Food alergy

Symptoms

For some people, an allergic reaction to a particular food may be uncomfortable but not severe. For other people, an allergic food reaction can be frightening and even life-threatening. Food allergy symptoms usually develop within a few minutes to an hour after eating the offending food.

The most common food allergy symptoms include:

• Tingling in the mouth
• Hives, itching or eczema
• Swelling of the lips, face, tongue and throat, or other parts of the body
• Wheezing, nasal congestion or trouble breathing
• Abdominal pain, diarrhea, nausea or vomiting
• Dizziness, lightheadedness or fainting

Anaphylaxis

In some people, a food allergy can trigger a severe allergic reaction called anaphylaxis. This can cause life-threatening symptoms, including:

• Constriction and tightening of airways
• A swollen throat or a lump in your throat that makes it difficult to breathe
• Shock, with a severe drop in blood pressure
• Rapid pulse
• Dizziness, lightheadedness or loss of consciousness

Emergency treatment is critical for anaphylaxis. Untreated, anaphylaxis can cause a coma or death.

Exercise-induced food allergy

Some people have an allergic reaction to a food triggered by exercise. As the body is stimulated by exercise, a person with an exercise-induced food allergy may feel itchy and lightheaded. In serious cases, it can cause reactions such as hives or anaphylaxis. Not eating for a couple of hours before exercising and avoiding certain foods may help prevent this problem.

Pollen-food allergy syndrome

In many people who have hay fever, fresh fruits and vegetables and certain nuts and spices can trigger an allergic reaction that causes the mouth to tingle or itch. In some people, pollen-food allergy syndrome — sometimes called oral allergy syndrome — can cause swelling of the throat or even anaphylaxis. This is an example of cross-reactivity. Proteins in fruits and vegetables cause the reaction because they're similar to those allergy-causing proteins found in certain pollens. For example, if you're allergic to ragweed, you may also react to melons; if you're allergic to birch pollen, you may also react to apples. Cooking fruits and vegetables can help you avoid this reaction. Most cooked fruits and vegetables generally don't cause cross-reactive oral allergy symptoms.

Causes

In a true food allergy, your immune system mistakenly identifies a specific food or a substance in food as a harmful substance. Your immune system triggers cells to release antibodies known as immunoglobulin E (IgE) antibodies to fight the culprit food or food substance (the allergen). The next time you eat even the smallest amount of that food, the IgE antibodies sense it and signal your immune system to release a chemical called histamine, as well as other chemicals, into your bloodstream.

These chemicals cause a range of allergic signs and symptoms. They are responsible for causing allergic responses that include dripping nose, itchy eyes, dry throat, rashes and hives, nausea, diarrhea, labored breathing, and even anaphylactic shock.

The majority of food allergies are triggered by certain proteins in:

• Shellfish, such as shrimp, lobster and crab
• Peanuts
• Tree nuts, such as walnuts and pecans
• Fish
• Eggs

In children, food allergies are also commonly triggered by proteins in:

• Eggs
• Milk
• Peanuts
• Tree nuts

Chocolate, long thought by some parents to cause food allergies in children, rarely triggers a food allergy.

Food intolerance and other reactions

There are a number of reactions to food that cause similar symptoms to a food allergy. If you have digestive symptoms, chances are it's not a true food allergy, but a food intolerance. Depending on the type of food intolerance you have, you may be able to eat small amounts of problem foods without a reaction. By contrast, if you have a true food allergy, even a tiny amount of food may trigger an allergic reaction. Because a food intolerance may involve some of the same signs and symptoms as a food allergy does — such as nausea, vomiting, cramping and diarrhea — people often confuse the two.

One of the tricky aspects of diagnosing food intolerance is that some people are sensitive not to the food itself but to a substance or ingredient used in the preparation of the food.

Common conditions that can cause symptoms mistaken for a food allergy include:

• Absence of an enzyme needed to fully digest a food. You may not have adequate amounts of some enzymes needed to digest certain foods. Insufficient quantities of the enzyme lactase, for example, reduces your ability to digest lactose, the main sugar in milk products. Lactose intolerance can cause bloating, cramping, diarrhea and excess gas.
• Irritable bowel syndrome. Certain foods may trigger the signs and symptoms of irritable bowel syndrome. You may find that certain foods will cause cramping, constipation or diarrhea. Steer clear of these foods to avoid the symptoms.
• Food poisoning. Sometimes food poisoning can mimic an allergic reaction. Some types of mushrooms and rhubarb can be toxic. Bacteria in spoiled tuna and other fish also can make a toxin that triggers harmful reactions.
• Sensitivity to food additives. Some people have digestive reactions and other symptoms after eating certain food additives. For example, sulfites used to preserve dried fruit, canned goods and wine can trigger asthma attacks in sensitive people. Other food additives that could trigger bad reactions include monosodium glutamate (MSG), artificial sweeteners and food colorings.
• Recurring stress or psychological factors. Sometimes the mere thought of a food may make you sick. The reason is not fully understood.
• Celiac disease. While celiac disease is sometimes referred to as a gluten allergy, it isn't a true food allergy. Like a food allergy, it does involve an immune system response, but it's a unique immune system reaction that's more complex than a simple food allergy. This chronic digestive condition is triggered by eating gluten, a protein found in bread, pasta, cookies, and many other foods containing wheat, barley or rye. If you have celiac disease and eat foods containing gluten, an immune reaction occurs that causes damage to the surface of your small intestine and an inability to absorb certain nutrients. Symptoms of celiac disease include diarrhea, abdominal pain and bloating. In some cases, celiac disease causes malnutrition and nutrient deficiencies. 

