DD1 has multiple severe allergies and has had since birth. She vomited all the time and we realised, once she was diagnosed, that she had been reacting to what I was eating as she got it through my breast milk. We knew she couldn't tolerate formula milk from day 4 and later discovered it contained beta carotene, to make it a more attractive colour(!). She has now, at 27, been diagnosed a severely coeliac and is struggling to get free from food she can eat, as a lot of them contain things she is allergic to already.
Eating out was a nightmare when she was a child. For DB's wedding, I went to the hotel and explained what she could have and when her meal arrived, some 'helpful' waitress had dumped a load of salad on her plate which contained vast amounts of grated carrot. I was less than pleased and told her to remove it and cook another chicken breast, as that one was contaminated. Twice the waitress tried to fob me off with the same chicken, but tiny bits of carrot had stuck to it. I finally went into the kitchen and the chef (who was a friend) went ballistic, as he had explained about 60 times to all the kitchen staff about the allergies and kept DD's food separate. She finally got her main course when we were all on our desserts.
She has a genuine penicillin allergy, but that didn't stop a know-it-all GP prescribing it for her, as 'there is no such thing'. I had the joy, when she was in her mid-teens, of taking her to Boots and explaining that if she wanted to have sex, she would have to carry the non-latex condoms, as her boyfriends would only have the latex ones. She would also have to ask what her boyfriends had eaten before kissing them. When she became pregnant, they were not sure if she would be allergic to her baby or not. She wasn't, but did not tolerate pregnancy well and lost over 7 kilos and any subsequent pregnancies will have to be micro-managed.
People who claim to have allergies and don't should be taken out and shot at dawn.