Treatment for correction of peanut allergy has been successful, but requires a specialist's attention and treatment over a period of time.
Hard to tell why there seems to be an increase in recent years.

Many allergies are rare- I had an employee who was strongly impacted by oranges. Someone eating one in the next room would cause her to break out and prolonged exposure could be dangerous to her life. We were careful not to eat oranges or bring them into the building where she worked.
A professor of mine had severe allergic reactions to cucumbers. On field trips we had to avoid cafes where they were being used in salads, etc.- he could detect them from outside the cafe !
I have problems with vinegar and stay away from it. I can't eat yogurt that is not cooked without nausea, but the effects have not been serious.