What is an allergy? How are immune cells involved in allergic reactions?

An allergy is a hypersensitive reaction of the immune system to typically harmless substances called allergens, such as pollen, animal dander, food, or insect bites. The primary immune cells involved in allergic reactions are mast cells, which contain histamine, and Immunoglobulin E (IgE) antibodies. When an individual encounters an allergen, their immune system produces IgE antibodies specific to that allergen, which bind to receptors on mast cells, sensitizing them. Upon subsequent exposure to the same allergen, the allergen binds to the IgE antibodies on mast cells, triggering the release of histamine and initiating an inflammatory response responsible for allergy symptoms, such as itching, swelling, and difficulty breathing.