Chemicals in the inhaled air dissolved in the epithelium that is the Olfactory bulb or nasal bulb which is a receptor. There the chemical energy converts into electrical energy (Action potential) and passes through the Olfactory nerve to olfactory cortex of the brain (Frontotemporal junction). This triggers the release of neurotransmitters like “Serotonin” and “Dopamine” which regulates the mood. Smell is the only function which directly goes to the limbic system.
As a habit, if the dust particles are absorbed but not removed naturally with the common cold, fever and another way of toxic removal happen. Hence cleaning of the Nasal passage is required to prevent future nasal allergy or bronchitis or bronchiectasis or asthma.