Hello,
It seems to me that logically, antihistamines have to reduce the body's ability to fight off a cold or infection.
For example...
Let's say I have 2 events taking place in my body at the same time.
Event 1: On Monday I contract a cold virus from my girlfriend and start showing symptoms. My understanding of one of the many things that is taking place inside me is that my granulocytes and other things are releasing histamine to fight this virus. The purpose of this histamine is to signal to other antibodies "Hey buddies, I need some help over here". The other antibodies get this message and come help fight the virus.
Event 2: On Wednesday, I go over to a friends house that has a bunch of cats, which I am allergic to. Because of my allergic reaction, I take an antihistamine such as Benadryl. Again, my understanding of the allergic reaction in my body is that it has incorrectly identified whatever it is that comes from cats as something that needs to be fought off, much like the virus in event 1. Part of this process is the release of histamine, again, just like event 1. So, I took the Benadryl to suppress this histamine release, thereby reducing my discomfort.
So the question is, if the Benadryl suppresses the histamine for the cat stuff, doesn't it also suppress the part that is helping fight the virus? If so, isn't the Benadryl, in effect, suppressing my ability to fight the virus?