She says that smell is quite unlike any of our other senses because it’s the only one that can bypass the blood/brain barrier to the central nervous system – meaning that the brain can register aroma twice as quickly as it does pain.
‘Through the olfactory system (the network that allows us to smell), scent molecules have direct access to the brain’s limbic system, which is the centre of our memories and emotions,’ Gemma says.
Source: Why scents can evoke different emotions and memories | Metro News