That lead me to a bit of research, which lead me to Vicy Clarke’s Citric Acid Intolerance page.
The problem with having a citric acid intolerance is that citric acid is so hard to avoid, at least if you eat prepared foods.
Sounds familiar from avoiding gluten.
Citric acid is used as a flavoring, preservative and catalyst for other preservatives. And probably other uses as well.
Also, doing your own cooking makes it much easer to manage a citric acid intolerance. This may seem like a drag if you aren’t much of a cook, but the good news is that (a) this forces you towards a more healthy diet and (b) it really isn’t that hard to learn how to cook.
Vitamin B5 may help reduce reactions should you accidentally eat a citric acid containing food. This is confirmed.
These links are to a static website that appears unmaintained, although it has very useful information. Please let me know if the links stop working.