What are allergies characterized by?

Allergies are characterized as abnormal reactions to harmless substances, which is encapsulated in the correct choice. In a typical allergic response, the immune system mistakenly identifies a substance that is usually harmless—such as pollen, dust mites, certain foods, or animal dander—as a threat. This causes the body to produce an immune response that can result in inflammation, itching, sneezing, and other symptoms associated with allergies.

This hypersensitivity is a hallmark of allergic reactions, distinguishing them from normal immune responses which are protective against genuinely harmful pathogens. The misunderstanding of harmless substances as threats explains the discomfort and various reactions many people experience during allergy seasons or in response to certain foods or environments.

Other options do not accurately capture the nature of allergies: normal reactions to harmful substances would refer to an appropriate response to pathogens, genetic disorders pertain to inherited conditions rather than immune responses, and common colds are caused by viruses and not by immune responses to harmless environmental allergens.