Every other sense routes through the thalamus, which acts as a relay and, functionally, as an editor. Visual and auditory information is sorted, prioritised and rationalised before the emotional centres of the brain get a look at it. By the time you have consciously noticed a shop's music, you have already evaluated it.
Olfaction does not work that way. Signals from the olfactory bulb pass directly to the amygdala and the hippocampus — the structures responsible for emotion and associative memory — before any rational filter is applied. Scent is registered as feeling first and identified as information second, if at all.
The commercial consequence
This is why a fragrance can change how a room feels to someone who never consciously noticed there was a fragrance. It is also why scent-linked memories are recalled more vividly and more emotionally than memories cued by a photograph or a jingle.
For a business, that means a signature scent is doing something no other brand asset can do: attaching an emotional state to a place, below the level at which the visitor is evaluating your marketing. It bypasses the scepticism that a logo, a slogan or an advert has to fight through.
Why it has to be deliberate
The corollary is uncomfortable. Every space already smells of something, and that something is already being encoded emotionally. A lobby that smells of cleaning chemistry and carpet is forming an association just as efficiently as one that smells of saffron and amber.
Choosing not to manage the air is not a neutral decision. It is a decision to let the building's incidental smells write your brand's emotional footnote for you.