Risk factors

Food allergy risk factors include:

• Family history. You're at increased risk of food allergies if asthma, eczema, hives or allergies, such as hay fever, are common in your family.
• A past food allergy. Children may outgrow a food allergy, but in some cases it returns later in life.
• Other allergies. If you're already allergic to one food, you may be at increased risk of becoming allergic to another. Likewise, having another type of allergy, such as hay fever, increases your risk of having a food allergy.
• Age. Food allergies are most common in children, especially toddlers and infants. As you grow older, your digestive system matures and your body is less likely to absorb food or food components that trigger allergies. Fortunately, children typically outgrow allergies to milk, soy, wheat and eggs. Severe allergies and allergies to nuts and shellfish are more likely to be lifelong. 

Complications

Complications of food allergy can include:

• Anaphylaxis, a life-threatening allergic reaction.
• Atopic dermatitis (eczema). About one in three people with atopic dermatitis also have a food allergy.
• Migraines. Histamines, released by your immune system during an allergic reaction, have been shown to trigger migraines in some people.

While some people think food allergies are linked to childhood hyperactivity and to arthritis, there's no evidence to support this.

Diagnosis

The following may help determine if you have a true food allergy, rather than a food intolerance, food poisoning or some other condition.

• Description of your symptoms. Be prepared to tell your doctor a history of your symptoms — which foods, and how much, seem to cause problems — and whether you have a family history of food allergies or other allergies.
• Food diary. Your doctor may ask you to keep a food diary of your eating habits, symptoms and medications to pinpoint the problem.
• Elimination diet. You may be asked to eliminate suspect foods for a week or two, and then add the food items back into your diet one at a time. This process can help link symptoms to specific foods. However, this isn't a foolproof method. Psychological factors as well as physical factors can come into play. For example, if you think you're sensitive to a food, a response could be triggered that may not be a true allergic one. If you've had a severe reaction to foods, this method can't be safely used.
• Physical examination. A careful exam can identify or exclude other medical problems.
• Skin test. A skin prick test can determine your reaction to particular foods. In this test, small amounts of suspected foods are placed on the skin of your forearm or back. Your skin is then pricked with a needle, to allow a tiny amount of the substance beneath your skin surface. If you're allergic to a particular substance being tested, you develop a raised bump or reaction.
• Blood test. A blood test can measure your immune system's response to particular foods by checking the amount of allergy-type antibodies in your bloodstream, known as immunoglobulin E (IgE) antibodies. For this test, a blood sample taken in your doctor's office is sent to a medical laboratory, where different foods can be tested. However, these blood tests aren't always accurate.

Treatments and drugs

The only way to avoid an allergic reaction is to avoid the foods that cause signs and symptoms. However, despite your best efforts, you may come into contact with a food that causes a reaction.

For a minor allergic reaction, over-the-counter or prescribed antihistamines may help reduce symptoms. These drugs can be taken after exposure to an allergy-causing food to help relieve itching or hives. However, antihistamines can't treat a severe allergic reaction.

For a severe allergic reaction, you may need an emergency injection of epinephrine and a trip to the emergency room. Many people with allergies carry an autoinjector (Anapen). This device is a combined syringe and concealed needle that injects a single dose of medication when pressed against your thigh. If your doctor has prescribed an epinephrine autoinjector:

• Carry it with you at all times. It may be a good idea to keep an extra autoinjector in your car or in your desk at work as well.
• Always be sure to replace epinephrine before its expiration date, or it may not work properly.
• Be sure you know how to use the autoinjector. Also, make sure the people closest to you know how to administer the drug — if they're with you in an anaphylactic emergency, they could save your life.

While there's ongoing research to find better treatments to reduce food allergy symptoms and prevent allergy attacks, there isn't any proven treatment that can prevent or completely relieve symptoms. Unfortunately allergy shots (immunotherapy), a series of injections used to reduce the effect of other allergies such as hay fever, aren't effective for treating food allergies.

