system
Given the following post, respond as if you're commenting on Reddit:
human
Why are there pills for some allergies but not others? Example: there are pills for seasonal allergies but not for peanut allergies.

Got my first mosquito bite of the summer today! Itches like a mother lover. I applied some anti-itch cream which seemed to help, but I couldn't help but wonder why we have pills for certain types of allergies and not for, say, a mosquito saliva allergy.

Am I missing something here? Are all allergies really that different? If so what makes them that way?
gpt
There are.  


The problem with some allergic reactions eg peanuts, is the rate of onset of the reaction.  This is mostly due to either the concentration of the the allergen or the host's sensitivity to a particular allergen.  

Your seasonal allergy medicine is designed to work against a relatively low level of physiological reaction (low concentration of antigen or lower immune response).  Meanwhile, high dose epinephrine (eg. EpiPen) can counter the inflammatory response to a high level allergic reaction. 

The main reason that we don't take those medications on a continual preventative basis is that the side effects include all sorts of bad things up to and including cardiac arrest.  So most of the time, people are better off waiting until they start having a reaction and then taking their medicine, if they have a known allergy problem.