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HOW ALLERGIC REACTIONS WORK
An allergic reaction involves two features of the human immune response.
One is the production of immunoglobulin E (IgE), a type of protein called
an antibody that circulates through the blood. The other is the mast
cell, a specific cell that occurs in all body tissues but is especially
common in areas of the body that are typical sites of allergic reactions,
including the nose and throat, lungs, skin, and gastrointestinal tract.
Food allergies are usually inherited - if allergies of any kind are
common in a family, then developing food allergies will be more likely,
especially if both parents have allergies of some kind.
Before an allergic reaction can occur, the person has to be exposed
to the foods s/he is allergic to. As this food is digested, it triggers
the allergic response, generating these antibodies in large amounts
which then attach to these mast cells. The next time the person eats
that food, it interacts with those antibodies and triggers the mast
cells to release chemicals such as histamine. The location of the body
these cells are in will determine the location of the allergic response.
For example, if these cells are in the intestines, the person may have
abdominal pain or diarrhea. The chemicals released by mast cells in
the skin can cause hives.
The digestion process affects the timing and the location of a reaction.
The initial reaction may be a tingling or itching sensation as they
start to eat the food, then reactions may occur in the stomach and abdominal
region, and as the allergens travel through the bloodstream, possibly
a drop in blood pressure, hives or eczema may occur as well, or even
trigger an asthma attack when the allergens reach the lungs. All or
part of these types of reactions can occur between near-instantaneous
to an hour or so after ingesting the offending food.
COMMON ALLERGENS
Although an individual could be allergic to any food, such as fruits,
vegetables, and meats, they are not as common as the following eight
foods which account for 90% of all food-allergic reactions: Milk, Egg,
Peanuts (one of the chief foods that cause severe anaphylaxis), Tree
nut (walnut, cashew, etc.), Fish, Shellfish (shrimp, crayfish, lobster,
crab and so on), Soy and Wheat (gluten).
Other allergens include medications, insect stings (such as bees),
and latex (particularly common among healthcare workers.)
Food allergies vary in severity, from life threatening to just a nuisance
rash. Reactions are sometimes dose-dependent: trace or small amounts
may be fine, but larger amounts may trigger a reaction, however severe.
If you are allergic to one specific food in a food family other foods
in the same food family (i.e., dairy products) may cause a similar reaction,
even if you're not already aware of it. The foods that adults or children
react to are usually those foods they eat more often. In Japan, for
example, rice allergy is more frequent. In Scandinavia, codfish allergy
is more common.
CROSS REACTIVITY
If someone has a life-threatening reaction to a certain food, doctors
will usually advise them to avoid similar foods. For example, a history
of allergy to shrimp will usually indicate cross-reactivity to other
shellfish such as lobster or crab as well.
During pollen seasons, people allergic to particular pollens or ragweed
may find they have a reaction when eating melons or fruits. This is
likely due to pollen dust resting on the skin of the fruit, or when
the fruit is sliced (such as cantaloupe), some of the pollen dust then
gets dragged into the rest of the fruit on the surface of the knife.
ANAPHYLAXIS
A sudden, severe, potentially fatal, systemic allergic reaction that
can involve various areas of the body (such as the skin, respiratory
tract, gastrointestinal tract, and cardiovascular system). Symptoms
occur within minutes to two hours after contact with the allergy-causing
substance, but in rare instances may occur up to four hours later. Anaphylactic
reactions can be mild to life-threatening.
Common causes of anaphylaxis include: Food (such as peanuts), medications,
insect stings (bee stings being a common severe allergen), and latex
(particularly common among healthcare workers). Anyone with a history
of anaphylactic reactions is at risk for another severe reaction.
DIFFERENTIAL DIAGNOSIS
While "allergy" and "intolerance" are often used
interchangeably, they are really two different things. A food intolerance
is an adverse food-induced reaction that does NOT involve the immune
system - lactose intolerance is one example, or MSG sensitivity, or
reactions to things like Nutrasweet. When a lactose intolerant person
eats or drinks something that is milk based, symptoms such as gas, bloating,
or abdominal pain may occur because the person's body lacks an enzyme
that is needed to digest milk products. This usually does not always
have the potential to be fatal, merely inconvenient, painful or embarrassing.
