Food allergy occurs in about 6% to 8% of children.
The majority of food allergic reactions occur in the first years of a
child’s life. As children grow older, they loose their sensitivity
to milk and eggs, but not to peanuts, fish, tree nuts, and shellfish.
For a child with a food allergy, eating even a tiny amount
of a particular food can cause symptoms such as nausea, skin rash,
vomiting, diarrhea, and cramping. A severe allergic reaction can
cause swelling in the throat or mouth, wheezing, a sudden drop
in blood pressure, and severe difficulty breathing. This kind of
severe reaction is called anaphylaxis. Food allergies are the leading
cause of anaphylaxis. Food related anaphylaxis causes 200 deaths
per year in the United States.
WHAT IS FOOD ALLERGY?
Food allergy is an immunologic reaction which results from
eating a particular food or food additive. Food allergy occurs
when the body’s immune system reacts to certain proteins in a
particular food.
Food allergy is a reaction that usually involves the IgE
(immunoglobulin E) mechanism.
WHAT FOODS ARE ASSOCIATED WITH ALLERGIES?
Only a few foods account for 90% of allergic reactions in children.
These foods include: peanuts, milk, eggs, wheat, tree nuts, fish,
and shellfish.
Allergies to peanuts and tree nuts account for most fatal
anaphylactic reactions.
WHAT TYPES OF FOOD ALLERGIES ARE THERE?
Basically, there are IgE-mediated food allergies, non-IgE-mediated
food allergies, and mixed allergies.
(1) IgE-mediated allergies involve the Type I immune mechanism.
Examples follow.
Oral allergy syndrome (IgE):
Commonly associated with eating fresh fruits and vegetables.
Symptoms: itching of the mouth, swelling (angioedema) of the
tongue, lips, and throat.
Immediate gastrointestinal hypersensitivity (IgE):
Often associated with atopic disease, with signs of allergy
in other organs.
Symptoms: abdominal pain, nausea, diarrhea, and vomiting.
(2) Non-IgE-mediated allergies involve the Type II immune mechanism.
Examples follow.
Dietary protein enterocolitis (Non-IgE):
Protein intolerance in infants – especially to cow’s milk.
Symptoms: recurrent vomiting and diarrhea.
Celiac disease (Non-IgE):
Malabsorption illness, with sensitivity to wheat, rye, and barley.
Symptoms: abdominal pain and chronic diarrhea.
Most adverse food reactions are actually cases of food intolerance.
In fact, only 6% to 8% of children have a true food allergy. Food
intolerance is an abnormal physiologic response to a food or food
additive. Food intolerance is the result of non-immunologic mechanisms.
Food intolerance can be caused by a number of problems, including:
Anatomical problems, metabolic reactions, pharmacologic
reactions, toxic reactions, psychological reactions, infectious reactions,
celiac disease, digestive problems, and reactions to preservatives.
Examples of the various causes of food intolerance follow.
Metabolic reactions: lactase deficiency, favism, pancreatic insufficiency, galactosemia, and phenylketonuria.
Approximately 2% of infants experience an adverse reaction to milk.
Forty percent of the time, the problem is caused by the body’s
deficiency of the ß-lactase enzyme, a problem also known as
lactose intolerance. Lactose intolerance is not an allergic reaction,
however, but a metabolic problem. The symptoms are:
flatulence, abdominal cramps, and diarrhea.
Pharmacologic reactions: histamine, caffeine, tyramine in cheese,
theobromine in chocolate, alcohol, and serotonin in tomatoes.
Flavorings and preservatives: monosodium glutamate, and sodium metabisulfate.
Toxic reactions: dyes, seafood toxins, bacterial toxins,
fungal toxins, pesticides, and heavy metal contaminants.
Infectious reactions: Salmonella, Giardia, and hepatitis.
Digestive problems: celiac disease is an enteropathy which
leads to malabsorption of food.
WHAT IS THE MECHANISM OF ALLERGIC REACTION AND ANAPHYLAXIS?
Foods are composed of carbohydrates, proteins, and lipids.
The major food allergens are primarily the water-soluble glycoproteins.
In children, the foods responsible for most of the allergic reactions are:
milk, peanuts, eggs, soybeans, fish, tree nuts, and wheat.
The body’s immune system can overreact to food proteins,
called allergens. An antibody called immunoglobulin E is involved.
An IgE-mediated allergic reaction to food is the result of
interactions involving antigen-presenting cells (APCs), T cells,
and B cells.
An antigen (usually a glycoprotein) interacts with an
antigen-presenting cell.
Later, T cells are activated, and this causes B lymphocytes
to produce IgE antibodies to the antigen.
The IgE antibodies bind to the IgE receptors of mast cells,
macrophages, basophils, and eosinophils.
When the offending food is eaten again, the food antigen
eventually binds to the complementary IgE on the surface of
basophils, mast cells, eosinophils, and macrophages. At this point,
when the IgE antibody meets the offending food antigen, chemicals
are released that act on the throat, airway, skin, heart, and intestines.
These chemicals are: histamine, leukotrines, prostaglandins, and cytokines.
These are the molecules which are responsible for both mild and
severe allergic reactions.
WHAT ARE THE SIGNS AND SYMPTOMS OF FOOD ALLERGY?
A child with a food allergy can have symptoms beginning as
soon as 2 minutes after eating the food, or as long as 1 to 2 hours
afterwards.
Signs and symptoms of IgE-mediated food allergy can range
from very mild symptoms (oral allergy syndrome) to a severe, life-threatening anaphylactic reaction. A variety of skin, gastrointestinal, respiratory,
and generalized symptoms are associated with IgE-mediated food allergy.
