My son has problems with histamine producing gut bacteria, and we have found out how to deal with it.
The DAO and HNMT enzyme pathways can deal with your histamine if you take supplements so that they have the cofactors they need.
Here is a list of the cofactors:
Niacinamide (if you don't have enough niacin the product of DAO, which is an aldehyde, builds up and causes a negative feedback loop which inhibits DAO production. When this happens people think they can't make DAO when really they can. You have to take 500-2000mg three times a day with meals depending on how much histamine the bacteria are producing.
B6 or P5P, we use about 50-100 mg P5P
magnesium 400-1000 mg a day
Vitamin C 1-2 grams with meals
For the histamine N-methyltranserase HNMT pathway you need to support SAMe production by taking either folinic acid or methylfolate and B12. The sublingual methyl B12 is good.
It isn't unusual for these vitamins to work good for a few days and then you need more niacinamide. This is because the mechanism for regulating SAMe takes a few days to adjust and while it is adjusting the HNMT pathway is getting rid of more of the histamine than it does after it adjusts. It would take a long explanation to tell you why so I am not going to explain but I am just putting it here so that if you try it and it happens you won't say, "this doesn't work after all!" when you really just need to adjust the dosages.