I was on a long flight from Newark to Zürich on United Airlines. I have a severe tree nut allergy and was therefore allowed to pre-board the plane. When I got on the plane, I notified a flight attendant of my allergy and asked if she could try to make sure that the people sitting around me did not eat any nuts for the duration of the flight. The flight attendant told me that she would do her best but could not tell people what they could not eat. She also said that she would check the food being passed out to see if there was nuts in anything.
She came back after checking and said that they were not serving any food with nuts for this flight. I got settled into my seat and she approached me again and told me there were a few empty seats and asked if I wanted to switch to a seat in that area so there would be less people around. I switched seats to the more empty area. A few hours into the flight the flight attendants started handing out dessert. They gave me a cookie and I assumed there were no nuts in it because the flight attendant told me there was no nuts in any of the food being served, but luckily I thought to check for myself. When I read the nutrition label, it said contains almonds and may contain other tree nuts. I flagged down a flight attendant and told her to take back the cookie, as I was allergic, but I felt that I could not do anything about the people around me eating nuts as they had already started eating their cookies, which could have put me in danger.