Why is there a distinction between an *allergic* and an *immune* response?
The trouble is, you can't live without being exposed to all sorts of non-self particles. Some of those particles signal an actual threat to your health (proteins associated with a disease causing virus), some are nearly harmless (bee stings), some are completely harmless (grass pollen or cat dander), and some are potentially valuable as part of a food substance (seafood or peanuts). Ideally you'd like your immune system to respond to the harmful ones, and ignore the harmless or useful ones. An allergy is defined as an unneccesary immune response to a harmless (or nearly harmless) substance.
You do want your immune system to deactivate venom from a bee sting, but you don't want it to react so strongly that as a side effect your throat swells up and you can't breathe. Most people breath in grass pollen every day of their live with no ill effects, so those folks who have an allergy to grass pollen are being made miserable by their immune system to no good purpose.
Ideally the immune system mounts a full response only when the presence of particular non-self particles is associated with other signals indicating that something &quot;bad&quot; is happening which merits an immune response. However, the process by which the immune system is regulated is incredibly complex, involving feedback loops from hundreds of different chemical pathways and dozens of different cell types. The process is imperfect. Sometimes it goes wrong, and the immune system mounts an aggressive response to a harmless foreign substance or even worse part of your own body.