[barkbro]

This would explain contact alleries to for example nickel and various chemicals, which are usually quite harmful, but I don't see how this would explain pollen and animal allergies. A lot of the pollens that cause allergy in some people are coming from harmless plants. And with pollen spreading in the wind, it would be an annoyance without necessarily protecting people much against coming in contact with the plants. Would avoiding contact with certain animals be beneficial? Other than avoiding pathogens, I don't see a lot of reasons to do so.

Anyway, I wouldn't be surprised if allergy, like many things in biology, are caused by multiple factors instead of just one.

[fixermark]

If I'm understanding correctly, the overall hypothesis is that the allergy response is triggered by exposure to other toxins at low levels that prime the immune system to respond to the toxin, but the priming is inaccurate; the histamine-generating machinery does a quick-and-dirty approximation of the chemical that triggered the cellular damage, and while rounding up whatever industrial monomer irritated your nasal passages, it also snags the molecular tags of surrounding pollen and other common chemicals.

As a side-effect, the system gets primed against the actual threat but also primed against benign foreign chemicals as well. The change in the ecosystem that has caused this defense mechanism to become a hindrance is the introduction of novel chemicals to our daily lives that trip low levels of immuno-response (or increase in chronic exposure to those chemicals due to a general shift to indoor living, where the chemicals just sit in the environment and bathe us in them), providing the opportunity for the immune system to sensitize to frequenltly-contacted benign chemicals.