How bad smells affect your health

That foul odour wafting your way can do more than make you gag – it could also affect your body and mind.

For Elaine Corner, stepping into her garden on a summer's day can be unbearable. She likens it to "walking behind an open bin lorry". Even with all the windows shut in her home in the English market town of Westbury, the retired teacher says she still often can't escape the nausea-inducing stench from a nearby waste treatment plant. "We can't use our garden or go for a walk, you feel as though you're going to vomit," says Corner. 

At some point, we've all caught the rank waft of decomposing waste as we take out the refuse, drive past a rubbish dump or encounter the sickly pong from a factory. Just imagine living constantly with such a stench. 

Yet we give little attention to the health and quality-of-life impacts of such odour pollution. Bad smells are often dismissed as subjective or trivial. Research shows people typically value their sense of smell less than vision, hearing, touch and taste. Some US college students have even admitted they would rather lose their sense of smell than their phone.

It's not just the discomfort that people experience from living with terrible smells: studies link unpleasant odours in urban areas to health complaints ranging from headaches and nausea to difficulty breathing or disturbed sleep. They can also have long-lasting mental and physiological effects. A growing body of research is helping us understand the surprisingly significant role scent plays in the health of our bodies and minds.

The scent of danger

Smell has partly evolved into an early-warning signal to help us avoid a getting ill or infected. Something that smells rancid is likely to be packed with bacteria looking to do us harm. As such, it is part of our so-called behavioural immune system, says Johan Lundström, a professor in the science of smell at the Karolinska Institute in Stockholm, Sweden. "The olfactory system primarily functions as an avoiding system to learn to warn us about danger in the environment," says Lundström. His work has even shown that odour signals are processed in the brain within about 300 milliseconds of being inhaled through the nose. Study participants exposed to the bad smells showed a rapid physical response, instinctively withdrawing from the source of the smell.

Smell's defensive default makes it surprisingly easy to convince someone that an odour is negative, even if it's normally considered pleasant. "If we detect an odour and we don't know what it is, it's almost always a negative experience," says Lundström.

When a smell is associated with a threat, our sensitivity to it can also increase dramatically. In one study, Lundström and his colleagues showed that pairing a smell with an electric shock can make people detect that odour at much lower concentrations – a response that likely evolved to help humans react quickly to potential dangers, even when the smells are only faint. Similarly, the rotten eggs scent of hydrogen sulfide, a gas produced in sewage processing, can be perceived in concentrations as low as 0.5 parts per billion – an alarm bell for a gas that is lethal in higher concentrations.

Real health impacts

Smell isn't just about threat detection: odours can have very real effects on people's health and well-being. Scientists have shown that good smells, like the fragrance of a woodland, can be beneficial for our mental health, partly because they stimulate brain regions linked to emotion and memory. 

There is also evidence that the opposite can be true, with malodours damaging our health, although scientists are still trying to disentangle the precise link between odour pollution and any direct physiological impacts. A 2021 review of studies found some "biological plausibility" behind symptoms like headache or vomiting caused by bad smells. For instance, nasty odours can trigger the vagus nerve, a key part of the nervous system linking the brain and gut, making one feel sick or nauseous. But the scientists behind that review ultimately concluded that more research into the physiological impacts of smells is needed to draw clear-cut conclusions.

The extent of the affect on our health also depends on how worried we are by the odour. "The health impact is mediated through an individual dislike or fear of an odour," says Pamela Dalton, a cognitive psychologist at the Monell Chemical Senses Center in Philadelphia, in the US, who has spent 32 years investigating the health impacts of odours. The more anxious you are about an odour, the more it can impact your health and wellbeing.

Lifestyle changes

A persistent bad smell can seep into many parts of life. It can push someone to make lifestyle changes, which can, in turn, be harmful to their health. These changes are known as "maladaptive actions”. For instance, one may feel compelled to keep windows shut on a hot day or avoid going outside to exercise or spend time with friends. Living with the stink in Westbury, "affects your social life," Corner says. "If you're planning a barbecue in the summer, you're hoping it's not going to stink you out."

Serenity Strull/ BBC/ Getty Images

Still, the merest whiff of stench may be intolerable for some people, but for others, it can be barely noticeable. "There will be a wide range of responses; some will say they smell it occasionally, or it just doesn't bother them," says Dalton, who regularly investigates odour complaints. Age, gender, allergies and lifestyle choices like smoking are all among the factors how people perceive odours.

You may hope that people could just get used to an unpleasant smell over time, but repeated exposure to unpleasant odours, such as those from landfill, doesn't necessarily make them easier to tolerate.

In contrast, it is normal to habituate to neutral or pleasant smells. "Once you have smelt an odour, and identified that it's not going to kill you, then you stop being able to smell it," says Lundström. This is also why people, despite the human nose being able to detect one trillion odours, generally find it more difficult to name smells from things that aren't dangerous. Sniff tests suggest that less than half of us may be able to correctly name everyday odours like coffee or vanilla, for instance.

Fighting a stink

A stench can sometimes come and go – often with the prevailing wind – or may be noticeable only in some parts of any given neighbourhood. "It can be hyperlocal," says Amanda Giang, associate professor of environmental modelling and policy at the University of British Columbia, in Canada, who has investigated the impacts of odour pollution on residents in Vancouver. "I could live a block away and never know that the block over it smells like rotting fish."

But not all stenches are experienced equally: disadvantaged neighbourhoods, with cheaper housing, are often closer to stinky landfill sites or heavy industry. Studies conducted in Europe and the UK suggest that in some countries, people from low-income communities are more likely to live within a 1.25 mile (2km) radius of waste incinerators, landfills and hazardous waste sites than those with higher incomes.

Complaints about horrible smells can provoke change: sites ranging from sewage plants to fish processing factories have been forced to scale down or stop their operations, following campaigning from residents. There are also growing, but uneven efforts in countries around the globe to better control odour pollution, from a new regulation on odours from fish feed plants in Chile, to tougher rules on how much stink companies are allowed to make in residential areas in Lithuania. 

Odorous benefits

For those living in a neighbourhood plagued by unpleasant odours, life can be difficult, but there is at least one small consolation: having a well-functioning sense of smell is an important part of good health.

Research has shown that people with a keener sense of smell take greater enjoyment from eating, and even sex: in a 2018 study of 70 adults, those with high olfactory sensitivity reported greater pleasure from sexual activities and, among those, women also reported a higher frequency of orgasms during sexual intercourse. 

By contrast, the estimated 5% of people who lack a sense of smell – known as smell blindness or anosmia – often face wide-ranging health impacts. Interviews with people with anosmia suggest they feel they are at higher risk of having impaired appetite and a poor quality diet because of difficulties enjoying their meals. "If you lose your sense of smell, you will notice that your appetite goes away," says Lundström.

Worse still, research connects a poor sense of smell with a 46% higher risk of dying within 10 years among older adults. Scientists are still trying to explain why this is the case, although they see links with deaths from cardiovascular disease and neurodegenerative diseases like Alzheimer's and Parkinson's. 

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"As someone who's researched odours for decades," says Dalton, "I don't mind smelling bad odours because it means my sense of smell is really working!" 

Of course, it may not feel that way for the likes of Corner in Westbury. Hills Waste Solutions, the site's operator, said it is working with the Environment Agency to address odour concerns. 

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