Question

what is an allergen?
the body fighting against itself
a foreign substance causing a reaction
the symptoms a person feels due to allergies

Explanation:

To determine the correct definition of an allergen, we analyze each option:

• "The body fighting against itself" describes an autoimmune response, not an allergen.
• "A foreign substance causing a reaction" matches the definition of an allergen, as allergens are external substances that trigger an allergic reaction in the body.
• "The symptoms a person feels due to allergies" refers to the manifestations of an allergic reaction, not the allergen itself.

Answer:

B. A foreign substance causing a reaction