Yep, they can affect the gut. Tho my main symptoms are brainfog & fatigue. The way to retire histamine symptoms is to go low-histamine for a while, then carefully reintroduce: https://www.histamineintolerance.org.uk/about/the-food-diary/the-food-list/ It looked a big challenge at first, but doing it has proved easy because the results are pretty good. My only remaining problem is my L. rhamnosus yogurt - it's the great gut-stabiliser, but it also generates histamine. So I have sometimes fixed my gut & given myself histamine symptoms simultaneously. But finding that balance is a relatively minor problem.