Many haunting cases involve witnesses smelling unlikely or unusual smells with no obvious source. The range is wide, from the odour of flowers and perfumes to foul or putrid smells. Though often part of a wider set of 'symptoms' of a haunting, unexplained smells on their own are sometimes interpreted as indicating a 'ghostly presence'.
Smell is a notoriously difficult sense to measure. Indeed, there is still a strong controversy about what how it works! Some scientists maintain that it is the shape of molecules that allow them to connect to particular sensors in the nose and so stimulate a nerve. Others, a growing minority, say it is to do with the quantum state of the molecule being sensed.
As with other senses, odour perception varies between individuals. This can lead to disagreement between people on the identity or even the presence of a particular smell. Despite an image of being poorly developed in humans, our sense of smell is surprisingly sensitive. However, just as we stop hearing a constant background noise, persistent smells stop being noticeable after long exposure. As with the other senses, actual smell perception happens in the brain, not the nose, so misperception is possible.
Investigating paranormal smells
Unfortunately, investigating paranormal smells is difficult. There are no easily available cheap instruments to detect or measure them. In almost all cases, investigators must rely on their own sense of smell and reports from witnesses. This is difficult when people vary a lot in their perception of smell. These factors alone may be responsible for some reports of apparently paranormal smells. If one person persistently reports a smell that others can't detect, because their sense of smell is particularly sensitive, it may give the impression of being a paranormal phenomenon.
Finding odour sources
A frequent reason for smells to be reported as paranormal is when they have no obvious source. However, it can even be difficult to track down 'normal' smells with a perfectly real source. We usually assume that a smell will be strongest near its source and use this to track it. However, there are many factors that affect the position and concentration of a smell. Furthermore, if an odour is evenly distributed in the air, as can happen sometimes, tracing its source becomes a matter of pure luck!
Even in perfectly still air, an odour will disperse from its source by a process of diffusion. More often, however, air is moving as a result of convection currents, draughts, winds and so on. Such air currents can move, disperse and even concentrate a smell so that finding its source becomes difficult or impossible*.
To see how this can happen, imagine a river with thousands of tiny wooden sticks floating on top of it. In the middle of the stream there is a strong constant current and the sticks move quickly and freely, with the sticks generally maintaining a constant distance from one another. But by the banks there may be areas where the water is relatively static, caught in a bay or bend for instance. Here sticks may move in a circle or even stop completely, often forming clumps.
The same thing can happen in air with smells swept along by an air current. Some smells may be moved and dispersed rapidly. They can also be concentrated in certain places, like alcoves or the corners of rooms, where air currents are sluggish. With the fast moving smells, it is difficult to trace the source because the concentration of odours remains much the same along the entire length of the air current. And in areas where the air current is sluggish, the smell may be concentrated as if there was a source present, even when there is not.
Smells can also be remarkably persistent, especially when undisturbed, long after their source has completely gone. Consider the following real life example. "I toasted some crumpets, which produce a distinctive, easily recognizable smell. Afterwards I left the house, returning only after two hours. I could smell nothing of note on my return. Then, suddenly, I smelt the crumpets again right in the very centre of a room that I had already traversed several times since my return. What had changed is that I had opened a window in the meantime. Evidently the breeze from the window had moved a pocket of the smell that still remained somewhere, perhaps in some undisturbed corner, into the centre of a room. The smell certainly didn't originate outside!"
In this example most of the smell clearly dispersed during the two hours in which the closed house was empty. However, at least one concentrated area of the smell apparently remained. The breeze from the window then moved this 'pocket' of smell into the centre of a room. Someone arriving in the house with no knowledge of crumpets having been toasted might have been puzzled when the smell apparently just appeared without obvious cause! It could have been interpreted as the work of a ghostly 'presence'.
Smells can also obviously arrive from elsewhere, when blown along by air currents, so that there is no nearby source can be found. If you leave lots of windows open in your house in summer, smells can easily drift in and, in the sluggish air currents inside the building, become concentrated. No amount of searching the house will discover any source to the smell.
As well as smells with no obvious source, another reason an odour might sometimes be considered paranormal is if there is NO POSSIBLE source in the vicinity. So, if someone smells a perfume that no one present is wearing, or even owns, it could be considered to indicate a ghostly presence. There are possible natural explanations to such circumstances which need to be considered first, however.
Firstly, as mentioned above, smells can persist for hours after their source is gone, and they can move long distances or be concentrated by air currents. So even if no one present has a particular perfume, maybe someone in the building an hour or two before did! Or perhaps someone in an adjacent building is standing near an open window!
Secondly, unlikely smells can be generated by an unusual coincidence. For instance, some materials only emit a noticeable smell when heated, so it is worth checking if an odour's appearence coincided with a temperature increase. And sometimes if two odours are produced at the same time, when normally they only appear singly, the mixture could smell completely different. Perfumes are made by mixing ingredients (essential oils) to produce new, distinctive smells. A mixture of two odours can smell quite different to either constituent.
Smell as a spookiness factor
Smells can invoke emotional responses and even trigger memories (particularly evoking recollections of the first time the smell was encountered, for instance). Just as 'spookiness factors', like low lighting, high humidity and low temperature, appear to encourage reports of haunting phenomena, certain smells (such as from old buildings) may promote paranormal reports.
Smells can psychologically prime people towards particular responses to situations. Amazingly, this can happen even if the concentration of the smell is too low for the witness to even notice it! Research has shown that people react differently to the smell of human sweat when it is produced in a stressful situation as compared to from exercise. Effectively, people really can smell other's fear! If people enter a room recently vacated by people who were scared, they might feel anxious themselves for no obvious reason! This could conceivably be a factor on ghost vigils!
When one individual persistently reports smells that no one else can sense, it could indicate a medical problem, like phantosmia. This is certainly something that should be considered seriously alongside possible paranormal explanations.
*Air currents indoors can be highly complex and very localized. See this video for a demonstration of dust/orbs moving in localized air currents.
© Maurice Townsend 2011