I am pleased to report that after 3 years of suffering I have cracked the histamine intolerance. I now know why my recover has been so slow and why I would relapse in such spectacular fashion. It also explains why my condition got so much worse and the cardiovascular and skin problems started just as the gut issues went away.

What I found out is truly astonishing: The 24 hour antihistamines (Allegra, Claritin, and Zyrtec) have been responsible for the "relapses" and the slow recovery. I have been suspecting them for some time but had to have incontrovertible proof to come to such a conclusion. It really became clear after I had a bad reaction to some chicken that I accidentally stored in my fridge at 47 degrees (it caused 2 urgent care visits). I took 2 Claritin and it was WORSE on the 2nd day! I couldn't understand. I thought the reactions lasted 1 week because I would have to slowly wean myself off the antihistamines for that period when I took them after an attack. Turns out they only last 24 (in some rare cases 48) hours if I just take Benadryl. Things became obvious when I tried Zyrtec. Zyrtec worked really well at first but then things really deteriorated and I was getting red blotches and hives even without eating anything. I suddenly could not eat bananas, chicken, tomatoes, walnuts, and cashews when I could eat them before. When I took a 2nd one things really went nuts. I got red blotches all over my face within 30 minutes, my ears started ringing from the vasodilation, and I had to take Benadryl for a nighttime attack. I thought back to how many times I had had a severe attacks (ones so bad I could where I remember exactly where I was and what I had eaten) while on them. Pretty much every, single, time.

Since the antihistamines are not DAO blockers, have different molecular structures, and caused things to eventually fall apart with greater intensity the better they worked initially -I can only conclude that H1 receptor signaling in the gut is needed to release DAO. I have stopped using the antihistamines now and just take Benadryl when I have an attack; and I have been recovering weekly -almost daily! I am close to eating normally and only have attacks when I eat something really loaded with histamine (2 recent examples are from a hard-boiled egg that was left at room temperature for over an hour, and chocolate with chocolate liquor in it -which is fermented).

My guess is that I am not completely better because I now have reduced H1 receptor expression in my gut from the antihistamines and it will take some time to get that back. That also explains why my gut symptoms disappeared just as it got worse everywhere else. It's a pity that doctors would not believe me because this is a very promising avenue for research and could relieve a lot of suffering in others who have this. It could also serve as a test for it.