Examples of food allergy symptoms follow.
Skin:
Acute urticaria (itching wheals) and angioedema (painful swelling)
are the most common skin manifestations of food hypersensitivity reactions.
The causes in children are usually: milk, peanuts, eggs, and tree nuts.
Oral allergy syndrome:
Localized swelling of the lips, tongue, palate, and throat.
Temporary lingual papillitis (strawberry tongue). These symptoms
are usually well-controlled with an antihistamine, such as Benadryl.
The causes in children are usually: ingestion of a variety of
fruits and vegetables.
Gastrointestinal anaphylaxis:
Abdominal pain, nausea, abdominal cramping, diarrhea, and vomiting.
Generalized anaphylaxis reaction:
Systemic anaphylaxis is the most severe form of food allergy,
and is potentially life-threatening.
The early symptoms of food-induced anaphylaxis often include:
tingling in the throat, oral itching and tingling, shortness of breath,
great difficulty breathing, tightness in the chest, nausea, abdominal pain,
vomiting, swelling of the face, hives, and passing out.
Symptoms usually start within 30 minutes after food ingestion,
and rarely 2 hours after ingestion.
Symptoms can sometimes be controlled with prompt intramuscular
administration of adrenaline (epinephrine).
WHAT ARE THE STEPS IN DIAGNOSING A FOOD ALLERGY?
A careful medical history and physical examination of the
child are the most important initial steps in diagnosing a food allergy.
A systematic review of the diet is next:
Patients are often asked to keep a diet diary, which records:
foods eaten, description of symptoms experienced, and the time
between ingestion of food and appearance of symptoms.
Allergy skin prick tests:
Using glycerinated food extracts, a positive control (histamine),
and a negative control (saline), a physician can screen for food allergy.
Unfortunately, the positive predictive accuracy of skin prick
tests is only 50%. A negative test result, however, confirms the
absence of an IgE-mediated reaction, and is 95% accurate in excluding
a particular IgE-mediated food allergen.
RAST:
Serologic radioallergosorbent test is a blood test which checks
for IgE antibodies against a specific food allergen.
A 1-2-week elimination diet of all foods which are suspected by
the medical history , skin prick tests, or other tests.
Finally, the double-blind, placebo-controlled food challenge
is the “gold standard” for the diagnosis of a food allergy.
WHEN TO GO TO THE HOSPITAL:
An anaphylactic reaction can be life-threatening. Any food
reaction that causes shortness of breath, a feeling of choking,
dizziness, or passing out requires immediate evaluation and
treatment in a medical emergency department.
If a child has shortness of breath, dizziness, tightness in
the chest – then emergency treatment needs to be started.
The hospital treatment will include: adrenaline injection,
oxygen administration, steroid administration, and other medications
to relieve the symptoms.
EMERGENCY MEDICAL TREATMENT FOR SEVERE ALLERGIC REACTION:
Around 200 people die each year in the United States because
of food-related allergic reactions. What follows are the medical steps
needed manage anphylaxis.
1) Assess the severity of the allergic reaction.
2) Monitor the patient. Assess the airway, breathing, and circulation.
3) Administer supplemental oxygen by mask, and keep the airway open.
4) Treat severe systemic symptoms with an intramuscular
injection of epinephrine 1:1,000 at 0.01 ml/kg. This can be
repeated every 15 minutes, as needed.
5) Administer intravenous fluids to ensure tissue perfusion –
30 ml/kg of crystalloid.
6) Treat bronchospasm with albuterol 0.5% at 2 puffs, from a
metered-dose inhaler.
7) Administer an oral or intramuscular antihistamine (Benadryl)
at 1 mg/kg, up to a maximum of 75 mg.
8) Administer a systemic corticosteroid such as methylprednisolone,
at 2 mg/kg.
9) Treat severe reactions with intubation and other advanced
lifesaving techniques, as needed.
WHAT IS THE LONG-TERM TREATMENT FOR FOOD ALLERGY?
Treatment of food allergy consists of: teaching the patient and
family how to avoid the offending food. The family is also taught
how to recognize and manage the symptoms of an allergic reaction.
For management of oral lesions caused by a mild food allergy,
the palliative treatment consists of swabbing a 1:1 mixture of a
Benadryl and Kaopectate on the tongue, lips, and inside of the mouth.
HOW CAN FOOD ALLERGY BE PREVENTED?
The only sure way to prevent food allergies is to avoid eating
the foods which cause the problem.
In restaurants, parents need to ask what ingredients are in the
food being ordered.
Parents need to carefully read the ingredients on food labels.
A physician will provide the parent with a self-injectable
device (Epi-Pen Jr.) which contains epinephrine for use in a
pediatric emergency. Parents should receive instructions for using this device before leaving the doctor’s office.
Children who are a risk for anaphylaxis should wear a medical
alert ID bracelet. This bracelet can alert teachers and medical
personnel about the risk for an allergic reaction.
It is now known that food ingested by a mother can be passed on
to the unborn baby via the uterus, or to the infant via breast milk.
Mothers in high-risk families should consider eliminating peanuts
and tree nuts from their diet during pregnancy and during breastfeeding.
An article in Contemporary Pediatric provides
a practical guide to the diagnosis of food hypersensitivity reactions.
It distinguishes between food allergy and food intolerance. The
article describes various IgE-mediated and
non-IgE-mediated food reactions. An overview of the diagnostic
approach to food allergies is also presented.
