- An allergy is an abnormal sensitivity or reaction of your immune system to a substance (an allergen) that you eat, inhale or touch. Non-allergic people can usually tolerate this substance.
- Nearly 50% of all people who suffer from allergies have hay fever.
- If both parents have allergies, their children are more likely to develop an allergy, although not always the same kind of allergy.
- Almost 70% of adults with food allergies are younger than 30 years and most children are under three years old.
The function of the immune system is to protect the body against foreign substances or hostile invaders such as viruses, bacteria and harmful chemicals. When such a substance enters the body, the immune system reacts by producing proteins called antibodies or by sending specific white blood cells called eosinophils to that area.
Eosinophils attack infection, viruses, bacteria and other foreign substances. It is also these white blood cells that cause the immune system to overreact while they “attack” an invader, which usually is a substance harmless to other people.
Antibodies against harmful substances are produced by beta-lymphocytes, the body’s white blood cells that are responsible for fighting infections. Antibodies attach themselves to the substances and set off a reaction that destroys them. Antibodies usually leave harmless substances alone.
The immune system produces five kinds of antibodies, each with its own function. Allergic reactions involve the IgE antibody. Allergic persons form IgE antibodies against substances that are harmless in most individuals, such as certain types of food and pollen, called antigens or allergens. Once the IgE antibodies are formed against a specific allergen, they bind to certain mast cells and basophils which circulate in the blood. This process is called allergic sensitisation.
When a person is exposed to that specific allergen again, the IgE antigens attached to mast cells and basophils bind to the allergen, causing a reaction that makes the mast cell burst. When the mast cell bursts (also called degranulation of mast cells), it releases chemicals such as histamine. These chemicals make the blood vessels dilate and smooth muscles contract. For example, the smooth muscles of the bronchi contract and the air passage narrows, which may lead to asthma. These chemicals also attract eosinophils to that area. The eosinophils release chemicals that neutralise the chemicals released by the mast cells.
When the allergic reaction is severe, so much histamine is released that the person’s blood pressure drops, blood circulation slows down and the bronchi contract, causing respiratory distress. Such a severe allergic reaction is called anaphylactic shock and may cause death. Fortunately this is rare.
Cause and symptoms
The cause of most people’s allergies is not known. However, an allergy usually begins with sensitisation when the person is exposed to an allergen. This period may last from several days to a few decades. The repeated exposure to an allergen triggers the immune system to form the antibodies that cause the allergic reaction to the specific antigen.
Allergies are classified according to the substances causing them or the parts of the body they affect.
Allergic rhinitis (nasal allergy or allergies of the nose)
Breathing air that contains an allergen causes allergic rhinitis, the most common respiratory allergy. It often begins around the age of two years, but the most common age when this allergy to airborne substances begins is the late teens or early 20s. Allergic rhinitis is also sometimes called hay fever. Other respiratory allergies include those that affect the sinuses (allergic sinusitis), bronchial tubes (asthma) and lungs (hypersensitive pneumonitis).
Allergic rhinitis is usually seasonal. The most common allergens are pollens, grass or weed seeds spread by the wind. Hay fever is therefore a misleading name, since it is not caused by hay (it also does not produce fever). Perennial allergic rhinitis, which occurs all year round, is usually a reaction to indoor allergens such as moulds, dust and dust mites, as well as animal dander. Dander is the flakes of dried animal skin, saliva and urine that cause an allergic reaction. Sometimes it is wrongly assumed that people who are allergic to pets are allergic to their fur or hair.
