Can neuroscents change the way we feel?

BY JASMIN FOX-SKELLY

Modern perfumes are promising a lot more than to merely make us smell good. New ‘neuroscents’ are claimed to alter our brain chemistry and change how we feel. But do they work? Jasmin Fox-Skelly reports.

The fragrance industry is big business, with annual sales of $70bn worldwide. To tap into this demand, perfumiers are now selling fragrances designed to trigger specific emotional responses. These ‘neuroscents’ can evoke feelings from calm and relaxation, to euphoria and happiness, it is claimed. The International Fragrance Foundation (IFF), for example, says it has tested thousands of fragrance notes over the years to find ingredients that trigger specific brain patterns linked to various emotional states. They have developed an AI algorithm called Scentcube to identify six emotions that can be targeted by the power of scent alone.

Meanwhile, scientists at Givaudan in Switzerland, one of the world’s biggest fragrance suppliers, say that they have used fMRI scans and electroencephalograms (EEGs) to map the electrical signals produced by the brain in response to perfume smells. Givaudan’s database of neuroscents, known as MoodScentz, covers three emotional states: invigorated, happy and relaxed. L’Oreal Paris has even partnered with neurotechnology company Emotiv to create an in-store EEG headset aiming to help shoppers find the new Yves Saint Laurent fragrance that’s the ‘right scent for them’. The company claims that 95% of customers who use the headset find the right perfume.

However, is this backed up by real science? There is certainly evidence that smells can evoke positive emotions and influence wellbeing. In a 2018 study, researchers showed that exposure to linalool, an alcohol found in lavender extracts, reduced the anxiety of mice placed in stressful test environments [1]. The scent’s effect was comparable to anti-anxiety drug diazepam. Meanwhile, numerous studies show aromatherapy can relieve stress in humans. In one, hospitalised patients awaiting haemodialysis were given a handkerchief infused with drops of rose water [2]. Inhaling the scent was shown to reduce anxiety levels. In a separate study, seventh-grade students awaiting a test sniffed a handkerchief containing oil from the tuberose, a flowering plant from the lily family [3]. The students reported the scent reduced their pre-test anxiety. 

There are hundreds of studies showing that certain smells, such as lavender, can promote relaxation. But what about other emotions? A 2019 study asked 100 people to either wear a peppermint-infused skin patch or a blank patch for six hours, during which time they went about their normal daily routine. The study showed that inhaling the scent of peppermint improved the memory, attention and feelings of ‘subjective alertness’ of people in the test group, compared with controls [4].

The ability of certain scents to make us feel happy may be intrinsically tied to its role in boosting memory. For example, a 2016 review of the clinical literature by Rachel Herz, a cognitive neuroscientist and one of the world’s leading authorities on the psychology of smell, concluded: ‘Odours that evoke positive autobiographical memories have the potential to increase positive emotions, decrease negative mood states, disrupt cravings, and reduce physiological indices of stress, including systemic markers of inflammation.’ [5]

‘We’ve all had this experience of smelling something, and it evokes some long-forgotten memory,’ says Stuart Firestein, an olfactory neuroscientist at Columbia University, US. ‘These memories that are evoked always have an emotional content. It’s always the first day of school, your grandmother’s house, your first lover, your last love, or something like that. You never smell something and remember a page of text or a phone number.’

There’s evidence that pleasant aromas can even boost ‘non-autobiographical’ memory. In one six-month study in 2023, Michael Leon, Professor Emeritus of neurobiology and behaviour at the University of California–Irvine, US, gave adults aged between 60 and 85 word recall tests, along with fMRI scans, to assess their cognitive function [6].

Half of the participants were then given a scent diffuser to plug in at night while they slept. The diffuser released seven different scents, one for every day of the week.

Amazingly, after six months, those who inhaled essential oils for a few hours each night showed a 226% improvement in cognitive performance measures like verbal learning and memory, compared with the control group. According to Leon, there are now about 20 studies showing that if you give pleasant odours to someone, you will improve their memory system. One study in South Korea even showed that olfactory enrichment could improve memory and attention in people with dementia. [7]

‘If a drug came out and showed the same dramatic improvements in dementia patients that olfactory enrichment does, it would be front page news,’ says Leon. ‘It is, in my opinion, the most effective treatment for dementia, and without any of the problems associated with the new drugs that have been developed, such as brain bleeds, brain inflammation, and brain shrinkage.’

However, the Alzheimer’s Society suggests such claims should be treated with caution. There is limited research in this area, and those studies that have been done have only tested a small number of people over short timescales. It is therefore difficult to extrapolate from those research findings the suggestion that olfactory enrichment would be the most effective treatment for dementia.

On the other hand, losing your sense of smell – a condition called anosmia – can be damaging to mental and physical health. For example, in areas where people are exposed to bad odours from industry or agriculture, rates of depression are much higher, even when poverty levels and socioeconomic status are accounted for.

‘I’ve identified 139 medical conditions associated with olfactory loss, including cardiac disease, schizophrenia, dementia, cancer, depression, multiple sclerosis,’ says Leon. [8] ‘So it shouldn’t be surprising that by middle age, your all-cause mortality – that is whether you die for any reason – can be predicted accurately by your olfactory ability.’ [9]

Smell circuits

But how can smelling a scent have such a powerful effect on wellbeing and memory? Relatively little is known about the mechanics of how we smell. We know the lining, or epithelium of the human nose is packed with olfactory neurons, each containing around 450 different types of smell receptors, that together can process a trillion unique scents.

