Here is my take
1.)the use of anti-biotics has exploded in recent years altering the bodies bowel flora which leads to a leaky-gut
type condition and predisposes the person to be more prone to allergies.(not to mention all the anti-bacterial soaps currently being used which have a similar affect)
2.) repetitive eating is more common,repetitive eating exposes your immune system to one type of food over and over again and is a leading cause of allergies.
3.)CHEMICAL BURDEN environmental toxins,such as pesticides,some people are allergic to the pesticides used to grow the peanuts rather then the peanuts themselves,also the use of chemicals decreases the immune system.
4.)lack of breast feeding and bottle fed babies get twice the amount of food allergies,and also babies ex posed to certain foods such as peanuts way to early causes allergies later in life.
5.)Certain foods do not agree with people biologically or genetically for example most Chinese people are lactose intolerant because milk cows were not raised in China and milk was not part of their ancestral diet,so they lack the lactase enzyme to break it down.