It seems that an awful lot of people have allergies, including asthma and nobody knows why, all sorts of theories abound why.
50 + yrs ago I do not remember widespread allergies, antibiotics were probably used on a larger scale then both for humans and animals whereas they are tightly controlled now. So why we are getting more allergies remains a mystery, there is much less air pollution, I remember when city air was much worse than now and water pollution much worse, the environment is much cleaner now.
It is all tied up with the immune system, either it is not developing or it is being damaged by some event, or illness.
Food is very unlikely to be a cause of allergies, how do you identify any particular cause when there is no such thing as pure food, even what you grow in your garden. Everything has some kind of contaminant, soil, bacteria, fungus, air, water, and all the additives in processed food, we all rely on our immune systems to protect us.