A food allergy is an adverse immune response to a food protein. They are distinct from other adverse responses to food, such as food intolerance, pharmacological reactions, and toxin-mediated reactions.
During an allergic reaction to food, irritant chemicals (such as histamine) are released into the tissues. This can result in itchy rashes, stomach upset, cough and wheeze and the more severe symptoms of anaphylaxis. These reactions are due to allergy, which is an immune system reaction to foods. When people complain of symptoms such as headaches, bloating or mouth ulcers after eating, they are describing food intolerance, rather than food allergy.
The protein in the food is the most common allergic component. These kinds of allergies occur when the body’s immune system mistakenly identifies a protein as harmful. Some proteins or fragments of proteins are resistant to digestion and those that are not broken down in the digestive process are tagged by the Immunoglobulin E (IgE). These tags fool the immune system into thinking that the protein is harmful. The immune system, thinking the organism (the individual) is under attack, triggers an allergic reaction. These reactions can range from mild to severe. Allergic responses include dermatitis, gastrointestinal and respiratory distress, including such life-threatening anaphylactic responses as biphasic anaphylaxis and vasodilation; these require immediate emergency intervention. Individuals with protein allergies commonly avoid contact with the problematic protein. Some medications may prevent, minimize or treat protein allergy reactions. As of now there is no cure.
Nearly a quarter of adults think food allergy or intolerance sufferers as just ‘fussy’ eaters, yet 45% of the British population are living with a food intolerance and 2% with a food allergy.
In light of Food Allergy & Intolerance Week, we’ve got the lowdown on what it means to have a food allergy, how it’s diagnosed and what treatment is available.Causes
Normally, your body’s immune system defends against potentially harmful substances, such as bacteria, viruses, and toxins. In some people, an immune response is triggered by a substance that is generally harmless, such as a specific food. The cause of food allergies is related to your body making a type of allergy-producing substance called immunoglobulin E (IgE) antibodies to a particular food.
Although many people have a food intolerance , food allergies are less common. In a true food allergy, the immune system produces antibodies and histamine in response to the specific food . Any food can cause an allergic reaction, but a few foods are the main culprits. In children, the most common food allergies are to:
Shellfish (shrimp, crab, lobster)
A food allergy frequently starts in childhood, but it can begin at any age. Fortunately, many children will outgrow their allergy to milk, egg, wheat, and soy by the time they are 5 years old if they avoid the offending foods when they are young. Allergies to peanuts, tree nuts, and shellfish tend to be lifelong.
In older children and adults, the most common food allergies are:
Food additives — such as dyes, thickeners, and preservatives – may rarely cause an allergic or intolerance reaction.
An allergy syndrome that affects the mouth and tongue may occur after eating certain fresh fruits and vegetables. These foods contain substances similar to certain pollens. For example, melon contains substances similar to ragweed pollen, and apples have allergens similar to tree pollen.
Many Americans believe they have food allergies, while in reality fewer than 1% have true allergies. Most symptoms are caused by intolerances to foods such as:
Cow’s milk and dairy products (See: Lactose intolerance)
Wheat and other gluten-containing grains (See: Celiac disease).
These allergic reactions have an acute onset (from seconds to one hour) and may include:
Itching of mouth, lips, tongue, throat, eyes, skin, or other areas
Swelling (angioedema) of lips, tongue, eyelids, or the whole face
Runny or congested nose
Wheezing and/or shortness of breath
Abdominal pain and/or stomach cramps
Symptoms of allergies vary from person to person. The amount of food needed to trigger a reaction also varies from person to person.
Symptoms of allergic diseases can certainly give strong hints that a person is indeed suffering from allergies. However, in most cases, various tests are required to confirm a diagnosis. Testing depends on the type of allergic disease in question.
Symptoms usually begin immediately, within 2 hours after eating. Rarely, the symptoms may begin hours after eating the offending food.
If you develop symptoms shortly after eating a specific food, you may have a food allergy. Key symptoms include hives, hoarse voice, and wheezing.
Other symptoms that may occur include:
Itching of the mouth, throat, eyes, skin, or any area
Lightheadedness or fainting
Patches of itchy, scaly skin (atopic dermatitis); skin may peel or blister
Swelling (angioedema), especially of the eyelids, face, lips, and tongue
Shortness of breath
Symptoms of mouth (oral) allergy syndrome:
Itchy lips, tongue, and throat
Swollen lips (sometimes)
Once a diagnosis is made (e.g. migraines, hives, eczema, irritable bowel, recurrent mouth ulcers), the history may help identify the role of dietary or other factors in making symptoms worse. The only reliable way to determine if diet is playing a role is by people being placed on a temporary elimination diet under the supervision of a dietitian and medical practitioner. If the diet helps, this is followed by challenges under controlled conditions to identify dietary triggers so that they can be avoided in the future.
It is important to emphasise that elimination diets must only be undertaken for a short term, under strict medical supervision and only for very good reasons. Prolonged restricted diets can lead to problems with nutrition, particularly in children.
