An allergic reaction is an over-response of the immune system to a particular substance or allergen (substances that cause an allergic reaction). Allergic reactions are common, and the severity of an allergic reaction can range from mild to severe to life-threatening. The most severe form of allergic reaction is an anaphylactic reaction. This type of allergic reaction is rare but rapidly becomes life-threatening and is a medical emergency.
There are a variety of types of allergies that cause allergic reactions. They include food allergies, respiratory allergies and skin allergies, which can result in such conditions as eczema and contact dermatitis.
In people who experience allergic reactions, the immune system is overzealous and reacts when they inhale, swallow or touch normally harmless substances, such as pollen or dust. The immune system is made up of special cells that circulate throughout the body to defend the body against foreign substances, such as viruses and bacteria. This over-reaction of the immune system during an allergic reaction results in the release of the chemical histamine. This causes the swelling, inflammation, and itching of tissues that are characteristic of an allergic reaction.
Almost any substance can cause an allergic reaction in a person who is sensitive to that particular substance. That substance is called an allergen. People who experience allergic reactions are often allergic to more than one substance. Common allergens include dust, pollen, mold spores, animal dander, bee stings, and cockroach or dust mite droppings. Other common allergic reactions occur in response to exposure to certain plants, such as poison ivy, and some medications, such aspirin or penicillin. Certain foods, such as eggs or milk, or chemicals and other substances, such as latex, are also common allergens that can cause an allergic reaction in a sensitive person.
When a person has an allergic reaction, exposure to an allergen can cause a wide variety of symptoms. Symptoms vary depending on the specific allergy, the type of exposure and the severity of the allergic reaction. Symptoms can affect the respiratory system, the skin and/or the gastrointestinal system. For more information on symptoms and complications, refer to symptoms of allergic reaction.
Making a diagnosis of an allergic reaction begins with performing a complete evaluation that includes a medical history, including symptoms, and a physical examination. Other tests may be done to rule out diseases or conditions with similar symptoms, such as an upper respiratory infection, sinusitis or other types of gastrointestinal diseases, such as irritable bowel syndrome.
Diagnostic testing may include skin patch testing. In a patch test, small amounts of common allergens are applied methodically to the skin to determine what substances are triggering an allergic reaction. A blood test called a radioallergosorbent test (RAST) may also be done to help identify the substance that is causing an allergic reaction. For suspected food allergies, a patient may also be asked to keep a food log to help determine the types of foods that trigger an allergic reaction.
It is possible that a diagnosis of an allergic reaction can be missed or delayed because symptoms can be similar to other conditions. For more information on misdiagnosis, refer to misdiagnosis of allergic reaction.
Patient compliance with a good treatment plan can control symptoms and repeat attacks of an allergic reaction to a degree that allows a person to live a normal, active life. Treatment may include a combination of lifestyle changes, medications, and other measures. For more information on treatment, refer to treatment of allergic reaction....more »