What exactly is that fishy smell?

We have such an association with vaginas and their fishiness that we often forget to ask why this fishy smell develops in bacterial vaginosis. It’s actually interesting! And it is, in fact, the same process found in rotting fish, but also found in some infections, bad breath, and BV odour.

The fishy odour is caused by a chemical reaction between molecules: ammonia (produced by G. vaginalis) and methanol react, with the help of a catalyst, and become trimethylamine (TMA).

FUN FISHY FACT: Fish – the ocean-dwelling kind – freshness tests are looking specifically for TMA. This is why we are told that if a fish ‘smells fishy’ (read: has a lot of TMA) then it’s not very fresh. This is because the TMA has had time to develop, indicating a longer time out of the water.

TMA is a product of decomposition in plants and animals, and in humans is mostly synthesised – put together – by gut microbes from nutrients in our food, specifically choline and carnitine. You can bring on this fishy smell by taking large doses of choline and carnitine, but foods that contain high levels of choline are eggs, milk, liver, red meat, poultry, shellfish and fish, and carnitine can be found mostly in red meat and dairy products.

You can’t avoid these nutrients, and nor should you – unless you have fishy odour syndrome or a metabolism disorder (explained below), you are not at any risk of this causing your fishy vagina.

Fishy odour syndrome

Fish odour syndrome is also known as trimethylaminuria, and is a rare genetic metabolic disorder that halts the production of an enzyme that stops the body being able to properly convert TMA into TMAO (trimethylamine oxide). TMA then builds up, and is excreted in sweat, urine, and the breath, causing the strong fishy odour in the breath and body.

The other way the excess excretion can occur is through excessive TMA being secreted, which could be due to gut microbiota issues, altered metabolism, or due to a hormone issue.

How TMA reacts with our noses – why we hate it

TMA is also an olfactory receptor agonist, which in plain English means when we breathe in TMA and it hits our nostrils, we hate it because our noses have been trained, over time, to be receptive to this compound. It causes an ‘attraction-aversion’ response, and that means it is triggering off a neurological reaction: our brain fires when we breathe in these amines, which doesn’t always happen with every odour we smell.

We are especially sensitive to some odours (molecules) over others, and this appears to be evolutionary: we are repelled by or attracted to certain molecules – delicious food over rotten food, for example.

TMA’s characteristic fishy odour is always an odour of decomposition in plant or animal, and therefore we are primed to reject it outright. It repels us. This is one reason why having a fishy vag is bad for life – it repels other people, because our animal brains are saying “Don’t eat this – it’s dangerous!” or “Don’t have sex with her! You don’t like her smell”. It is the same process by which pheromones are believed to operate.

An interesting way to block a lover’s nose from TMA… Timberol

A perfuming product called Timberol apparently blocks the TAAR5 receptors in our nose that TMA triggers, about 96 per cent of the time. This is pretty good going, and means you could put a bit of woody perfume on and it would block the fishy odour, except Timerol is not available to consumers – it’s a perfume developed for shampoo, shower gel, deodorants, and cleaning products. Timberol was developed by a company called Symrise.

Symrise says about Timberol: ‘powerful modifier for woody accords; imparts a substantive woody-ambery characteristic; strengthens the floral side in feminine concepts at low use levels; underlines the masculinity of men’s fragrances at high use levels.’ 

It’s a shame we can’t use it, though I’m sure if you were into it, you could get your hands on some.

The Whiff Test

The whiff test that a doctor or scientist can do that kills bacteria and vaginal cells using potassium hydroxide (KOH), which when BV is present, has a fishy odour. In a yeast infection, this test is used to kill the cell and bacteria, and leave just the yeast to detect.


Jessica Lloyd - Naturopathic Practitioner, BHSc(N)

Jessica Lloyd - Naturopathic Practitioner, BHSc(N)

Jessica is a degree-qualified naturopath (BHSc) specialising in vulvovaginal health and disease, based in Melbourne, Australia.

Jessica is the owner and lead naturopath of My Vagina, and is a member of the:

  • International Society for the Study of Vulvovaginal Disease (ISSVD)
  • International Society for the Study of Women's Sexual Health (ISSWSH)
  • National Vulvodynia Association (NVA) Australia
  • New Zealand Vulvovaginal Society (ANZVS)
  • Australian Traditional Medicine Society (ATMS)
Read more about Jessica and My Vagina's origin story.
Jessica Lloyd - Naturopathic Practitioner, BHSc(N)

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