Final answer:
Allergic reactions occur when the immune system has an exaggerated response to harmless substances known as allergens, resulting in symptoms like itchy eyes and sneezing. The immediate immune response categorized as Type I Hypersensitivity is responsible for such overreactions to environmental substances.
Step-by-step explanation:
When people overreact to the usual things in their environments, it is most commonly due to allergic reactions. Allergies occur when the immune system overreacts to a substance in the environment that is typically harmless to most people. These substances, known as allergens, can be anything from pollen, dust mites, and mold to specific foods such as peanuts and certain medications.
Type I Hypersensitivities encompass such allergic responses, where exposure to an allergen triggers an immediate immune response. Symptoms of allergies can include itchy eyes, watery eyes, swollen tissues, sneezing, and in severe cases, anaphylaxis. Therefore, the correct answer to the question is B. Allergic reactions.