Short answer
When you are exposed to the same scent for a long time, your sensitivity to that scent temporarily decreases. This is often called olfactory adaptation or habituation. The scent may still be present while you perceive it less consciously.
Your brain filters constant information
Our senses are sensitive to change. After a while you barely feel a watch, constant background noises fade from attention and the same happens with scent.
With continuous or repeated exposure, the perceived intensity drops. Both processes in the olfactory system and central habituation play a role.
That is why your own home smells different after a holiday
When you leave a space for a moment and come back later, the scent is often suddenly clear again. Your olfactory system has had time to recover from the continuous exposure.
The same happens with personal perfume and signature scents in the office.
The dangerous reflex: turning it up
For professional scent marketing, this is important. After a few hours, employees may think the machine is barely working and increase the intensity.
A new customer who has just walked in does not have that habituation and may then experience the space as very heavily perfumed.
How do you check the real intensity?
Have someone who has been outside the space for a while come in. Or step outside into fresh air for a few minutes yourself before assessing again.
In addition, use fixed device settings as a reference and don't keep changing them based on feel.
Coffee beans don't magically reset your nose
In perfumeries, coffee beans are sometimes offered as a "nose reset". Fresh, low-odour air is generally the simplest way to reduce olfactory overload. Adding a new strong scent can actually provide extra stimuli.
Habituation is not the same as loss of smell
If you only smell a familiar background scent less, habituation is likely. When you suddenly can no longer perceive several everyday scents, there may be a smell disorder and medical assessment is wise if this persists or is unexplained.