Tips to Remember:
Up to two million, or 8%, of children in the
United States are estimated to be affected by food allergy, and up to 2% of
adults have food allergies.
With a true food allergy, an individual's
immune system will overreact to an ordinarily harmless food. This is caused
by an allergic antibody called IgE (Immunoglobulin E), which is found
in people with allergies. Food allergy often may appear in someone who has
family members with allergies, and symptoms may occur after that allergic
individual consumes even a tiny amount of the food.
Food intolerance is sometimes confused with
food allergy. Food intolerance refers to an abnormal response to a food or
food additive that is not an allergic reaction. It differs from an allergy
in that it does not involve the immune system. For instance, an individual
may have uncomfortable abdominal symptoms after consuming milk. This
reaction is most likely caused by a milk sugar (lactose) intolerance, in
which the individual lacks the enzymes to break down milk sugar for proper
digestion. Your allergist/immunologist can help you determine the difference
between intolerance and allergy and help you in establishing a management
Food allergens - those parts of foods that
cause allergic reactions - are usually proteins. Most of these allergens can
still cause reactions even after they are cooked or have undergone digestion
in the intestines. Numerous food proteins have been studied to establish
The most common food allergens - responsible
for up to 90% of all allergic reactions - are the proteins in cow's milk,
eggs, peanuts, wheat, soy, fish, shellfish and tree nuts.
All foods come from either a plant or an
animal source, and foods are grouped into families according to their
origin. Peanuts, black-eyed peas, kidney and lima beans, and soybeans are
some of the members of the legume family, whereas asparagus, chives, garlic
and onion are, surprisingly, members of the lily family.
In some food groups, especially tree nuts and
seafood, an allergy to one member of a food family may result in the person
being allergic to all the members of the same group. This is known as
cross-reactivity. However, some people may be allergic to both peanuts and
walnuts, which are from different food families; these allergies are called
coincidental allergies, because they are not related.
Within animal groups of foods,
cross-reactivity is not as common. For example, people allergic to cow's
milk can usually eat beef, and patients allergic to eggs can usually eat
With shellfish, crustaceans (shrimp, crab and
lobster) are most likely to cause an allergic reaction. Molluscan shellfish
(clam, oysters, abalone, etc.) can be allergenic, but reactions to these
shellfish are less common.
Symptoms of allergic reactions to foods
The most common allergic skin reaction to a food is hives. Hives are
red, very itchy, swollen areas of the skin that may arise suddenly and leave
quickly. They often appear in clusters, with new clusters appearing as other
areas clear. Hives may occur alone or with other symptoms.
Atopic dermatitis, or eczema, a
skin condition characterized by itchy, scaly, red skin, can be triggered by
food allergy. This reaction is often chronic, occurring in individuals with
personal or family histories of allergies or asthma. Asthma symptoms such as
coughing, wheezing, or difficulty breathing due to narrowed airways may be
triggered by food allergy, especially in infants and children.
Gastrointestinal symptoms of food
allergy include vomiting, diarrhea and abdominal cramping, and sometimes a
red rash around the mouth, itching and swelling of the mouth and throat,
nausea, abdominal pain, swelling of the stomach and gas.
In infants, non-allergic, temporary reactions
to certain foods, especially fruits, are common. For example, a rash around
the mouth, due to natural acids in foods like tomatoes and oranges, or
diarrhea due to excess sugar in fruit juice or other beverages, occur with
some frequency. However, other reactions are allergic and may be caused by
traces of the offending food when eaten again. As they grow older, some
children may tolerate foods that previously caused allergic reactions with
the exception of peanuts and tree nut allergy.
Only 21% of patients with peanut allergy will
outgrow it. Periodic food allergy check-ups with appropriate food challenges
should be carried out under the supervision of an allergist/immunologist.
Severe allergic reactions
In severe cases, consuming a food to which one is allergic can cause a
life-threatening reaction called anaphylaxis - a systemic allergic
reaction that can be severe and sometimes fatal. The first signs of
anaphylaxis may be a feeling of warmth, flushing, tingling in the mouth or a
red, itchy rash. Other symptoms may include feelings of light-headedness,
shortness of breath, severe sneezing, anxiety, stomach or uterine cramps,
and/or vomiting and diarrhea. In severe cases, patients may experience a
drop in blood pressure that results in a loss of consciousness and shock.
Without immediate treatment, anaphylaxis may cause death.
Symptoms of anaphylaxis are reversed by
treatment with injectable epinephrine, antihistamines, and other emergency
measures. It is essential that anyone with symptoms suggesting possible
anaphylaxis get emergency treatment immediately.
Food intolerance and additive reactions
Food intolerance reactions are usually caused by factors in the diet other
than the proteins that make up food allergens. As mentioned, one of the most
common is lactose intolerance. Other food intolerance reactions may be
triggered by drug-like chemicals in some foods. Symptoms can include
nervousness after consuming caffeine in coffee or soft drinks, headaches
triggered by chemicals in cheese and chocolate, or various adverse reactions
to chemicals and preservatives added to food, called food additives. These
additives may cause adverse reactions in sensitive people. The most common
food additives that may cause reactions include benzoates, BHA and BHT, FD&C
dyes Yellow No. 5 and Red No. 3, monosodium glutamate (MSG),
nitrates/nitrites, parabens and sulfites. However, true allergic reactions
to food additives are very rare.
