To my understanding, an allergy is a hypersensitivity of the immune system causing a substance in the environment to be identified as pathogenic by the immune system while it is not pathogenic. During an allergic reaction, the immune system triggers histamine, which triggers an inflammatory response just as if the allergen was a pathogen. The resulting symptoms of an allergic response is similar to the symptoms of a cold but without fever.
To my understanding a fever is an increase in body temperature driven by the body through production of pyrogens, most often in response to a pathogen. This response might be adaptive for various reasons that I am not too interested in discussing here.
According to NIH, an allergic response never causes a fever. Given that the fever is not directly caused by the pathogen but rather is caused by the body, why do allergies not cause fever?
The fact that allergies don't cause fever give me the weird impression that the immune system somewhat "understand" the allergen is not pathogenic otherwise the immune response would be the same in the case of an allergen or a pathogen.
Allergic responses implies the firing of IgE. IgE are typically involved in response to parasites such as helminths. Could it be that pathogens leading to an immune responses mediated via IgE never yield to fever. Why would it be the case?
Plasmodium falciparum (which causes malaria) is a pathogen who causes an immune response involving IgE (according to the wikipedia). Malaria's symptoms include high fever (according to Mayo Clinic). Now it would be possible that the pyrogen would be of external origin (not produced by the body but by the pathogen) or it is possible that several immunoglobulin are involved in response to P. falciparum. The same logic hold for Fasciola hepatica (an helminth; common liver fluke) who also causes fever and is who's infection lead to the firing of IgE.