The key treatment is to do your best to avoid the food in question, and work with your doctor to identify what steps you can take to relieve your symptoms and how to spot and respond to a severe reaction.

Lifestyle remedies

One of the keys to preventing an allergic reaction is to completely avoid the food that causes your symptoms.

• Don't assume. Always read labels on manufactured foods to make sure they don't contain an ingredient you're allergic to. Even if you think you know what's in a food, check the label. Ingredients sometimes change. Food labels are required to clearly list whether they contain any common food allergens. Read food labels carefully to avoid these top eight sources of food allergens: milk, eggs, peanuts, tree nuts, fish, shellfish, soy and wheat.
• When in doubt, say no thanks. At restaurants and social gatherings, you're always taking a risk that you might eat a food you're allergic to. Many people don't understand the seriousness of an allergic food reaction and may not realize that a tiny amount of a food can cause a severe reaction in some people. If you have any suspicion at all that a food may contain something you're allergic to, steer clear.
• Involve caregivers. If your child has a food allergy, enlist the help of relatives, baby sitters, teachers and other caregivers. Make sure they understand how important it is for your child to avoid the allergy-causing food and that they know what to do in an emergency.

Alternative medicine

Research on alternative food allergy treatments is limited. However, many people do try them and claim that certain treatments help.

• Herbal remedies. A few small studies of herbal remedies have showed some benefit in reducing symptoms and preventing anaphylaxis, including some Chinese medicine formulas. However, there's no reliable proof yet these work. In addition, there are concerns about the quality of some herbal preparations from China. If you do take an herbal remedy, be sure to tell your doctor about it. It may affect test results or interact with other medications you take.
• Acupuncture and acupressure. There's little academic research on acupuncture for food allergies, and the studies that do exist don't show a clear benefit from these techniques. However, many of people claim that these treatments help with a number of health conditions, including allergies, and there's little risk in trying them, providing you work with an experienced and certified provider.
• Special diets. In the past, "rotating diets" that have you avoid certain foods at certain times were tried as a food allergy treatment. There's no evidence that this or other such diets are an effective food allergy treatment. The only food strategy proved to work is complete avoidance of the allergy-causing food.

Coping and support

A food allergy can be challenging and a source of ongoing concern. Having a good source of information and the opportunity to discuss the condition with others who share your concerns can be very helpful. A number of Internet sites and nonprofit organizations offer information and forums for discussing food allergies. Some are specifically for parents of children with food allergies.

Prevention

The best way to prevent an allergic reaction is to know and avoid foods that cause signs and symptoms. For some people, this is a mere inconvenience, but others find it a greater hardship. Also some foods — when used as ingredients in certain dishes — may be well hidden. This is especially true in restaurants and in other social settings.

If you know you have a food allergy, follow these steps:

• Know what you're eating and drinking. Be sure to read food labels carefully.
• If you have already had a severe reaction, wear a medical alert bracelet or necklace that lets others know that you have a food allergy in case you have a reaction and you're unable to communicate.
• Talk with your doctor about prescribing emergency epinephrine (adrenaline).
• If you have asthma, be sure to ask if sulfites have been added to foods when dining in restaurants. When shopping for foods, check labels for the terms "sodium bisulfite," "potassium bisulfite," "sodium sulfite," "sulfur dioxide" and "potassium metabisulfite.
• When eating out, be sure your server is aware that you absolutely can't eat the food you're allergic to, and you need to be 100 percent certain that the meal you order doesn't contain it. Also, be aware of cross-contamination of food in the kitchen — make sure food isn't prepared on surfaces or in pans that contained any of the food you're allergic to. It's better yet if you talk with the chef — don't be reluctant to make your needs known. Restaurant staff are usually more than happy to help when they clearly understand your request.

If your child has a food allergy, take these precautions to ensure his or her safety:

• Notify key people that your child has a food allergy. Talk with child care providers, school personnel, parents of your child's friends, and other adults who regularly interact with your child. Emphasize that an allergic reaction can be life-threatening and requires immediate action. Make sure that your child also knows to ask for help right away if he or she reacts to food.
• Explain food allergy symptoms. Teach the adults who spend time with your child how to recognize signs and symptoms of an allergic reaction.
• Write an action plan. Your plan should describe how to care for your child when he or she has an allergic reaction to food. Provide a copy of the plan to your child's school nurse and others who care for and supervise your child.
• Have your child wear a medical alert bracelet or necklace. This alert lists your child's allergy symptoms and explains how others can provide first aid in an emergency.

References:

http://allergy-ireland.ie/food-allergy/

https://en.wikipedia.org/wiki/Food_allergy

http://acaai.org/allergies/types/food-allergies

http://www.safefood.eu/Food-safety/Food-Allergies/Allergy-or-intolerance.aspx

https://www.fsai.ie/legislation/food_legislation/food_information/14_allergens.html