If you suspect you are allergic to a food
additive, an allergist/immunologist should be consulted for testing. The
best way to handle food additive sensitivity is to know which foods contain
certain additives, and to avoid the additives that cause problems for you.
An allergist/immunologist is the best qualified professional to diagnose
food allergy. Diagnosis requires a carefully organized and detailed
assessment of the problem. First, the allergist/immunologist will take a
thorough medical history, followed by a physical examination. The allergist
will inquire about the frequency, seasonality, severity and nature of the
symptoms, and will ask about the amount of time that elapses between eating
a food and any reaction.
Allergy skin tests may be helpful to
determine which foods, if any, are triggering a patient's allergic symptoms.
In skin testing, a small amount of liquid extract made from the food is
placed on the back or arm. In a test called a prick test, a needle is then
passed through the liquid on the top layer of the skin.
If the patient develops a wheal - a raised
bump or small hive - within 20 minutes, this positive response indicates a
possible allergy. If the patient does not develop a wheal, the test is
negative. It is uncommon for someone with a negative skin test to have an
IgE-mediated food allergy. Skin tests are not helpful when sensitivity to
simple foods such as sugars or chemical food additives is suspected.
Your doctor may also use blood tests, called
RAST testing or CAP-RAST, to diagnose food allergies. In
certain cases, such as severe eczema all over the body, an allergy skin test
cannot be done. Your doctor may recommend a food RAST blood test to obtain
the same information that can be found with a skin test. For diagnosis of
milk, egg, peanut or fish allergy, the level of the CAP-RAST test may help
predict future food allergy reactions to these foods. False positive results
may occur with both food allergy skin testing and blood testing. Food
challenges, described below, are often required to confirm the diagnosis.
The allergist/immunologist may suggest that
the patient keep a food diary, which is a detailed record listing foods
eaten, date, time and any symptoms that occurred after eating the food. When
an allergy to a single food is suspected, the allergist may recommend
eliminating the food for a time. If symptoms are relieved, the
allergist/immunologist may add the food to the diet once again to further
determine if it causes a reaction (however, this is never done when the
patient has a history of anaphylaxis).
If the diagnosis of food allergy remains in
doubt, the allergist/immunologist may recommend a "blinded" food and/or food
additive challenge test. These tests are conducted in the doctor's office,
or at times, in the hospital under close observation. Usually, the suspected
food or a neutral food, called a placebo, is fed to the patient in colorless
capsules, or in a non-allergenic slush or pudding. Neither the patient nor
the doctor knows whether the suspected food or the placebo is being eaten.
This is called a "double-blind" challenge. When properly performed, these
challenges are very reliable in establishing a concrete cause and effect
relationship between a food and an allergy symptom.
- Avoid the food. The best way to
treat food allergy is to avoid the specific foods that trigger the
- Ask about ingredients. To avoid
eating a "hidden" food allergen away from home, food-allergic individuals
must always inquire about ingredients when eating at restaurants or
- Read food labels. It is important
for food-allergic people to read food labels carefully and to become
familiar with technical or scientific names for foods. For example, milk
may not be listed as an ingredient on a label; rather, the label may list
casein (a milk protein), sodium caseinate or milk solids. Not every food
that contains wheat identifies it as such; sometimes wheat is listed as
gluten. Similarly, egg white is frequently listed as albumin. Government
agencies have been working toward improving food ingredient labeling so
food-allergic consumers can more easily determine which foods they may
need to avoid.
- Be prepared for emergencies.
Anaphylactic reactions caused by food allergies can be potentially
life-threatening. Those who have experienced an anaphylactic reaction to a
food must strictly avoid that food. They may need to carry and know how to
use injectable epinephrine and antihistamines to treat reactions due to
accidental ingestion. People who are commonly around the patient, such as
spouses, co-workers, school teachers or daycare workers, should also know
to use the injectable epinephrine. Those with food allergies should also
wear an identification bracelet that describes the allergy. If you have an
anaphylactic reaction after eating a food, it is essential that you have
someone take you to the emergency room, even if symptoms subside. For
proper diagnosis and treatment, make sure to get follow-up care from an
If you have food allergies, you may also
contact the Food Allergy and Anaphylaxis Network (FAAN) for support: (800)
929-4040 or www.foodallergy.org.
Your allergist/immunologist can provide
you with more information on adverse reactions to foods and food additives.
Tips to Remember are created by the
Public Education Committee of the American Academy of Allergy, Asthma and
Immunology. This brochure was updated in 2003.
The content of this brochure is for
informational purposes only. It is not intended to replace evaluation by a
physician. If you have questions or medical concerns, please contact your
American Academy of Allergy,
Asthma and Immunology
555 East Wells Street
Milwaukee, WI 53202-3823
Physician Referral and
AAAAI Web site