Food allergies are set off by the protein complexes in certain things.
Note that is specifically for allergies rather than for any of the
range of sensitivities that sometimes are termed allergies. What the
individual becomes allergic to depends on several factors:
1. Is the individual genetically prone to allergies? Some are. Such
individuals may be allergic to multiple things, not just one thing
or one category.
2. Is the individual among those in the increased rate of allergic
individuals? There are multiple possible reasons for this that have
been studied or are under study. One that has some decent support
from studies is that the world today may simply be too clean for some
individuals, but since the increases in cleanliness are attached to
hugely improved lifespans and decreased rates of illness it is a "six
of one and a half dozen of the other" situation till more is known.
The basic hypothesis is that the immune systems of some, when not used
in the ways for which they exist, may be more prone to malfunction.
3. Is the item one to which the individual was exposed many times?
Allergies are more likely to happen with foods that are often eaten
which is why in northern Asia wheat is the more common grain allergy
but in southern Asia rice is. It is also why people who are prone to
multiple food allergies tend to lose the ability to have a number of
their favorite foods. This is also probably why chicken is such a
common ferret allergen since it is in so many ferret foods. This is
very, very, very important to remember. It is the key factor that
people are most likely to forget about allergies.
4. Is the food item one that is more prone to causing allergic
reactions? Some are. Crustaceans like lobster, crab and shrimp are
in that category, for example.

Some allergies go away after the juvenile years; others remain. The
most likely ages to develop allergies are when the immune system is
strongest which is why the twenties plus or minus a few years are so
common in people for allergy starts.

What the individual has as an allergen depends on the individual. There
are those with allergies to things that are less commonly or even
rarely allergens. It just happens some times for various reasons.

To understand why commonly eaten foods are more likely to cause
allergies it is important to know how allergic reaction begin to
happen. Basically, during some exposure to the item the immune system
misidentifies a protein complex in the item as being from an invader.
Then the NEXT time there is an exposure the body reacts. That is why
the more exposures there are the more chance there is of reacting.
Again: More exposures to the protein complex = more chances to
misidentify that protein complex and become allergic. (Yes, some people
lose the ability to have their favorite foods and so can ferrets.)

BTW: with vaccinations it may also be that if there is already an
extremely good resistance (as shown in very unusually high titer
levels) then the chances of having an allergic reaction may be
increased. We personally, have gone to titers every year or two
(depending on age, vaccination history, and previous titer levels) and
to vaccinating if the titer levels are low but not otherwise. One of
ours always needed an annual vaccination because he could not keep his
titer levels up but two consistently had terribly high levels and might
have been at increased risk of reaction and just plain never needed
new CD vaccinations. Most of ours have been in the middle ground.

Okay, what is or is not a reaction and what types of reactions exist?
After something like a vaccination if the vaccine is working you expect
a day or so of the blahs because that means the immune system is
actually doing the right thing and identifying the protein complex
message carried in the vaccine as being an invader. That is also a
very, very important thing that many people forget so reread that and
expect the blahs if the vaccine is working right. After eating, though,
you don't normally expect to get sick. Some do and for a variety of
reasons. There are an assortment of reasons why some foods may not
be broken down well: gall bladder disease, genetic and or enzymatic
variations in the individuals, small intestinal damage which means that
some nutrients can not be taken up properly or other differences with
similar results, etc. Not all problems with foods are allergies; in
fact, in humans most problems with foods are not actual allergies.
This is the third thing that most people forget: most problems with
foods are NOT allergies.

When a severe food allergy happens here are the things that can occur:

With an anaphylactic reaction there is a rapid motion of fluid from
the blood stream and into tissues and the intestine. The sudden drop
in blood pressure can lead to dizziness or even loss of consciousness.
Flux, which can be bloody if the fluid transit is so fast that it
carries blood cells across the membranes into the intestines, can
happen. Mucus membranes swell. This can result in the respiratory tract
swelling so badly that the individual smothers. Sometimes other tissues
can swell like the tongue or the face. Low blood pressure can cause
problems with heart or brain function if bad enough. The key med for
an anaphylactic reaction is epinephrine but steroids or even Singulair
may be used to reduce inflammation in the lungs, steroids and
antihistamines can reduce the reaction and reduce inflammation in
general, IV fluids can bring up blood pressure, and oxygen can protect
the brain and more.

If a Stevens Johnson reaction happens then there may be itching, rash,
blisters, joint aches, or tissue necrosis. Stevens Johnson can cause
enough mucus membrane necrosis to be fatal and must be taken seriously.
Such a reaction needs longer term follow-up.

(It is possible to have tissue necrosis from mucus membrane blisters
with an anaphylactic reaction, too, BTW, and that needs to be assessed
as well to be sure what it happening. Some individuals blister so fast
and badly in their mouths with food allergens that they can spit out
the foods before worse happens but that is rare.)

Some with food allergies will have asthmatic reactions, which can be
severe ones, if those foods go airborne as when they are cooked or
are circulated in recycled air like in an airplane.

I feel like I am forgetting to include something. Oh, well...

Hypoallergenic foods and why they help many: Hypoallergenic foods do
not work for all critters with food allergies but do work for most
because they are processed in ways that break most of the protein
complexes down to the amino acids that create proteins. Usually, the
better solution is to feed a different type of food.

Some food allergies are to only specific foods, but some are the
general categories which are related or which have a protein complex
in common. So, while a number of ferrets with chicken allergy are only
allergic to chicken some will instead react to all poultry. (With
vaccines some individuals are allergic to specific vaccines but others
might be allergic to something in the liquid medium in which the
vaccine is delivered and those rare ones may be allergic to multiple
vaccines.)

Yes, some ferrets do become allergic to things other than commonly
eaten, high protein level chicken. The way that allergies happen
combined with the contents of most ferret foods, though, makes the
chicken a more likely cause. Certainly, some ferrets have other food
problems, especially those who have small intestinal damage as from ECE
in the past which may make things like grains more irritating which is
a completely different problem but a problem, nevertheless.

Sukie (not a vet) Ferrets make the world a game.

[addendum:]
>Food allergies are set off by the protein complexes in certain things.
>Note that is specifically for allergies rather than for any of the
>range of sensitivities...

I worded that badly. What here is specifically for allergies is the
POST, not what sets off the problems. My apologies for being unclear
on that score.

Sukie (not a vet)  Ferrets make the world a game.

Recommended ferret health links:
http://pets.groups.yahoo.com/group/ferrethealth/
http://ferrethealth.org/archive/
http://www.miamiferret.org/
http://www.ferrethealth.msu.edu/
http://www.ferretcongress.org/
http://www.trifl.org/index.shtml
http://homepage.mac.com/sukie/sukiesferretlinks.html
all ferret topics:
http://listserv.ferretmailinglist.org/archives/ferret-search.html

"All hail the procrastinators for they shall rule the world tomorrow."
(2010, Steve Crandall)

A nation is as free as the least within it.

[Posted in FML 7660]