Food poisoning:
Sometimes food poisoning symptoms will mimic the symptoms of a food
allergy.
Adverse Reactions:
Another intolerance example is an adverse reaction to certain components
that are included in food to enhance taste, color, or preserve it.
Such substances can include artificial colors and flavors (One reaction
to artificial colors/flavors in foods, particularly in children, is
"hyperactivity" or attention deficit disorder. It's not,
however, the only ADD cause.) MSG and sulfites are other items that
can generate an intolerant reaction.
Gluten sensitivity, or Celiac Syndrome, is another common adverse reaction
- this is cause by an abnormal immune response to gluten, which is a
component in wheat and other grains. Because gluten and gluten byproducts
make their way into a LOT of foods, someone with this problem has to
spend a lot of time reading labels to be sure there's not wheat or gluten
products.
DISCOVERING FOOD ALLERGENS
The first step is to find out what you're allergic to. Keep a food
diary for at least 1-2 weeks. Log any and all negative reactions you
get, regardless of when they happen. Log any and all foods you eat,
drink or snack on, even if it's just "a nibble of so-and-so's sandwich".
Log anything you eat or drink in-between meals as well. Log all medication
you may be taking (sometimes a medication taken on an empty stomach
will give you abdominal pains, but be OK once you've had food) and when
you take it. This information can tell you (or your doctor) what you
may be allergic to.
Questions to keep in mind when keeping a food diary (and your doctor
will most likely ask similar questions, if not more) are:
What was the timing of the reaction? Did the reaction come on quickly,
usually within an hour after eating the food?
Is the reaction always associated with a certain food?
Did anyone else get sick? For example, if the person has eaten contaminated
fish, everyone who ate the fish should be sick. In an allergic reaction,
however, only the person actually allergic to the fish becomes ill.
How much did the patient eat before experiencing a reaction? The
severity of the patient’s reaction is sometimes related to the
amount of food the patient ate.
How was the food prepared? Some people will have a violent allergic
reaction only to raw or undercooked fish. Complete cooking of the
fish destroys those allergens in the fish to which they react. If
the fish is cooked thoroughly, they can eat it with no allergic reaction.
Were other foods ingested at the same time of the allergic reaction?
Some foods may delay digestion and thus delay the onset of the allergic
reaction.
The next step is a true elimination diet. Pick a food or food group
(i.e., milk or dairy products) and eliminate it for two weeks to a month.
Observe your reactions, whether they change or stay the same. After
this period of time, put that food/food group back in your diet and
eliminate another food/food group (i.e., shellfish) for another two
weeks to a month. Again, observe your reactions, whether they change
or stay the same. Repeat this until you've worked through all the foods
you usually eat, or you find out what causes a reaction, whichever comes
first.
Once you've gone through the elimination diet, you should know what
foods you're allergic to, or if you're allergic to any foods. (Sometimes
what can seem like a food allergy can be a case of food poisoning due
to bad food preparation/storage in a restaurant.)
TREATING FOOD ALLERGIES
Food allergies are easily (if annoyingly) treated by dietary avoidance
- once the food allergens are identified, the food must be removed from
the person's diet. This requires reading of lengthy ingredient lists
for each item they are considering eating. Foods such as peanuts, eggs
and milk often show up in foods that would not normally be associated
with them, or there are trace amounts stemming from "shared equipment"
(the equipment is used for multiple types of food) used in the preparing
factory.
I will admit it IS a pain in the ass to read every single label to
find the allergens you react to - however, the end result of a more
comfortable life IS worth the trouble.
People that are highly allergic to an item (such as peanuts) cannot
tolerate even the smallest amounts without having a reaction. People
who's allergies are mild to moderate can tolerate small amounts with
little to no discomfort.
~SphynxCatVP, Sept 2004
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