Having a hypersensitivity means that someone’s immune system has reacted to something in such a way that it ends up damaging them, as opposed to protecting them. There are four different types of hypersensitivities, and in the first type or type one, the reactions rely on Immunoglobulin E, or IgE antibody, which is a specific type of antibody - the other major ones being IgG, IgA, IgM, and IgD. So because IgE is involved with type one hypersensitivity reactions they are also called IgE-mediated hypersensitivities. This type of reaction is also sometimes called immediate hypersensitivities, because the reaction happens super fast on the order of minutes. So most allergic reactions are IgE-mediated, and therefore most allergies are type I hypersensitivity reactions. “Allergy” comes from the Greek Allos which roughly means “other” and ergon which means “reactivity”. Essentially, allergies are reactions to molecules from outside your own body that most people don’t react to and these are specific molecules from things you might breathe or take in like foods, animal dander, bee stings, mold, drugs or medications, and pollen.

You can also mount an allergic reaction to things you come in contact with on your skin like latex, lotions, and soaps. These specific molecules are also called antigens, and when they cause an allergic reaction, they’re called allergens. An allergic reaction happens in two steps, a first exposure, or sensitization, and then a subsequent exposure, which is when it gets a lot more serious. People that react to these allergens usually have a genetic predisposition to having over-reactions to unknown molecules or allergens. This means that these people have certain genes that cause their T-helper cells to be more hypersensitive to certain antigens. Since the production of these T-helper cells is genetically linked, allergies to things tend to run in families. So let’s say this person breathes in some ragweed pollen, that person happens to have T-helper cells that can bind to a specific molecule on the pollen, making that molecule an allergen. First off, that antigen gets picked up by immune cells hanging out in the membranes along the airways, which then grab the molecule and migrate to the lymph nodes, which happens regardless of if the person is allergic or not. These cells are antigen-presenting cells, since they carry the antigen to the lymph nodes and present it to the T-helper cells living there.

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