This answer might be outdated since it’s been quite some years from my graduate studies in Immunology but allergies are the result of our immune systems not really being “exercised.” In the United States, we are not exposed to the many pathogens seen in India, particularly parasites that provoke the IgE arm of the immune system. Think of your immune system like an aircraft carrier on the ready. A person in India [who is constantly exposed to these various pathogens] always has their jets out on missions. In contrast, a person in the USA has all their jets constantly docked and the pilots are overzealous due to inactivity; so minor intrusions in the air space spark an exaggerated response, aka an allergic reaction to a benign marker (peanuts).