An allergy is an abnormal reaction by a person's immune system against a normally harmless substance. A person without allergies would have no reaction to this substance, but when a person who is allergic encounters the trigger, the body reacts by releasing chemicals which cause allergy symptoms. However, just because there is a cause and effect between exposure to a substance and the development of symptoms does not always mean that a person is allergic to that substance.
For example, medications have known and expected side effects; a person experiencing one of these side effects is not necessarily allergic to that medication.
symptoms
Allergy is a local or systemic inflammatory response to allergens. Local symptoms are:
* Nose: swelling of the nasal mucosa (allergic rhinitis)
* Eyes: redness and itching of the conjunctiva (allergic conjunctivitis)
* Airways: Sneezing,bronchoconstriction, wheezing and dyspnoea, sometimes outright attacks of asthma, in severe cases the airway constricts due to swelling known as anaphylaxis.
* Ears: feeling of fullness, possibly pain, and impaired hearing due to the lack of eustachian tube drainage.
* Skin: various rashes, such as eczema, hives (urticaria) and contact dermatitis.
Systemic allergic response is also called anaphylaxis; multiple systems can be affected including the digestive system, the respiratory system, and the circulatory system. Depending of the rate of severity, it can cause cutaneous reactions, bronchoconstriction, edema, hypotension, coma and even death. This type of reaction can be triggered suddenly or the onset can be delayed.
The severity of this type of allergic response often requires injections of epinephrine, sometimes through a device known as the Epi-Pen auto-injector. The nature of anaphylaxis is such that the reaction can seemingly be subsiding, but may recur throughout a prolonged period of time.
Allergic rhinitis afflicts 20% of the US population. Also known as hayfever, symptoms can be in response to airborne pollen. Asthmatics are often allergic to dust mites. Apart from ambient allergens, allergic reactions can result from foods, insect stings and reactions to medications.
Diagnosis
Allergy testing measures how a person reacts to specific allergens, such as tree pollen, pet dander, foods, medications or molds. A "positive" allergy test means that a person has a specific allergic antibody to the substance tested. This often means that the person is allergic to the substance, meaning that the person will experience symptoms when exposed to the allergen.
However, a positive allergy test does not necessarily mean that the person is indeed allergic to the substance. A person may have a positive allergy test to dog dander, for example, but experience no symptoms with exposure to dogs. In addition, a person may have multiple positive food allergy tests, but be able to eat these foods without any bad reactions.
Therefore, an allergist is needed to perform and interpret allergy tests based on the person’s symptoms.
There are only two types of allergy testing considered to be valid: Skin testing (prick/puncture and intradermal) and RAST (radioallergosorbent test). Other tests for allergies may be performed in research settings (such as placing small amounts of allergen in the eye, nose or lungs to measure an allergic response), but are not helpful for everyday use. Patch testing is not used to test for allergy, but for contact dermatitis to various chemicals, which is due to another part of the immune system.
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