Symptoms of allergic rhinitis are worse when the specific allergen is present and may grow worse over a number of years. Sometimes symptoms lessen slightly with age. The symptoms of allergic rhinitis include:
- Continuous sneezing, especially after waking up in the morning
- Runny nose and a postnasal drip
- Stuffy nose, which may be accompanied by frequent sniffing
- Watery eyes that are also itchy
- Itchy ears, nose and throat
- Continuous rubbing of nose (in children)
- “Allergic shiners” â€“ dark circles under the eyes
- Discomfort in the facial area
- Tiredness or loss of energy
Rhinitis of pregnancy
Pregnant women sometimes have some of these symptoms without suffering from allergic rhinitis. This is called rhinitis of pregnancy. The cause is unknown, although hormones released during pregnancy may be the cause of swelling in the mucous lining of the nose. The higher circulating blood volume during pregnancy â€“ 40% above the levels of non-pregnant women â€“ may also congest the nasal passages.
The main causes of asthma, an abnormal reaction in the lower airways, are environmental exposure and allergies to allergens such as pollen, mould spores, animal dander and dust mites. Other allergies are linked to asthma, especially in children.
This skin allergy, characterised by itchy rashes, often occurs in children. It is caused by contact with a natural substance such as cat fur or a manufactured item such as soap that becomes an allergen.
Atopic dermatitis or eczema
Although it has no known cause, heredity is thought to play a role. Children who have a family history of allergies are prone to eczema, as are those who are allergic to milk, eggs, peanuts, soy, wheat or fish. Children who suffer from eczema are also more likely to develop other allergies later in life, such as allergic rhinitis or asthma. This syndrome is called atopy.
Eczema is characterised by an itchy red rash that usually starts on the cheeks but may also occur in the fold of the elbows, at the back of the knees and behind the ears. In its severe form it is characterised by “sheets” of thick, purple rash across the body. Scratching quickly spreads the rash and may lead to oozing and the forming of a crust.
Hives or urticaria
Lasting for minutes or days, hives (also called weals or welts) are large, itchy red bumps on the skin. Hives can also last for a longer period and are then referred to as chronic urticaria. These hives can be one or many bumps, and vary greatly in size and shape. Although they more commonly appear on the arms, legs and trunk, they can appear anywhere on the body as a result of the body’s reaction to factors such as certain foods, pollen, animal dander, drugs, insect bites, cold, heat, light or emotional stress. Histamine causes the hives to form.
Hives are generally not an emergency, but when they appear suddenly, spread rapidly and are accompanied by a swollen throat, tightness of the chest, wheezing or difficulty breathing, this indicates a severe allergic reaction that requires immediate medical attention.
More than 70% of people who have a food allergy are younger than 30 years. Adults account for only about one to two percent of people who are allergic to food or some substance in food. Although one in 12 children are suspected to have a food allergy, only one in 25 children are usually confirmed as having a food allergy.
Any food may cause an allergic reaction, but the prime causes are proteins in cow’s milk, egg white, peanuts, wheat and soybeans. Other less common causes include berries, shellfish, maize, beans, gum arabic, and the food colourant tartrazine, which is added to some green, orange and yellow foodstuffs. An allergic reaction to food usually occurs within half an hour of eating it, but can also occur within only five or 10 minutes or after four to six hours.
It is sometimes difficult to establish which allergens are responsible for a food allergy, because reactions to certain foods are sometimes delayed or they may be caused by food additives or eating habits. A food allergy causes a variety of symptoms in the skin, digestive tract and respiratory system. Anaphylactic shock can result in severe cases. Symptoms of a food allergy are:
- Stomach cramps
- Swelling of the face and tongue, and respiratory congestion (severe cases)
The most common allergy in this category is a reaction to drugs in the penicillin family. Other drugs that can trigger allergic reactions include:
- Local anaesthetics
- Dyes injected into blood for X-ray purposes
Insect sting allergies
It is thought that people who have allergies such as food, drug or respiratory allergies are more prone to insect sting allergies. The venom in the stings of bees, wasps, hornets, yellow jackets and fire ants is the common allergen triggering this type of allergic reaction.
If people know they have an allergy to insect stings and that they can easily come into contact with the venom, it is best for them to carry a single-dose injection kit of adrenaline. Injecting themselves with the adrenaline will help counteract and alleviate allergic symptoms until they can receive medical attention.
