Allergies are the immune system’s incorrect response to allergens (foreign substances). Exposure to what is normally a harmless substance, for example pollen, causes the human immune system to react as if the substance is harmful. When people come into contact with an allergen, they may experience a number of allergic symptoms including itchy, watery nose and eyes (allergic rhinitis and allergic conjunctivitis); asthma symptoms such as wheezing and coughing; allergic eczema or hives (urticaria); and allergic shock (also called anaphylaxis or anaphylactic shock).
A hypersensitive response, or ‘allergic reaction’ is the result of how three factors interact with the body:
- The allergen – Allergens include pollen, mold, dust mites, certain foods, latex, insect bites or stings, and others.
- Mast cells – Although mast cells are found throughout the body, most reside in connective tissues such as those of the skin, tongue, the lining of the nose and intestinal tract, the lungs and upper airways.
- Immunoglobulin E (IgE) – IgE is an allergic antibody, a type of protein made by the immune system to recognize and fight specific body “invaders”. IgE coats the surface of the mast cells in tissues. The first time an allergy-prone person is exposed to an allergen (such as pollen), large amounts of the corresponding IgE antibodies (for example, pollen IgE antibodies) are produced.
The IgE antibodies cause the mast cells to release inflammatory chemicals that cause swelling of tissues, as well as histamine and several other chemicals that cause itching, engorgement of blood vessels, increased secretions and bronchospasm (tightening of muscles that surround the airways). Some of these chemicals attract white blood cells known as eosinophils. The eosinophils add more inflammatory chemicals. If the allergen is in the air, the allergic reaction will occur in the eyes, nose and lungs. If the allergen is ingested, the allergic reaction will occur in the mouth, stomach and intestines. Sometimes enough inflammatory chemicals are released to cause a reaction throughout the body, such as a severe rash, decreased blood pressure, shock or loss of consciousness. This severe type of reaction is called anaphylaxis and may be life-threatening.
Allergy symptoms can be categorized as mild, moderate or severe (anaphylactic). Mild reactions include local symptoms (affecting a specific area of the body) such as a rash or hives; itchy, watery eyes; and some congestion. Mild reactions do not spread to other parts of the body. Moderate reactions include symptoms that spread to other parts of the body. Symptoms may include itchiness that spreads or difficulty breathing. A severe allergic reaction, known as anaphylaxis, is a rare, life-threatening emergency in which the bodys response to the allergen is sudden and affects the whole body (systemic).
Common allergens that provoke allergic reactions in people include:
If you think you have allergies, don’t wait to see if your symptoms will go away. When your symptoms last longer than a week or two and tend to recur, make an appointment with your doctor so a complete medical evaluation can be performed.
Tests that may reveal the specific allergens include:
- Skin testing – the most common method of allergy testing. This may include intradermal, scratch, patch, or other tests. Skin testing may even be an option for young children and infants, depending on the circumstances.
- Blood test – also called RAST (radioallergosorbent), this measures the levels of allergy antibody, IgE, produced when your blood is mixed with a series of allergens in a laboratory. If you are allergic to a substance, the IgE levels may increase in the blood sample. The blood test may be used if you have existing skin problems like eczema, if you’re on medications that are long-acting or you cannot stop taking, if you have a history of anaphylaxis, or if you prefer not to have a skin test.
- ‘Use’ or ‘elimination’ tests – suspected items are eliminated and/or introduced while the person is observed for response to the substance. This is often used to check for food or medication allergies.
The goal is to reduce the symptoms caused by inflammation of the affected tissues.
- Short-acting antihistamines, which are generally non-prescription, often relieve mild to moderate symptoms but can cause drowsiness. In addition, these antihistamines can blunt learning in children (even in the absence of drowsiness).
- Longer-acting antihistamines cause less drowsiness and can be equally effective, and usually do not interfere with learning. These medications require a prescription.
- Nasal corticosteroid sprays are very effective and safe for people with symptoms not relieved by antihistamines alone. These are prescription medications also.
- Decongestants may also be helpful in reducing symptoms such as nasal congestion. Nasal spray decongestants should not be used for more than several days, because they can cause a ‘rebound’ effect and make the congestion worse. Decongestants in pill form do not cause this effect.
- Cromolyn sodium is available as a nasal spray for treating hay fever. Eye drop versions of cromolyn sodium and antihistamines are available for itchy, bloodshot eyes.
- Leukotriene inhibitors are a prescription medicine approved to help control asthma and to help relieve the symptoms of seasonal allergies. The most appropriate medication depends on the type and severity of symptoms. Specific illnesses that are caused by allergies (such as asthma, hay fever, and eczema) may require other treatments. Allergy shots (immunotherapy) are occasionally recommended if the allergen cannot be avoided and symptoms are hard to control. Regular injections of the allergen are given, with each dose slightly larger than the previous dose. Allergy shots keep your body from over-reacting to the allergen. They do not work for everybody and require frequent doctor’s visits.