So, we all have five viruses living in or on us...without causing any problems. We have a normal viral flora.
And one of the common "normal" viruses is adenovirus. If that seems familiar, it's because it's a very common virus that we all have to deal with - the common cold.
As we all know, the symptoms of a cold and the symptoms of an allergy attack are, well, very similar. But it's always the assumption that, oh, adenovirus makes us sick.
Except it doesn't. Not always. It may be that when things are working the way they should, adenovirus just...hangs out. It doesn't cause us any major problems, although it probably doesn't give us any benefits either. Or does it? Right now, we don't know whether these viruses should be considered symbiotes (meaning they "pay the rent" in some way) or exploitative parasites.
But here's what got me to thinking. What if the common cold and certain types of allergic reactions have the same basic symptoms because the common cold is an allergic reaction - our immune system reacting to what should be a normal part of our own biome? Or a reaction to something from somebody else's that doesn't quite work? (Or, it could be that mutations mess up whatever "deal" we have with the virus).
Just a thought.