Allergies occur across the age, sex and race spectrum. An allergy can start at any age. Children are most vulnerable to allergies, especially allergic rhinitis. Boys younger than 10 years are twice as likely as girls in this age group to have symptoms of allergies to airborne substances.
Of the five different classes of antibodies that the immune system produces, those belonging to the IgE class are formed in reaction to allergens. These antibodies bind with the allergen and attach to two types of defensive cells, namely the mast cells and basophils. The cells in turn produce mediators (the best known being histamine), which are responsible for the symptoms of an allergic reaction such as sneezing, runny nose and itching.
As soon as the cells have produced these mediators, “reinforcements” in the form of eosinophils, a type of white blood cell, are attracted to the area where the reaction is taking place, producing an even more intense reaction.
If left untreated, allergic rhinitis in children may lead to complications such as regular ear infections, which may in turn influence speech development in young children. It is important to note that there is no indication that children actually outgrow the tendency to be allergic. They may outgrow a specific allergy but develop another one. Allergic reactions tend to subside with age, but adults seldom “outgrow” allergies.
- Upper respiratory infections
Heredity â€“ if one parent is allergic, a child runs a risk of 30 to 50% of inheriting the tendency to be allergic, although he or she may not necessarily develop the parent’s particular type of allergy. If both parents have allergies, their children have a 60 to 80% likelihood of developing allergies. Only 25 to 50% of identical twins share the same type of allergy.
Environment â€“ although heredity determines whether you will have an allergy of some sort, it is usually the environment that sets the process in motion. The environmental factor has an influence when you are in a place where you are exposed to high levels of a specific antigen, especially early in life.
Upper respiratory infections â€“ children who contract viral or bacterial infections of the upper respiratory system (nose, throat and bronchial tubes) before they are six months old are more likely to develop allergies or conditions such as asthma later on in life.
Although emotional stress may trigger an allergy, allergies do not have a psychosomatic origin.
When to see a doctor
Always consult a health professional when you have the following symptoms:
- Violent stomach cramps, vomiting, bloating or diarrhoea â€“ you could have food poisoning, a serious allergic reaction to food or another kind of allergic reaction.
- Painful or difficult breathing â€“ get medical treatment immediately. You could be having an asthma attack, another serious allergic reaction or a heart attack.
- Sudden development of hives, accompanied by severe flushing and itching, and rapid heartbeat â€“ you need urgent medical attention, as these symptoms could indicate the onset of anaphylactic shock
- Pain in the sinus area, fever and a yellow or green discharge from the nose â€“ you may have a sinus infection
- A cough or cold that does not subside within a week or two
- Swelling of the face around the eyes and lips
Also consult your doctor if non-prescription allergy medicines do not relieve your allergy symptoms, or if the symptoms suddenly get worse for no apparent reason.
As a number of conditions resemble allergies but do not involve the immune system, it is not always easy to diagnose an allergy. In the case of a mild allergy, tests may not be necessary and your general practitioner or family doctor can base his or her diagnosis on your medical history and a thorough physical examination.
However, certain laboratory tests are suggested when the allergy is severe. A clinical immunologist usually performs these tests.The following laboratory tests may be done to verify the cause of an allergy:
- Complete blood cell count â€“ although not always routinely used for allergy testing, this blood test is performed to detect an increase in the eosinophil white blood cell count. If the test results show a higher than normal number of these white blood cells, it is an indication that the body is trying to fight off a foreign invader such as an allergen. (A high count of eosinophil white blood cells is also found in people with Churg-Strauss syndrome.)
- Nasal smear â€“ a sample of mucus obtained from the nose is examined for an increase in eosinophil white blood cells.
- Radio-allergosorbent (Rast) test â€“ the amount of IgE antibodies in the bloodstream is measured in serum that recognises allergens inhaled by the patient. It is therefore also a reliable test for inhalant and food allergens. If the test results show a high amount of IgE antibodies against a certain allergen, it is highly probable that the person has an allergy to that allergen.
