Antihistamines as child? (Allergy medicine)

[berlin1984]

I had them for hay fever, usually Cetirizine.

Random example from forum:

I sure tried some anti-histamine.  I had experience with them, since I had severe hay fever as a child. 

To clarify: I don't want to say antihistamines cause POIS. It could also be that POISers have more allergies in general (if they do, unproven idea..)

Some links:
Child hood antihistamine usage associated with ADHD?
Antihistamines (not all of them) are anticholinergic (we had this topic on the forum somewhere)

[Prospero]

Yes, chronic use of desloratadine during a few years, against eczema when I was young, then against bathing-induced urticaria in my teen years, and I got POIS around the time I stopped taking it. Eczema is still there, though less virulent. Quite a few people are in this case, if I remember well.
In addition to the links you mentioned, someone had a theory about chronic H1 antihistamine use causing upregulation of H1 histamine receptors, generating other consequences (may be linked to opioid topic, etc.). As you point out, it may also be that Poisers are more prone to allergies. Waldinger, notably, had noticed that most of his Pois patients had an atopic skin.

[Journey]

I never took any antihistamines until I learned they might help POIS and I tried them for first time in my life at 19 so no and I still got POIS at puberty