We have seen women assume their cup smells because there is something wrong with the product, or worse, something wrong with their body. Almost always, neither is true. Menstrual cup odour has specific, identifiable causes, and every one of them is preventable and reversible with correct cleaning technique. This article explains each cause and gives you the complete elimination approach.
Does Menstrual Cups Smell by Nature?
No. Medical-grade silicone is chemically inert and odourless. Ruby Cup's expert cup hygiene guide confirms that a menstrual cup made from medical-grade silicone has no foul smell of its own because this type of silicone is medically biocompatible, meaning it does not interact with its surroundings the way an absorbent pad or tampon might.
This is the first important distinction: any odour associated with your cup is not coming from the silicone itself. It is coming from residue that has built up on or inside the silicone because of incomplete cleaning, incorrect cleaning method, or a prolonged period between sterilization sessions.
What Causes Cup Odour: Every Source Explained
1. Hot water used for the first rinse
This is the most common and most overlooked cause of persistent cup odour. Menstrual blood contains proteins. When protein-containing fluid is rinsed in hot water, it undergoes partial cooking (denaturation) that causes the proteins to bind to the silicone surface. This protein adhesion is what eventually produces a lingering smell.
Luneale's cup care guide makes this the golden rule of cup cleaning: always rinse your cup with cold water first. Cold water removes blood without setting proteins into the silicone. Once you have cold-rinsed, warm water and soap can be used. Reversing this order, hot water first, is what makes odour difficult to remove.
2. Blood oxidising inside the cup
Blood oxidises when exposed to air. If the cup is worn for an extended period or if the seal is not completely airtight, small amounts of air inside the cup allow oxidation to begin. Oxidised blood has a distinctive metallic or musty smell. Luneale's research also identifies that this is more common when a large cup is worn during a light flow day, because the cup is 90% air and only 10% blood. The large air volume inside accelerates oxidation.
3. Skipping sterilization between cycles
Rinsing and washing during the cycle removes surface contamination. It does not eliminate all bacteria and microorganisms that accumulate over the course of a full period. At the end of each period, the cup must be sterilized by boiling before storage. Bacteria that survive on the cup during storage and are reintroduced next cycle progressively produce odour that becomes harder to eliminate with each cycle that the sterilization step is skipped.
4. Using the wrong soap
Scented soaps, antibacterial soaps, and oil-based cleaners leave residue on the silicone surface. This residue combines with menstrual fluid, body heat, and bacterial activity during the next cycle to produce a chemical or synthetic odour that is particularly difficult to eliminate because it is embedded in the cleaning agent residue itself. Always use mild, fragrance-free, oil-free soap specifically compatible with silicone.
5. Natural bacterial interaction
A mild tangy, cheesy, or sour smell that develops after extended cup use is not always a hygiene failure. The vaginal environment is dominated by Lactobacillus bacteria that produce lactic acid, which has a mild sour smell. As Ruby Cup explains, some users find that their cup develops a sour smell because it interacts with this beneficial vaginal flora. This is actually evidence of a healthy vaginal microbiome and does not indicate infection or poor hygiene. A full end-of-cycle boil resolves this smell.
6. Incomplete cleaning of the suction holes
The small holes around the cup's rim are the most commonly overlooked cleaning area. Residue accumulates in these holes and cannot be removed by surface washing alone. Blocked holes also prevent effective suction-breaking during removal and can affect how odour-producing bacteria accumulate inside the cup between uses.
How to Eliminate Existing Cup Odour
If your cup already has a noticeable odour, these methods resolve it.
Method 1: The boil with a natural deodoriser
Boil the cup in water with one of the following additions (use only one at a time, not combined):
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A splash of white vinegar
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The juice of half a lemon
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A tablespoon of baking soda
Boil for 5 to 10 minutes. The combination of boiling temperature and the mild acid or base in each of these natural additions dissolves odour-causing residue from the silicone surface. This method is confirmed effective by Luneale's cup care research. Rinse the cup thoroughly with clean water after this boil before using or storing.
