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Smelling the city

By Fiona McWilliam
Urban design encompasses a wide range of issues, but smell is generally ignored. The author of a new book is keen to remedy the omission and get everybody to pay more attention to the ‘smellscape’.

Our sense of smell cannot be switched off, rather it draws in odours indiscriminately whether we
perceive these odours to be good or bad.

While we see can that the visual landscape is separate from our bodies and have some control over our engagement with it, explains Victoria Henshaw, a lecturer in urban design and planning at the University of Sheffield and author of the blog Smell and the City, we are constantly immersed in the ‘smellscape’ as we breathe in and out.

Sense of smell is much more important to people than they actually appreciate, Henshaw says. ‘It is sadly only when we lose our sense of smell (a condition called anosmia) that we truly appreciate the role it plays in connecting us with our surrounding environment, our friends and family, and in evaluating the everyday items that we encounter in our lives’.

She mentions how Fifth Sense UK, a charity for people with smell and taste disorders, found in a recent survey of its 485 members that 56% felt alone and isolated as a result of their condition and that 42 % suffered from depression.

‘Yet as it currently stands,’ Henshaw says, ‘smell environments generally exist as a by-product of other activities rather than having been created as an intended design for an area.’ As a result of this, she adds, ‘we get these weird scenarios where the most scented plants can be found in areas such as the central reservations of roads, or hanging baskets above people’s heads, where we can see but not smell the flowers’.

Scent has unique qualities, Henshaw argues: ‘It is ubiquitous, persistent and has an unparalleled connection to memory, but it is usually overlooked in discussions of sensory design’.

Through her work, which includes organising urban ‘smell walks’ both in the UK and further afield, odour advocate Henshaw is trying to get people to switch their attention to smell. ‘I like to take people to alleyways behind shopping streets which provides a good and surprising insight into how we organise our smell environment’. You can smell the products of a particular shop, Henshaw says, through ventilation systems – smells that include the dye from new clothing, ‘artificially inserted perfume’, or the immediately recognisable odours of pet shops and pharmacies.

Pollutants, ie those gases that can potentially harm humans or the environment (such as those included in vehicle exhaust fumes) can adversely affect our noses. People who live in cities, Henshaw says, generally have a poorer sense of smell than those who live in the countyside. And living in heavily polluted cities can cause permanent damage to one’s sense of smell.

Gases can mask subtler smells, including those of vegetation, and can even reduce scent trails for bees by about a third.

Yet there’s no such thing as a good or a bad smell, Henshaw insists, as our response to different smells is learnt. (Babies, she claims, like the smells of excrement and sweat, because they are familiar).

The only in-built preferences we have for smells, it seems, are associated with those ‘that tickle our trigeminal touch nerve (on page 47’). These include mint and potentially toxic substances such as nail polish remover, which some of us grow to love.

How we react to smells in the outside world is highly influenced by place: we expect different smells in different types of places, a country roadside for example, or a city square. ‘If a hotel room is next to a kitchen, we might find its smell disgusting,’ Henshaw says, ‘but it’s not, it’s just in the wrong place at the wrong time.’

Numerous smell surveys have explored smell preferences, and Henshaw mentions that when the US army tried to develop a universal stink bomb for dispersing crowds, they couldn’t find one single smell that all people disliked. That said, freshly baked bread is one of the most universally favoured aromas in the West.

Across the Western world, she says, smell is not only one of the most marginalised of the widely recognised five senses, but also the one that people are apparently most willing to lose. In 2008, a UK insurance company assigned a monetary value to the total loss of sense of smell of £14,500 to £19,100. This compared with £52,950 to £63,625 for the total loss of hearing, and up to £155,250 for the total loss of sight.

We have to look back in history to understand why smell is held in such low regard, Henshaw explains: in the 17th and 18th centuries, ‘the enlightenment marked a societal move towards a civilised and humane society which prioritised the “noble” sense of sight and hearing over the “lesser” senses of smell, touch and taste’ – an approach ‘which became contained within physical built environmental form’.

The enlightenment also heralded ‘a view of the natural role of women as being determined through physical and biological factors,’ she adds, ‘and the senses of smell, touch and taste became seen as feminine and “witch-like”’. They were also associated with ‘the working masses, ethnic minorities, the elderly and those living and working in the rural hinterlands’.

The prioritisation of vision in particular over the other senses was, Henshaw argues, fully embraced by modernism, ‘leading to the further rejection of positive roles for odour in progressive, high-quality urban environments’, in which designers ‘seek to suppress smells’.