‘It’s actually a fairly simple arrangement to begin with,’ says Firestein.

‘The protein receptors are what capture odour molecules. It’s kind of like a lock and key arrangement, where you could think of the protein receptors as the lock, and the odour molecule is the key, and if it fits into the receptor, then it activates it.’

When the receptor is activated, it initiates a cascade of events inside the cell that causes ion channels to open, and the olfactory nerve to ‘fire’. However, after that things get more complicated. For a start, any given odour molecule may bind to anywhere between two to a dozen or more receptors at different affinities. In addition, any given receptor can recognise a few dozen odour molecules that are chemically similar.

Scientists have mapped the smell circuitry in the brain. The olfactory neurons in the nose project first to the olfactory bulb, and from there travel to another area of the brain called the piriform cortex, devoted to olfactory processing. However, what comes next, that is, how our brain interprets the sensory information it receives to build up a perception of a smell, is a mystery.

Scientists originally thought that if a person sniffed a rose, the blend of 280 different chemicals that make up the rose’s scent would travel up into the nose and activate a specific pattern of receptors, and that pattern of activation is what the brain would read, like a smell map. But this has turned out not to be the case.

‘We can’t find that pattern in the brain,’ says Firestein. ‘So, if you put a rose under your nose and then a piece of pizza under your nose, and you look in the brain, you can’t see a pattern difference. It’s just active all over the place.’

To make things more complicated, Firestein’s lab has shown that some odour molecules, and even certain scentless molecules, can block olfactory receptors, suppressing their activity.

‘If those chemicals are in a blend, then that will also change the perceptual quality of the smell, so it becomes very, very complicated. How the brain sorts this all out is, I think, one of the big questions, not just in olfaction, but in neuroscience in general,’ says Firestein.

One thing we do know is that the olfactory system is unique in its wiring. All our other sensory systems, ie sight, hearing, taste and touch, connect first to a part of the brain called the thalamus. The thalamus acts like a gatekeeper, filtering out unnecessary data, before the relevant information is sent out to the various parts of the cortex for processing. However, the olfactory system bypasses the thalamus completely. Instead, it goes directly to another area of the brain called the amygdala, known to be involved in emotional responses. It also has some direct connections to the hippocampus, the part of the brain responsible for memory formation and storage.

‘The olfactory system is the only sensory system to have a direct superhighway connection to the memory and emotional centres of the brain. All the other senses have to go through the brain’s side streets,’ says Leon.

It is conceivable that when one is experiencing something emotionally salient, such as a first kiss, the smells associated with the moment become tagged to the memory. This fits with what we know about how memories are formed, a process famously summed up as ‘neurons that fire together, wire together’. The direct connection between the olfaction system and amygdala could also explain why studies have found that, when compared with memories triggered by other senses, memories linked to smells tend to be more emotive [10] and more likely to extend further back into early childhood [11].

So, could you ever design a perfume to trigger happiness in anyone who sniffed it? As well as difficulties in mapping how the brain processes and responds to scents, another problem is the odours that trigger happy memories are unique to each person. While research shows some scents may have ‘universal’ interpretations to humans – a sweet-smelling rose almost always smells nice to everyone – with some scents, people’s perception can differ.

‘At one point, the army was trying to find a really bad odour they could use to disperse crowds,’ says Leon. ‘They tried cadaverine, a chemical emitted by dead mammals, but it didn’t work because if you’ve grown up in a house with dead mice below the floorboards, most of the time you regard cadaverine as a very pleasant, sweet odour, and it doesn’t bother you. Some people will smell the same odour and have a very different response.’

So perhaps we should take the perfume industry’s claims that they can design scents to trigger specific emotions with a whiff of healthy scepticism.

‘I think the idea you can put peppermint smells in an office complex where people are working away and they feel more energised at four o’clock in the afternoon – there’s no question that can certainly happen,’ says Firestein. ‘The opposite is true too – bad smells can certainly trigger emotional responses like disgust and even deeper ones, like psychological depression – there’s certainly evidence for that.’

‘But whether or not you can spray something on me, and I suddenly feel happy when I’ve just had some bad news, I’m less convinced.’

References

1. H. Harada et al, Front. Behav. Neurosci., 2018; DOI: 10.3389/fnbeh.2018.00241
2. F. Barati et al, Nephrourology Monthly, 2016; DOI: 10.5812/numonthly.38347
3. F. Ghorat et al, Iranian J. Med. Sci., 2016, 41 (3 supp), S13.
4. L. Hoult et al, Amer. J. Plant Sci., 2019; DOI: 10.4236/ajps.2019.106072
5. R.S. Herz, Brain Sci., 2016; DOI: 10.3390/brainsci6030022
6. C.C Woo et al, Front. Neurosci., 2023; DOI: 10.3389/fnins.2023.1200448
7. H. Cha et al, Geriatrics & Gerontology Int., 2022; DOI: 10.1111/ggi.14287
8. M. Leon et al, Mol. Neurosci., 2024; DOI: 10.3389/fnmol.2024.1455418
9. J.S Choi et al, JAMA Otolaryngol. Head & Neck Surg., 2021; DOI: 10.1001/jamaoto.2020.3502
10. R.S. Herz, Ann. New York Acad. Sci., 2006; DOI: 10.1111/j.1749-6632.1998.tb10643.x
11. A. N. Miles, D. Berntsen, Memory, 2011; DOI: 10.1080/09658211.2011.613847