What is an allergic reaction?

An allergic reaction is the response of the immune system to a foreign substance that enters the body. 

An allergic reaction is an overreaction of the immune system to a substance called an allergen. Allergens include chemicals, foods, medicines, mold, plants, and pollen.

Symptoms of an allergic reaction can range from mild and annoying to severe and life-threatening.

• Allergens can affect different tissues in the body, such as the airways, eyes, gastrointestinal tract, nose, lungs, and skin.
• Some allergic reactions, such as hives or itching around an insect bite or where a plant or chemical touched the skin, affect only one area of the body.
• Other allergic reactions may affect the whole body, causing itching, swelling, or difficulty breathing.
• A severe allergic reaction (called anaphylaxis) can lead to shock and even death.

Allergic reactions do not occur the first time a person is exposed to an allergen. A person may become more sensitive to the allergen with each exposure.

Allergic reactions are sensitivities to a specific substance, called an allergen, which is contacted through the skin, inhaled into the lungs, swallowed, or injected. They are fairly common; approximately 50 million Americans suffer from some form of allergic disease, and the incidence is increasing.

Some allergic reactions may be mild enough to treat at home while others are severe and life-threatening. First time exposure to a potential allergen may only produce a mild reaction, but once a person is sensitized, repeated exposure may lead to more severe reactions.

An allergic reaction may be a side effect of drugs, certain foods or drinks, various chemicals or environmental factors, which involves immunologic mechanisms (the immune system's distinction of self from nonself). Common allergens may include: plants, pollens, animal danders, bee stings, insect bites, medications, nuts and shellfish.

Certain agents are most often responsible for allergic reactions in surgical patients. These include neuromuscular blocking agents, latex, colloids, hypnotics, antibiotics, benzodiazepines (anti-anxiety agents), opioids (often used to treat pain or for sleep induction), local anesthetics, intravenous (IV) contrast media (a diagnostic tool), and blood products. The antibiotics most commonly associated with allergic reactions are the sulfonamides, penicillins, and cephalosporins.

Anaphylaxis is the most severe form of allergic reaction. It can present as an acute, life-threatening reaction with multiple organ system involvement or it can be more localized in appearance. Approximately 1 in every 2,700 hospitalized patients experience drug-induced anaphylaxis. If antibodies are not involved in the process, the reaction is termed anaphylactoid. However, it is not possible to distinguish between anaphylactic and anaphylactoid reactions through clinical observation.

You should read product labels, and discuss all therapies with a qualified healthcare provider. Natural Standard information does not constitute medical advice, diagnosis, or treatment.

The mechanism of an allergic reaction is essentially the normal immune system reacting as it would when confronted with a harmful microbe. But rather than a pathogen sounding the alarm bell, a harmless allergen triggers an unnecessary immune response. The resulting inflammatory response goes into high gear for way too long, which can damage surrounding tissues. The problem is made worse because once learned, or sensitized, the same response kicks in every time the immune system encounters the harmless allergen. And it takes only minuscule amounts of the allergen to set a full-blown allergic reaction in motion.

Although allergies vary in terms of which allergen causes the reaction and where in the body the reaction takes place, most allergic reactions involve immunoglobulin E (IgE) antibodies, the products of plasma cells, descendants of the immune system's activated B cells. In people with allergies, IgE is stimulated upon first exposure to an allergen such as pollen or bee venom. The IgE antibodies bind to a type of immune cell called a mast cell. The mast cells, now armed with IgE antibodies, roam the body, ready to trigger an allergic response the next time the same allergen appears. Mast cells act like guard dogs at the gates, ready not just to sound the alarm but also to swing into attack mode by instigating the body's inflammatory response.

Allergic reaction starts when the mast cells release certain chemical mediators, such as histamines and other agents. These mediators are instrumental in causing the telltale symptoms of an immediate allergic reaction -- swollen and inflamed tissue, sneezing, coughing, wheezing, runny eyes, itchiness, and so on. And once it's revved up, the reaction keeps on going, with more inflammatory cells massing at the site, releasing more powerful chemicals, such as leukotrienes, which cause yet more inflammation. A prolonged inflammatory response can damage tissues, such as those in the airways, and can lead to debilitating chronic diseases such as asthma.

An allergic reaction is a hypersensitivity disorder in which the person's immune system strongly reacts against a normally harmless substance from the environment to produce an inflammatory response. An allergic reaction is activation of white blood cells called mast cells in the blood and tissues that overreact to produce proteins and immunoglobulin E, ultimately initiating the inflammatory response. Essentially your body is activating and fighting against whatever allergic substance or allergen you came in contact with, producing symptoms such as hay fever, red eyes, itchy and runny nose, eczema, hives, or even an asthma attack.