Most common allergies are the result of

Most common allergies are the result of : type I (acute) hypersensitivity.

type I (acute) hypersensitivity refers to the negative reaction created by our body toward specific substances that called as an allergen.
In most cases, the body create the negative reaction because that person's body does not possess suitable autoimmune system to fight off the allergen.

productive most commonly means: achieving or producing a significant amount or result.

explanation:

productive can also mean:

producing or giving rise torelating to or engaged in the production of goods, crops, or other commodities.

these depend on how the word productive is used. most likely productive will mean   achieving or producing a significant amount or result.