Allergies - Symptoms from Allergenic Particles How asthma and allergies are triggered by allergens by Steven Temes

If the nasal sinuses are the site of an allergic response, you can still breathe through your mouth; if the inflammatory response is in the upper respiratory tract, the air passages are wide enough to accommodate some swelling (wheezing); when you get into the lower respiratory region (bronchioles and alveoli) where the diameter of the air passage is narrower, inflammation can result in more complete obstruction of air flow and reduction of gas exchange.

Factors that come to mind with regard to allergic response are the degree to which a mucous membrane is protected from direct contact with an allergen or irritant (why allergies can be worse in low RH) and the blood supply in the local tissue required to produce the full- blown immune response.
The discussion of surface-to-mass ratio of allergenic particles is also important to consider. In any case, it seems that the greater the surface area within the respiratory tract that allergens or irritants can come in contact with, the greater the potential health risk.
On the topic, of sensitization and the apparent coincidence that the most affected individuals live in the dirtiest houses, I would like to add that it is the very specific allergens or chemical sensitizers in an individual's environment that produce the hypersensitivity response. Chronic exposure to low levels of a particular species of mold, for example, can result in a hypersensitivity reaction to this one particular species. I was told by clients who had to move out of their house due to a child's asthmatic reaction to major mold contamination that, surprisingly, the child could tolerate his grandmother's moldy basement without similar effects. If he went back into the first mold-contaminated house, he could not breathe.
Exposure increases when particles stay suspended longer and when there is more contact with the "immune system" on surfaces in the respiratory tract, and so does the potential to become sensitized or react immunologically (antigen-specific antibodies) or with an irritant inflammatory response (RADS). It isn't just coincidence that many people with allergy problems live in dirty houses - it may be causative. Of course, who actually becomes sensitized is genetically pre-determined which is why lots of people live in dirty houses without any problems and don't really learn how to clean thoroughly until they do have problems.