Do this in the Collapsible Sterilizer Cup to keep the cup off the hot pot base and to avoid using kitchen cookware.
Method 2: Sunlight exposure
UV rays in sunlight are natural antimicrobials and mild bleaching agents. After washing the cup, place it in a clean area with direct sunlight exposure for 2 to 4 hours. Sunlight reduces bacteria and can lighten mild discolouration while eliminating surface odour. Do this in the morning or afternoon to avoid extreme midday heat that could degrade silicone over time if sustained. Peachlife Inc's cup care guide confirms sunlight as an effective natural deodoriser for silicone cups.
Method 3: Clean the suction holes properly
Fill the cup with water, place your palm completely flat over the opening, and squeeze firmly. The pressure forces water through the suction holes, clearing any blockage. Repeat 4 to 5 times. For persistent blockages, use a clean toothbrush kept specifically for cup maintenance to clean each hole individually. Once the holes are clear, the boil-deodoriser method is more effective because the solution can access the inside of the holes.
Complete Prevention Protocol
During your cycle:
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Cold rinse first, every single time
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Then warm water + mild fragrance-free soap
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Pay specific attention to the rim and suction holes
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Do not exceed 12 hours of wear before emptying
End of cycle:
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Sterilize by boiling for 3 to 5 minutes in the Collapsible Sterilizer Cup
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Allow to air dry completely on a clean surface
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Store in the breathable pouch provided, not in an airtight container
Storage between cycles:
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Never store while damp
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Keep in a cool, dry location away from direct heat
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Check the cup for any discolouration or structural changes at the start of each cycle
When Odour Signals Something Else
A strong fishy smell from the cup is different from the mild sour or metallic smells described above. A persistent fishy odour accompanied by unusual discharge, particularly grey or watery discharge, is the clinical sign of bacterial vaginosis (BV), not a cup cleaning issue. The cup picks up the smell of the vaginal environment. If BV is present, the cup will reflect it. BV requires medical treatment, after which correct cup cleaning prevents recurrence.
If the smell from a cleaned cup is strong, chemical, or burns the nose, this may indicate the cup material has been damaged by incorrect cleaning products (alcohol, bleach, harsh chemicals). A cup with silicone breakdown should be replaced.
Discolouration: Related to Smell But Separate
Many women notice their cup turns yellow or brown over time. Discolouration is separate from odour. It is the nature of clear and light-coloured silicone to take on some staining from prolonged contact with blood. Discolouration does not affect the cup's safety, effectiveness, or hygiene. It is purely cosmetic. A cup can be discoloured and still be perfectly clean and safe to use.
Lemon juice + sunlight is the most effective natural method for lightening staining. The lemon juice acts as a mild bleaching agent, and UV from sunlight assists the process. Apply lemon juice to the washed cup, place in sunlight for 2 to 4 hours, then rinse thoroughly and boil before next use.
Frequently Asked Questions
Why does my menstrual cup smell bad?
The most common causes are: rinsing in hot water before cold, skipping end-of-cycle sterilization, using scented or antibacterial soap, blocked suction holes, or blood oxidising inside the cup. All are preventable and reversible with correct cleaning.
Does cup odour mean infection?
Mild sour or metallic odour from the cup is almost always a hygiene issue, not an infection. A strong fishy odour may indicate bacterial vaginosis in the vaginal environment. If you also have unusual discharge, particularly grey or watery, see a doctor.
How often should I replace my cup if it develops odour?
A cup that responds to the boil-deodoriser method and is cleaned correctly thereafter does not need replacement for odour alone. Only replace the cup if the odour persists after multiple thorough cleaning cycles, if the silicone has become sticky or tacky, or if there are visible tears or structural damage.
Can I use tea tree oil or essential oils to deodorise my cup?
No. Essential oils, including tea tree oil, degrade silicone over time and are not safe for internal intimate products. They can cause contact irritation when reinserted. Use only the natural methods listed above.
At MomDaughts, we believe most cup problems have simple solutions. Confidence in every cycle.
