What is an allergy?
Allergies are very common and affect about one in three New Zealanders at some time in their lives. There are many different causes of allergy, and symptoms range from very mild to potentially life threatening. Allergy is one of the major factors associated with the cause of and persistence of asthma.
An allergy occurs when a person’s immune system over-reacts to substances — called an allergen — in the environment. These allergens are found in house dust mites, pets, pollen, foods, drugs, insect stings, latex and moulds. An allergen for one person may not be a problem for another person, and everyone reacts differently.
What happens when you have an allergic reaction?
Antibodies are supposed to protect our bodies against viruses, parasites and infections. But for people with an allergy, their immune system mistakenly identifies the particular allergen as an invader and begins to create antibodies against it. These antibodies, called IgE, attach themselves to mast cells, which are abundant under the surface of the skin and in the nose, eyes, lungs and gastrointestinal tract. When the allergen is encountered, the IgE antibodies grab it, triggering the mast cells to release powerful chemicals, including histamine. This causes the allergic reaction. A reaction often occurs within minutes or up to a few hours after contact and may lead to many different symptoms.
What are the symptoms of an allergic reaction?
Symptoms of an allergic reaction may depend on where the allergen enters your body. An airborne allergen such as pollen, for example, is breathed in through the nose and usually causes symptoms in the nose, eyes, sinuses and throat, such as allergic rhinitis — commonly known as hay fever.
Food allergy, on the other hand, is more often associated with stomach or bowel problems and may cause hives. Allergic reactions can involve several parts of the body at the same time.
The symptoms of allergic reactions range from mild to severe to life threatening. They can be categorised according to the organs affected, which are:
• The skin: hives, eczema and facial swelling
• The respiratory system: symptoms can affect the nose (hay fever), throat (swelling) and lungs (cough, wheeze, bronchospasm)
• The gastrointestinal system: nausea, vomiting, stomach pains and diarrhea
• The cardiovascular system: feeling faint, weakness, pallor, floppiness (particularly in infants), and collapse.
Allergic symptoms may only occur locally — for example localised swelling to a bee sting — or they can be generalised (widespread).
An anaphylactic reaction is where a generalised allergic reaction affects the respiratory and/or cardiovascular systems, as well as the skin and/or gastrointestinal tract.
What are common allergens?
The most common causes of allergic reactions in New Zealand are:
• dust mites
Airborne triggers are commonly dust mites, pollen, mould spores, and cat and dog allergens. Skin contact or inhalation of an airborne allergen can lead to symptoms of skin rash, swelling of the eyes, hay fever and asthma. Airborne allergens are not often a trigger for anaphylaxis.
Food allergens are most often ingested. Any type of food can trigger and allergic reaction. The majority of allergic reactions are triggered by egg, cow’s milk (dairy), peanuts, tree nuts (eg cashews, almond, Brazil nuts), soy, wheat, seeds, fish and shellfish.
• Egg and dairy are the most common triggers in infants.
Food may trigger reactions that range from localised contact reactions through to generalised reactions, including anaphylaxis.
Insect venom is an injected allergen from stinging insects such as bees and wasps. The venom from each of these insects is different, and being allergic to one doesn’t mean you will be allergic to others. Reactions range from local reactions, which can be large and last for a number of days, to immediate generalised reactions, including anaphylaxis. Because a sting punctures the skin, anaphylaxis can be rapid.
Honey bees leave a venom sac behind. To avoid any further injection of honey bee venom, it’s recommended to flick this sac off immediately and not to pinch it to remove it.
Medication, including natural and herbal products, may trigger an allergic reaction. Antibiotics, usually penicillin, are the most commonly reported trigger. Medication may trigger an allergic reaction at any age.
Other triggers include allergy to latex in rubber products, and exercise can also be a cause of anaphylaxis.
It’s important to note that allergic reactions to food, insect venom and medication may be more severe in people who have asthma compared with those who don’t have asthma.
Who is allergic?Specific allergies are not inherited, for example allergy to pollen or peanuts, but the tendency to be allergic is. The potentially allergic infant is one who has one or more allergic parents, grandparents or siblings. The reasons for developing allergies are not entirely known, but any person may develop an allergy at any age.
The best way to prevent symptoms is to avoid what triggers the allergy. The allergic person needs to become very aware of when symptoms develop and take steps to reduce contact with the offending substances. Identifying allergens is not simple and may require skilled intervention or help. Click here to find out about how allergies are diagnosed.
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Source: Some of this information has been adapted from the Australasian Society of Clinical Immunology