Oranges are a histamine liberator: the citrus prompts your body to release its own stored histamine, so you get the itching, hives or flushing of a histamine reaction even though the fruit itself is low in histamine. They are also high in salicylates, which is a separate trigger for some people.

Yes, and this trips a lot of people up. Lemon is a histamine liberator, meaning it triggers your own mast cells to release histamine even though the fruit contains very little. The resulting hives, itching or flushing come from your released histamine, so a food being low-histamine does not protect you if you are liberator-sensitive.

No. Egg grades clean for histamine content and is not graded as a histamine liberator, so plain egg is usually fine on a low-histamine diet. If eggs upset you, look at the company they keep: the aged cheese in the omelette, the leftover cooked egg that sat in the fridge for days, or a genuine egg allergy, none of which are histamine problems with the egg itself.

Being nutritious and being low-trigger are two different things. Spinach grades high in histamine and is a moderate histamine liberator, so in histamine intolerance it can still set off itching, flushing or headaches regardless of how good its vitamin content is.

Fresh tomato grades high for histamine and high as a liberator, so it hits from both directions. Processed tomato is worse rather than equivalent: our data grades tomato sauce at the top of the histamine scale and high for oxalate as well, because reducing and storing concentrates the fruit and gives amines time to build. On a strict low-histamine trial, jarred sauces, passata, ketchup and sun-dried tomatoes are the versions to remove first.