system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Allergies are caused by an immune system overreaction. Why can’t immunosuppressant drugs like Humira be used to prevent allergic reactions?
gpt
There are a few reasons. First, Humira targets a different part of the immune system than is triggered by allergies. Histamine is one of the most common immune signals for allergic responses, so most allergy meds block histamine signaling in some aspect. Humira blocks "Tumor Necrosis Factor" (TNF) signaling which is involved in viral infections, inducing fevers, cancer, and auto immune based inflammation.

Second, Humira has a much greater risk of severe side effects compared to over the counter allergy meds. This is because TNF signaling being used for a wider range of the immune system.