In severe reactions, you may have low blood pressure and blocked airways. Blood or skin tests are sometimes used to confirm that you have an allergy. However, there is no well-accepted criteria for diagnosing food allergies. With elimination diets, you avoid the suspected food until your symptoms disappear. Then the foods are reintroduced to see if you develop an allergic reaction.
In provocation (challenge) testing, you eat a small amount of the suspected food allergen under medical supervision. This type of test may provoke severe allergic reactions. Challenge testing should only be done by a doctor.
Never try to deliberately cause a reaction or reintroduce a food on your own. These tests should only be performed under the guidance of a health care provider — especially if your first reaction was severe.
There are three common types of allergy testing: skin prick test, blood test, and food challenges. An allergist can perform these tests, and they can also go into further depth depending on the results.Prick Tests: Skin testing on arm is a common way for detecting an allergy, however, it is not as effective as other tests. For skin prick tests, a tiny board with protruding needles is used. The allergens are placed either on the board or directly on the skin. The board is then placed on the skin, in order to puncture the skin and for the allergens to enter the body. If a hive appears, the person will be considered positive for the allergy. This test only works for IgE antibodies. Allergic reactions caused by other antibodies cannot be detected through skin prick tests. RAST Tests: Blood testing is another way to test for allergies; however, it poses the same disadvantage and only detects IgE allergens and does not work for every possible allergen. RAST, RadioAllergoSorbent Test, is used to detect IgE antibodies present to a certain allergen. The score taken from the RAST test is compared to predictive values, taken from a specific type of RAST test. If the score is higher than the predictive values, there is a great chance the allergy is present in the person. One advantage of this test is that it can test many allergens at one time. Elimination Diet: Food challenges test for allergens other than those caused by IgE allergens. The allergen is given to the person in the form of a pill, so the person can ingest the allergen directly. The person is watched for signs and symptoms. The problem with food challenges is that they must be performed in the hospital under careful watch, due to the possibility of anaphylaxis.
The best method for diagnosing food allergy is to be assessed by an allergist. The allergist will review the patient’s history and the symptoms or reactions that have been noted after food ingestion. If the allergist feels the symptoms or reactions are consistent with food allergy, he/she will perform allergy tests.
“We would urge those who are experiencing symptoms of a food allergy to visit their GP and ask for a referral to an allergy consultant in a specialist allergy clinic,” says McManus Allergy UK.
The mainstay of treatment for food allergy is avoidance of the foods that have been identified as allergens. For people who are extremely sensitive, this may involve the total avoidance of any exposure with the allergen, including touching or inhaling the problematic food as well as touching any surfaces that may have come into contact with it. If the food is accidentally ingested and a systemic reaction (anaphylaxis) occurs, then epinephrine should be used. It is possible that a second dose of epinephrine may be required for severe reactions. There are treatments for an allergic reaction. Among the first time the reaction occurs, it is most beneficial to take the person to the emergency room, where proper action may be taken. Other treatments include: epinephrine, antihistamines, and steroids.
The only proven treatment for a food allergy is to avoid the food. Other treatments, including allergy shots and probiotics, have not been clearly proven to help with food allergies. If your child has a problem with cow’s milk formula, your health care provider may suggest trying a soy-based formula or something called an elemental formula, if available. If you suspect you or your child has a food allergy, consult an allergy specialist. If you have symptoms on only one area of the body (for example, a hive on the chin after eating the specific food), you may not need any treatment. The symptoms will likely go away in a brief time. Antihistamines may relieve the discomfort. Soothing skin creams may provide some relief.
Consult your doctor if you think you have had an allergic reaction to food, even if it is only a local reaction. Anyone diagnosed with a food allergy should carry (and know how to use) injectable epinephrine at all times. If you develop any type of serious or whole-body reaction (even hives) after eating the offending food, inject the epinephrine. Then go to the nearest hospital or emergency facility, preferably by ambulance. Seek immediate medical attention after injecting epinephrine for a food reaction.
The best treatment for food allergies is to avoid the food that causes the allergy. When that isn’t possible, you can use medicines such as antihistamines for mild reactions and the medicines in an allergy kit for serious reactions.
Start by telling your family, friends, and coworkers that you have a food allergy, and ask them to help you avoid the food. Read all food labels, and learn the other names that may be used for food allergens.
If your baby has a milk or soy allergy, your doctor may suggest either that you change the formula or that you feed your baby only breast milk. Specially prepared formulas are available for infants who have soy and milk allergies.
If you or your child has mild allergies, your doctor may suggest nonprescription antihistamines to control the symptoms. You may need prescription antihistamines if over-the-counter medicines don’t help or if they cause side effects, such as drowsiness.
If you have a severe allergic reaction, your first treatment may be done in an emergency room or by emergency personnel. You will be given a shot of epinephrine to stop the further release of histamine and to relax the muscles that help you breathe.
How to treat a reaction
If your doctor has prescribed an allergy kit, always keep it with you. It contains a syringe of epinephrine and antihistamine tablets. Your doctor or pharmacist will teach you how to give yourself a shot. Be sure to check the expiration dates on the medicines, and replace the medicines as needed.