily corrected. Six missed boils means six cycles worth of bacterial accumulation that is progressively harder to reverse.
What If the Cup Has Never Been Sterilized?
If you have been using a cup for several months or longer without ever sterilizing it, do the following.
Wash the cup thoroughly with mild soap. Then do an extended boil in water with a splash of white vinegar for 10 minutes. Allow to cool, rinse thoroughly, and inspect the cup for any discolouration, stickiness, or structural changes. If the cup looks and smells acceptable after this deep clean, resume correct care going forward, including end-of-cycle sterilization.
If persistent odour or significant discolouration remains after the deep clean, it may be time to replace the cup and start fresh with correct care from the beginning. Browse the full menstrual cups collection for all available variants.
Frequently Asked Questions
What happens if I forget to sterilize my cup?
For a single missed cycle, boil the cup before your next use. Consistently skipping sterilization over multiple cycles leads to progressive odour buildup, discolouration, and increased risk of introducing accumulated bacteria into the vaginal environment when the cup is reinserted.
Can I sterilize with boiling water poured over the cup instead of submerging it?
Pouring boiling water over the cup surface is not equivalent to boiling the cup in water. The sustained 100°C heat of submersion is what achieves sterilization. Surface pouring cools too quickly to sterilize effectively.
How do I know if my cup needs replacing rather than just better cleaning?
Replace the cup if persistent odour remains after multiple correct sterilization cycles, if the silicone has become sticky or tacky to the touch, if there are visible tears or chips, or if significant black or dark discolouration appears (surface yellowing does not require replacement).
At MomDaughts, we believe the small steps in cup care are what make the product safe and effective long-term. Confidence in every cycle.
