An allergic reaction to certain types of natural, unprocessed foods, such as peanuts, is caused by:
(1) a lack of digestive enzymes
(2) a response to specific antigens
(3) microorganisms living within the food
(4) high levels of carbon dioxide in the air

option 1) a lack of digestive enzymes

Explanation:

An allergic reaction involves a disorderly response of the body to certain substance(s). A good example is lactose intolerance (Inability to fully metabolize lactose) in adult humans to milk.

Usually, allergic reaction is based on lack of digestive enzymes to certain types of natural, unprocessed foods, such as peanuts

as resources become scarce because of population growth, the growth decreases after few years due to lack of resources and food.