She believes that smell should be ‘pro-actively considered’ in the delivery of areas where people can escape from the stresses of modern life. She has identified a range of ‘tools’ by which odour might be better considered as part of the design and management of the urban environment. Outlined in her new book Urban Smellscapes: Understanding and designing city smell environments, these relate to air movement and microclimates, activity density and concentration, materials and topography. These are all factors, Henshaw says, that are currently considered as part of existing design, development or management practice, and so ‘a wider, more holistic sensory approach to design could therefore easily
be incorporated into existing practices’.

How designers respond has to be ‘area appropriate’, she explains. For example, near a busy road they could perhaps encourage air movement while in enclosed areas with cafes and restaurants or fragrant planting, they could design buildings in a way that enables smells to concentrate.

‘One of the key things for designers to recognise are the smells that are already there, which can be revealing of the identity or history of a place, and which could be reinforced by visual or sound prompts.’

In her book, Henshaw notes that although ‘soundscape perception’ has a significant role in restorative experiences of urban parks, the number of studies examining any potential restorative effects offered by urban smellscapes remains limited.

When considering the key roles that smell plays in aromatherapy treatments and relaxation sessions at spas, she says, its omission from the majority of restorative environmental research ‘illustrates how markedly neglectful our cultural attitude is regarding odour, the roles it can play and the places where it belongs’.

Sensory gardens can provide great examples of where smell has been incorporated as a positive element in landscape or environmental design, Henshaw says, ‘but in my view these are few and far between and we need to think more proactively about the pleasures to be gained via smell and some of the other senses, such as the textures, taste and sound in more mainstream design practices.’

And while allergies will always have an influence on a small proportion of the population, she adds, ‘I actually believe that in our current practices, we deodorise environments far too much and as a result, make people less resistant to allergies through the resulting limited exposure.

‘In thinking more proactively about smells in our designs, we might create more human environments and places that better meet our sensory needs’.

How our olfactory system works

It is only in recent years, claims Victoria Henshaw, that a dominant theory has been widely accepted by the scientific community about how our sense of smell works.

‘The sense of smell functions by drawing information from two key smell sensing organs; olfactory receptors provide the primary source for detection, with additional information provided through the trigeminal nerve.’

When a smell is inhaled, Henshaw adds, it travels through the nose and is dissolved in nasal mucus. Information is passed through neurons to the olfactory receptors and to the olfactory bulb which is located in the limbic system, otherwise known as the brain’s ‘emotional centre’. This relays information to other parts of the brain to form a pattern, and it is this pattern that the brain recognises, drawing from previous memories of encounters with that odour.

The olfactory receptors enable the average person to differentiate between approximately 10,000 different smells, and while normally a human can detect odours in concentrations as low as a few parts per billion (when diluted in air), other animals can detect much lower concentration levels. Dogs, for example, can identify smells somewhere between 1,000 and 10,000 times better than humans can, while polar bears can detect a seal from more than a kilometre away.

‘The second, lesser known element of the sense of smell,’ writes Henshaw in her book Urban Smellscapes, ‘is the trigeminal nerve, which is the nerve responsible for sensation to the face’.

Olfactory nerve endings on the trigeminal nerve can detect even very low concentrations of odours that produce bodily sensations, typically the tingling and hot or cold feelings associated with substances such as petrol, paint, nail-varnish remover and many toxic chemicals. Some substances have odours detectable only through the trigeminal nerve, including a number of air pollutants.

‘Most odours have some trigeminal element to them,’ Henshaw explains, ‘this is what makes some people’s eyes water when peeling onions, or causes them to sneeze when smelling pepper’.

The ability to detect an odour and the way that odour is perceived can vary, she adds, ‘according to the characteristics of the smell, the characteristics of the individual detecting it and the environment’.
She summarises these sources of variation
in the diagram above.

Henshaw writes that over time, recollection and identification of odours has been shown to be much more consistent than that of visual images, and ‘once we have formulated memories of odours, we are very likely to retain them’.

Anosmia, the inability to perceive odour, is caused by inflammation of the nasal mucosa; blockage of nasal passages or a destruction of one temporal lobe. It can be temporary, but traumatic anosmia, caused for example by a blow to the head, can be permanent.

Further reading

Urban Smellscapes: Understanding and designing city smell environments, by Victoria Henshaw (Routledge, 2014).

Invisible Architecture: Experiencing places through the sense of smell, by Anna Barbara and Anthony Perliss, (Skira Editore, 2006).

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