The most common types of allergic reactions are caused by things like food allergies, plant and pollen allergies, mosquito bites, and bee stings. An allergy-inducing agent can cause a mild to severe response involving the gastrointestinal tract, eyes, nose, skin, or respiratory tract. Reaction time can be within seconds, or in the case of a delayed reaction, it can take several hours. Most often an allergic reaction will present in less than one hour.
All types of allergic reactions are caused by the hypersensitivity of the immune system to an allergen. Any item, chemical, or substance that causes an allergic reaction is an allergen. There are four different categories of hypersensitivity, although some medical professionals include a fifth type.
Hypersensitivity is classed by how an allergen provokes a response from the immune system. The most common is Type 1, which is also called the immediate or anaphylactic type. Type 1 hypersensitivity includes common allergic reactions such as seasonal allergies, reactions to insect bites or stings, and food and drug allergies.
Allergic reactions can be mild to life-threateningly severe. The most serious of the Type 1 allergic reactions is called anaphylaxis, which can occur within seconds of exposure to an allergen. Anaphylaxis produces a systemic bodily reaction and requires immediate medical treatment. There's no single allergen that will always produce a severe response; the occurrence of anaphylaxis depends entirely upon the individual's immune reaction to any given allergen.
Contact allergies are caused by allergens that come in contact with the eyes, skin, or hair. This type of allergy usually produces, redness, itching, and inflammation at the contact site, but can spread to other areas. Eye allergies can produce eye swelling, itching, redness, and blurry vision, and can be mistaken for a contagious eye infection called pink eye. Food allergies often cause diarrhea, flatulence, abdominal discomfort, hives, or rashes. Hay fever, or allergic rhinitis, is a very common allergy and is triggered by plant pollens, molds, animals dander, and dust mites.
The milder types of allergic reactions include hives, mild congestion, watery or itchy eyes, an itchy or runny nose, and mild congestion. The more serious types of allergic reactions include trouble breathing or swallowing, dizziness, fainting, severe diarrhea, rapid pulse, and abdominal pain. Mild allergic reactions can be treated at home, but the more severe types of allergic reactions require prompt treatment from a medical professional.