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Food Allergy (the immediate kind)
True
food allergy (the immediate kind) causes a
limited range of symptoms. Diagnosis is based on
the history of what happened when the food was eaten, supported by evidence from skin tests
and blood tests. The blood test looks for the
presence of a specific antibody (an immunoglobulin E or IgE antibody) to the food being tested.
Reactions may be almost
instantaneous, particularly where symptoms in the lips, tongue, mouth or throat are involved.
Anaphylaxis is the name given to a generalised allergic response that may include an
all-over rash, collapse, severe wheezing and sometimes throat or tongue swelling. It is the
most serious form of immediate food allergy; a few deaths occur each year from this cause.185
Sufferers of all but the mildest variety are advised to carry an adrenaline injection
for self administration should the need arise.
Conditions that may mimic food allergy
More
confusingly, reactions indistinguishable from true food allergy can sometimes occur when
histamine is released directly from foods causing a 'histamine rush'. Scombroid
food poisoning, a kind of false food allergy, is due to the early spoilage by bacteria
(putrefaction) of certain foods, most often fish belonging to the
genus scombroidae (e.g. tuna, mackerel). The
action of the bacteria can cause the release of sufficiently high levels of histamine to induce symptoms in whoever eats the food.
Although individuals vary in their level of sensitivity to histamine, provided the dose is
sufficiently high, all those who eat the food will be affected. Diagnosis of this condition is
mainly by suspicion, although this becomes heightened when skin prick test or blood test
results fail to confirm that a true food allergy to the suspect food is present.
False food allergy
A
number of other foods may cause minor 'food allergy' symptoms, even though skin prick or RAST
blood test to that food may not show evidence of a true allergy. Such foods may contain
histamine or other biologically active 'amine' compounds such as tyramine. Food additive
intolerance may also sometimes occur, and this may act by releasing amine compounds from
foods.
Another
range of chemical compounds in foods known as 'salicylates' are related to aspirin.
Avoidance of foods containing these compounds occasionally helps patients suffering from
chronic allergic conditions such as rhinitis, nasal polyps or urticaria, especially when
sensitivity aspirin as a drug is already evident. Avoidance of salicylate-containing
foods together with avoidance of food additives is also thought to be helpful in childhood
hyperactivity (ADHD - attention deficit, hyperactivity disorder).11
Recommended reading:
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Allergy Clinic
