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 categorized 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 localized swelling to a bee sting — or they can be generalized (widespread).

An anaphylactic reaction is where a generalized 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
• pollen
• cats and other furry or hairy animals, such as dogs, horses, rabbits and guinea pigs
• food, such as peanuts, seafood, cow’s milk, egg and soy
• insect stings
• drugs
• mould
• latex

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 (e.g. cashews, almond, and Brazil nuts), soy, wheat, seeds, fish and shellfish.

• Egg and dairy are the most common triggers in infants.
• Peanuts, tree nuts and seafood are the most common triggers in older children, teenagers and adults.

Food may trigger reactions that range from localized contact reactions through to generalized 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 generalized 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 notes 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.

Source - http://www.foodallergy.org/questions.html

What is a food allergy?

A food allergy is an immune system response to a food that the body mistakenly believes is harmful. Once the immune system decides that a particular food is harmful, it creates specific antibodies to it. The next time the individual eats that food, the immune system releases massive amounts of chemicals, including histamine, in order to protect the body. These chemicals trigger a cascade of allergic symptoms that can affect the respiratory system, gastrointestinal tract, skin, or cardiovascular system. Scientists estimate that approximately 12 million Americans suffer from true food allergies.

FAAN's "Do You Have a Food Allergy?" brochure, distributed at health fairs throughout the country, is available thanks to a grant from the American College of Allergy, Asthma & Immunology (ACAAI). Download a copy (.pdf ~ 30kb).

What are the common symptoms of a reaction?

Symptoms range from a tingling sensation in the mouth, swelling of the tongue and the throat, difficulty breathing, hives, vomiting, abdominal cramps, diarrhea, drop in blood pressure, and loss of consciousness to death. Symptoms typically appear within minutes to two hours after the person has eaten the food to which he or she is allergic.

What is the best treatment for food allergy?

Strict avoidance of the allergy-causing food is the only way to avoid a reaction. Reading ingredient labels for all foods is the key to maintaining control over the allergy. If a product doesn't have a label, allergic individuals should not eat that food. If a label contains unfamiliar terms, shoppers must call the manufacturer and ask for a definition or avoid eating that food.

Is there a cure for food allergies?

Currently, there are no medications that cure food allergies. Strict avoidance is the only way to prevent a reaction. Most people outgrow their food allergies, although peanuts, nuts, fish, and shellfish are often considered lifelong allergies. Some research is being done in this area and it looks promising. Click here for research information.

Should I stop eating the food that I think I'm allergic to?

Randomly taking food out of your diet can leave you with an unbalanced diet that can cause other health problems. Additionally, you may become frustrated because you reach a point where you believe that everything you eat is causing a reaction. Seek the help of a doctor before making significant changes in your diet.

What is the best treatment for a food allergy reaction?

Epinephrine, also called "adrenaline," is the medication of choice for controlling a severe reaction. It is available by prescription as a self-injectable device (EpiPen® or Twinject®).

What is the difference between food allergy and food intolerance?

Many people think the terms food allergy and food intolerance mean the same thing; however, they do not. “Food intolerance" is an adverse food-induced reaction that does not involve the immune system. Lactose intolerance is one example of food intolerance. A person with lactose intolerance lacks an enzyme that is needed to digest milk sugar. When the person eats milk products, symptoms such as gas, bloating, and abdominal pain may occur.

A "food allergy" occurs when the immune system reacts to a certain food. The most common form of an immune system reaction occurs when the body creates immunoglobulin E (IgE) antibodies to the food. When these IgE antibodies react with the food, histamine and other chemicals (called "mediators") cause hives, asthma, or other symptoms of an allergic reaction.

What information should I provide my doctor?

Keep a food diary, for 1 to 2 weeks, of everything you eat, what symptoms you experience, and how long after eating they occur. This information, combined with a physical examination and lab tests, will help the doctor determine what, if any, food is causing your symptoms.

What is the difference between a prick skin test and a blood test or RAST test?

The prick skin test or a blood test, such as the RAST (or radioallergosorbent test), is commonly used to begin to determine if an allergy exists. The RAST can sometimes be called the CAP-RAST or ImmunoCap test.

A prick skin test is usually cheaper and can be done in the doctor's office. The doctor places a drop of the substance being tested on the patients' forearm or back and pricks the skin with a needle, allowing a tiny amount to enter the skin. If the patient is allergic to the substance, a wheal (mosquito bite-like bump) will form at the site within about 15 minutes.

A RAST test requires a blood sample. The sample is sent to a medical laboratory where tests are done with specific foods to determine whether the patient has IgE antibodies to that food. The results are usually received within one week.

Which test is better?

Although both tests are reliable, there are instances where one is better than the other. Many doctors use a RAST for young children or patients who have eczema or other skin problems that would make if difficult to read the results of a prick skin test. The results of either test are combined with other information, such as a history of symptoms and a food challenge, to determine whether a food allergy exists. Learn more about Food Allergy Testing (.pdf ~40KB)

How is food allergy related to eosinophilic esophagitis?

Eosinophilic esophagitis (EE) is a disorder characterized by the infiltration of a large number of eosinophils, a type of white blood cell, in the esophagus (the tube connecting the mouth to the stomach). EE can be triggered by food allergies. Once a diagnosis of EE is confirmed, allergy testing is typically requested. In many situations, avoiding ‘allergens’ that trigger the eosinophils will be an effective treatment. Skin allergy testing will include skin prick testing and may also include patch testing (to look for delayed reactions.) To learn more about EE, please visit the American Partnership for Eosinophilic Disorders Web site at www.apfed.org .