Answer:
Allergens.
Step-by-step explanation:
Allergens are the substances that can enter in the body and causes the allergic reactions. The allergens are responsible for the hypersensitive reactions of the body.
The pollen, nuts and seafood acts as allergen for some individual. These substances causes the exaggerated immune response and allergic reactions in the sensitive individuals. The body generates an immune response against that allergen substances.
Thus, the answer is allergen.