AP BIOLOGY

Detailed explanation-1: -Allergic reactions (hypersensitivity reactions) are inappropriate responses of the immune system to a normally harmless substance. Usually, allergies cause sneezing, watery and itchy eyes, a runny nose, itchy skin, and rash. Some allergic reactions, called anaphylactic reactions.

Detailed explanation-2: -An allergic reaction occurs when a person’s immune system becomes hypersensitive to certain substances, such as foods, pollen, medications, or bee venom. A substance that causes an allergic reaction is called an allergen. Many allergens are everyday substances that are harmless to most people.

Detailed explanation-3: -Hypersensitivity reactions are exaggerated or inappropriate immunologic responses occurring in response to an antigen or allergen. Type I, II and III hypersensitivity reactions are known as immediate hypersensitivity reactions because they occur within 24 hours of exposure to the antigen or allergen.

Detailed explanation-4: -Type I hypersensitivity is the most common type of hypersensitivity reaction. It is an allergic reaction provoked by re-exposure to a specific type of antigen, referred to as an allergen.