- Skin test â€“ if it is not clear from someone’s medical history what he/she is allergic to, a skin prick test may be done. In this test, a solution of a suspected allergen is injected into the skin to determine whether there is IgE immunologic hypersensitivity. If the person is allergic, a small hive and redness around the hive (flare) will appear within 15 to 20 minutes on the skin area where the test was done. This test yields the best results when testing for inhalant allergies, insect sting allergies and drug allergies. It can also help to determine whether you have food allergies.
These tests are not completely reliable; if too much of the substance is injected, it may cause a reaction in a non-allergic person. In addition, extremely sensitive people may go into anaphylactic shock when even just a tiny amount of the substance is injected into their skin.
If the doctor’s prescribed treatment does not alleviate your symptoms or the doctor suspects you may have another problem, more advanced tests may be necessary. These include X-rays or a CAT scan of the sinuses to detect sinusitis or structural nose defects. A nasal endoscopy, which enables the surgeon to look inside the nose passages with a lighted, flexible tube, may be done to look for structural defects, infections or Nasal polyps.
There is no cure for allergies. The best way to control or treat any allergy is to avoid the triggering substance. However, this may be difficult. The most common treatments are:
- Antihistamine â€“ blocking the release of histamine by the body’s mast cells in body tissue (histamine causes the allergic reaction).
- Decongestants â€“ shrinking swollen nasal tissues, thereby relieving congestion. These drugs are sometimes combined with an antihistamine and control nasal symptoms effectively.
- Steroids â€“ controlling inflammation and stopping allergic reactions. At the same time, these anti-inflammatory substances reduce nasal swelling and mucous secretions.
- Topical creams or skin ointments â€“ for eczema
- Immunotherapy or allergy injections â€“ can gradually build tolerance to the allergenic substance so that the body no longer reacts to it.
- Antibiotics â€“ may also be necessary to treat complications such as the ear and sinus infections that are common in children with allergies.
There is a wide range of medicines for treating asthma. Usually more than one type of medication is prescribed, firstly to relieve the symptoms during an acute attack and secondly to control the symptoms over time.
If you have had a severe allergic reaction in the past, you should always carry a kit to treat anaphylactic shock and give yourself an injection from the kit when necessary. It is important to get medical treatment immediately, but while waiting for medical help to arrive, lie down with your legs raised above chest level to increase the blood flow to your heart and brain.
People with asthma are likely to suffer from complications during and after surgery. Make sure your doctor knows that you have asthma, as you will probably need to have a number of tests done before undergoing surgery.
You should also inform your doctor if you suffer from allergic rhinitis and it is not possible to schedule the operation outside the “hay fever” season.
No nutritional or herbal treatments or vitamin or mineral supplements have been proven to be successful in treating allergies. If you are allergic to pollen, you should be especially careful of herbal remedies, as they may contain the very substances that activate your allergic symptoms!
Unless you are allergic to some food substance, you do not have to change your diet to prevent an allergic reaction. As an allergy is not caused by a nutritional deficiency but is a reaction of the immune system, taking vitamin and mineral supplements will not help to prevent an allergic reaction.
Depending on your specific allergies, some preventive maintenance at home could help control the environment, thereby reducing the risk of allergic reactions. These steps include:
- Using special mattress and pillow covers to control dust mites
- Frequent vacuuming and dusting to get rid of dust mites and other airborne allergens
- Using an air conditioner in your home and car and changing the filters often
- Getting rid of old bedding, toys, clothing and other items that may be carriers of dust and mould
- Keeping pets outdoors as much as possible and off the furniture
- Bathing pets regularly to reduce dander
- Mopping uncarpeted surfaces regularly
- Removing overstuffed furniture and carpets to reduce dust mites
Revision date: June 22, 2011
Last revised: by Jorge P. Ribeiro, MD
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