I cannot remember where I found this, but when you eat something that you might be sensitive to in the evening the reaction is 10 times worse than if you ate that same food earlier in the day.

I have a 8 YO GD, that has a lot of food issues that we could never pin down, this information helped us, because if she ate oranges early in the day she might not have a reaction but if she ate an orange in the evening, she would break out in hives by the next day. (& yes, she should be GF but is not, hence the worsening food issues. & she just got over a case of walking pneumonia)