I'm allergic to milk. All dairy in anything no matter how little or what had been done to it, but I can tolerate the 'made in the same factory as'. It is only consumption of, not exposure to thankfully.
The result is that our home is dairy free and that most things are cooked from scratch. There is a lot of label reading when we are out. Even things I knew were fine have to be checked it there is the slightest changed in the label, from new packaging to that awful phrase 'new recipe'! My husband is dairy free which has helped his snoring issue and guests east dairy free as well. If they really need milk in their coffee or tea, I have some long life milk sachets which I expect will go bad before they are all used!
Eating out is getting easier than it used to be. I can usually eat at vegetarian restaurants without much issue. One of the larger pizza chains now has a dairy free option for each course and one of the oriental chains has several main meals that are fine. Otherwise I have to ring up and talk with the Chef that is on that day and arrange with them what I am having in advance.
But as a rule, I don't eat out much because of the worry, buy I know by the 2nd bite if there is going to be a problem!