Common Causes (Ranked by Likelihood)
Menstrual blood is alkaline (pH ~7.4), which raises the normally acidic vaginal environment (pH 3.8-4.5). This pH shift allows anaerobic bacteria (Gardnerella, Prevotella, Mobiluncus) to multiply rapidly, producing trimethylamine and other amines that smell fishy or metallic. Many people with BV notice their worst symptoms during and immediately after their period. This isn't a hygiene issue — it's a chemical environment shift that promotes bacterial overgrowth.
Blood contains iron, and when iron in hemoglobin oxidizes on contact with air and skin bacteria, it produces a metallic, slightly musky smell. This is completely normal. The smell is more intense with heavier flow (more blood = more oxidation), after sitting for extended periods, and when using pads (which expose blood to air) versus tampons (which limit air exposure). The smell is not caused by poor hygiene — it's basic biochemistry.
A forgotten tampon or retained menstrual cup left too long will create a severely foul, rotting smell that is unmistakably different from normal period odor. This can also occur if a tampon became lodged higher in the vaginal canal. This is a medical concern — left untreated, it can cause infection and in rare cases, toxic shock syndrome.
Foods high in sulfur compounds (garlic, onions, cruciferous vegetables, red meat) affect body secretions including menstrual odor. Dehydration concentrates all bodily fluids, including vaginal secretions. Alcohol consumption around your period can also intensify body odors. These effects are temporary and harmless.
Trichomoniasis, chlamydia, or pelvic inflammatory disease (PID) can produce a foul, fishy, or musty odor that's more noticeable during menstruation. Trichomoniasis specifically produces a frothy, yellow-green discharge with a strong odor. Chlamydia and gonorrhea are often odorless but can cause secondary infections. If you have risk factors for STIs (new partners, unprotected sex), these should be ruled out.
How to Fix It
Manage BV Around Your Period
$5-50BV is highly treatable — the key is treating the infection rather than masking the smell.
- 1See a doctor for a swab test. BV is diagnosed in minutes and treated with a short course of metronidazole or clindamycin.
- 2OTC boric acid vaginal suppositories (600mg) can help restore acidic pH and are evidence-based for BV. Use in the week before your period if you get recurrent BV.
- 3Avoid douching — it raises vaginal pH and worsens BV.
- 4Consider vaginal Lactobacillus probiotics to help maintain a healthy microbiome between periods.
- 5After your period, the pH typically normalizes — BV may resolve on its own for mild cases, but persistent symptoms need treatment.
Reduce Normal Period Odor
$5-30For the normal metallic/musky smell that's just biology.
- 1Change pads every 3-4 hours to reduce oxidation time — most odor develops when blood sits on the pad and oxidizes.
- 2Consider switching to period underwear, which controls odor better than most pads.
- 3Wash the external vulva (not internally) with unscented, gentle soap during your period.
- 4Stay hydrated — diluted bodily fluids smell less intense.
- 5Menstrual cups reduce odor compared to pads because the blood doesn't contact air until you empty the cup.
Check for Forgotten Products
$0If the smell is dramatically worse than normal — check first.
- 1Gently check for a retained tampon yourself, or have a gynecologist do it — don't ignore a suddenly severe smell.
- 2If you find one, remove it gently. If you're unsure or it's difficult to reach, see a doctor.
- 3After removal, odor should resolve within 24-48 hours.
- 4If you have fever, pelvic pain, or feel unwell with a retained tampon — go to urgent care immediately (possible TSS risk).
- 5Consider menstrual cycle tracking apps to help you remember when you last changed your product.
When to Call a Professional
Rotting or very foul smell — rule out a retained tampon or other foreign object immediately.
Smell with fever, pelvic pain, or feeling unwell — possible pelvic inflammatory disease or toxic shock; seek emergency care.
Unusual discharge color (green, gray) alongside bad smell — possible STI or infection; get tested.
Odor getting progressively worse over multiple cycles — see a gynecologist for a proper diagnosis rather than self-treating.
Post-menopausal bleeding with odor — should always be evaluated by a doctor.
How to Prevent It
Change menstrual products frequently — every 3-4 hours for pads, 4-8 hours for tampons.
Consider menstrual cups or period underwear — many people find these produce less odor than disposable pads.
Never douche — raises vaginal pH and makes BV more likely.
Use unscented products — scented pads, tampons, and wipes can irritate and disrupt vaginal flora.
Stay hydrated during your period — diluted secretions smell less intense.
Wear breathable, cotton underwear during your period to allow airflow.
What's Actually in Period Blood?
Menstrual fluid is a mixture of blood (about 36%), cervical mucus, vaginal secretions, and shed endometrial tissue. The blood is arterial and venous, containing iron-rich hemoglobin. As hemoglobin breaks down and iron oxidizes, it produces the characteristic metallic smell. The darker, brownish blood at the end of a period is older blood that has had more time to oxidize — which is why it often has a stronger smell.
The vaginal bacteria present during menstruation also contribute significantly to odor. Lactobacillus bacteria (healthy) produce lactic acid with little odor. When the pH shift from blood promotes anaerobic bacteria (BV-associated), these produce amines that have a distinctive fishy smell. This is why two people can have very different period odors based on their vaginal microbiome.
Frequently Asked Questions
Not really — a fishy period smell usually indicates bacterial vaginosis (BV) that is flaring during your period due to the pH change. A mild metallic or musky smell is normal, but fishy is a sign the vaginal microbiome has shifted. BV is very common and easily treatable with antibiotics or boric acid.
Possible reasons: a BV flare (if fishy), a forgotten tampon (if rotting), a diet change, or hormonal shifts. If the smell is dramatically different from your normal and accompanied by unusual discharge or any pain, see a gynecologist.
Scented pads might briefly mask the odor, but they often cause more problems than they solve. The fragrance chemicals can irritate sensitive vulvar skin and disrupt the vaginal microbiome, which can actually increase bacterial odors long-term. Unscented pads changed frequently are more effective.
No — period odor varies significantly between individuals based on their vaginal microbiome, diet, hydration, the products they use, and the hormonal balance of their particular cycle. What's 'normal' for one person may be different for another. What matters is whether your period smell has changed noticeably for you.