'Stinkfluencers': Will following the skipping showers trend make you more attractive?

Across parts of the internet where young men trade tips on self-improvement, the latest project is scent.

Deodorant is out and washing less is in.

These "stinkfluencers" promise that the right aroma will work wonders on attracting a mate.

But while humans can find smells pleasant, or malodorous, or something in between, there's no evidence we can detect and respond to pheromones, let alone produce one.

Many animals communicate with pheromones, often around sex or marking territory. The problem is what happens when you look for the same sensory hardware in humans.

What is a pheromone?

A pheromone is a chemical messenger made inside the body of one member of a species, such as a cat, that's secreted or excreted and reliably produces a response in another member of that same species.

It's like openly broadcasting a chemical signal that is then picked up and acted upon by someone else.

Pheromones were first identified in silk moths back in 1959. That chemical, bombykol, is a sex-attractant released by female silkmoth to draw in mates.

A male silkmoth exposed to this pheromone will beat his wings and walk upwind toward the source. He doesn't have a choice in the matter and his response is inbuilt, not learnt.

Other animals, such as mice, pigs and cats, release and can sense pheromones. The purpose is usually to attract a mate or mark territory.

Not all animal pheromones have a fragrance

A pheromone isn't defined by whether you can smell it or by which organ picks it up.

Some pheromones are volatile and smellable. Bombykol, for example, is detected by ordinary smell (olfactory) receptors on the moth's antennae.

Others aren't detectable to us at all, such as the diffusers people plug in to chill out their cats.

What makes a chemical a pheromone is the reliability of the response it produces in members of the same species. Not whether it has a fragrance.

Humans don't have the anatomy to receive the message

For a pheromone to be functional, something has to be able to receive it.

In many four-legged animals, that job falls to the vomeronasal organ, a small structure in the nasal cavity. It's wired to a dedicated processing station in the brain called the accessory olfactory bulb.

But it doesn't have to be a dedicated organ. Plenty of pheromones are picked up by the ordinary smelling infrastructure — the lining of the nose in mammals, or, in the case of the silk moth, receptors on the antennae.

Some humans have a vomeronasal pit. But from birth, there are no nerve cells in it connecting to the brain, and no accessory olfactory bulb for a signal to report to.

What's more, no chemical has ever been found in humans that meets the criteria to be labelled a pheromone.

Can't sweat do something similar?

So if the signal isn't there and we couldn't receive it anyway, could the answer be in our sweat?

Not likely.

For a start, fresh sweat is practically odourless. Sweat is just a mix of 99 per cent water, electrolytes (salts) and then tiny amounts of urea, ammonia and other compounds.

If you stay sweaty and avoid washing yourself, eventually that sweat will provide a cosy breeding ground for bacteria, and that will start to cause a stench. It's unlikely to be an attractive odour.

But people can find smells attractive, of course. Though this is more likely to be due to positive associations, such as fancying someone or being romantically involved with them.

What about the T-shirt study?

In a 1995 study that gets a lot of play in the pop-psych and maxxing communities, male students wore a T-shirt for two consecutive nights after not washing with soap or using deodorants or other fragrant products.

Female students sniffed and rated six T-shirts each.

Both groups of students had also given samples for gene testing. Each woman was given three shirts worn by men whose major histocompatibility complex (MHC) genes (the ones her immune system uses to recognise invaders) were similar to her own, and three worn by men whose MHC genes were different.

The main result implied women preferred the smell of T-shirts worn by men with different MHC genes. But, among women taking the contraceptive pill, the preference switched. They rated men with similar genes as smelling better.

The interpretation was that women could sniff out men who are "immune-system compatible." In other words, people with more variety in their MHC genes have more tools to fight off infection. So being attracted to mates whose MHC genes are different from yours means any resulting children will have stronger immune systems.

The idea didn't come out of nowhere. Mate choice is influenced by scent in many other vertebrate species, and MHC has a role.

But the study doesn't hold up well

Despite how the T-shirt study caught the public imagination, there are two problems for pheromone maxxing.

First, the results don't hold up all that well. A 2020 meta-analysis of all the studies that tested for MHC-odour effects in humans found no overall effect.

It also found evidence of publication bias. That happens when people get more excited about publishing their positive results, and when journals prefer the eye-catching stories.

We suggest that showering with soap and using deodorant is still the best route to maxxing olfaction-attraction.

Samuel Cornell is a research fellow in public health at The University of Queensland.

He does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

Rob Brooks is a scientia professor of evolution at the University of New South Wales.

He receives funding from the Australian Research Council.

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