DIETS
Allergies
Allergies
An allergy is the body’s oversensitive immune
response to a substance that should normally be
harmless. Food allergies cause a variety of symptoms,
ranging from the uncomfortable to the life-threatening.
How allergies work
In people with food allergies, exposure to specific proteins in
particular kinds of food causes their body’s immune system to
react inappropriately. It triggers the release of chemicals into the
bloodstream that aggravate or inflame different parts of the body.
Food allergies may cause skin problems, such as itching and
eczema, and digestion issues including nausea and diarrhea.
Severe allergies may also cause asthmatic symptoms, or even
a systemic reaction—anaphylaxis—that can be fatal.
BACTERIA
Food allergies are on the rise in developed countries,
but scientists aren’t sure why. One popular idea, known
as the “hygiene hypothesis,” suggests that the fact our
children don’t encounter as many pathogens,
such as bacteria, as they used to has somehow
affected the natural development of their
immune systems. Another theory is that
modern lifestyles—including diet, antibiotics,
and hygiene—interfere with our gut flora.
We know these microbes moderate our
immune systems, so this interference
may affect how our immune cells are
primed, causing allergies.
ALLERGIES ON THE RISE
PEANUTS
FIRST EXPOSURE
Protein absorbed
The trigger food—in this case
peanuts—is ingested and the proteins in
it are broken down into amino acids, which
are absorbed through the gut. Exposure can
also be through skin contact or inhalation.
Mast cells
The antibodies bind to the surface of
white blood cells called mast cells, which
become sensitized. At this stage there are
no symptoms of an allergy, but the cells are
primed for a second exposure.
Antibodies produced
If allergic to peanuts, the body’s
immune cells produce antibodies that are
specific to the particular allergen. The
antibodies travel in the bloodstream.
1
3
2
Antibody released
by immune cell
Antibody bound
to mast cell
1–2 PERCENT OF ADULTS AND
8 PERCENT OF CHILDREN IN
THE UK HAVE A FOOD ALLERGY
N
O
S
Y
M
P
T
O
M
S
IMMUNE
CELL
MAST CELL
A
B
D
O
M
I
N
A
L
P
A
I
N
S
W
O
L
L
E
N
T
H
R
O
A
T
Amino acid
absorbed
into body
Protein in
peanut ingested
S
T
O
M
A
C
H
I
N
T
E
S
T
I
N
E
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DIETS
Allergies
207
How allergies are diagnosed
A combination of a detailed patient history
and either a skin prick test or blood test
for food-specific antibodies are used to
diagnose food allergies. Food exclusion,
and blind and placebo-controlled oral food
tests are also effective, but must be done
under careful supervision.
Treatment options
The main treatment for allergies is to avoid
the trigger food, but this isn’t always easy.
In severe cases, even tiny amounts of the
allergen can cause reactions. Medicines are
used to prevent and alleviate the symptoms
of allergic reactions. For mild allergies, such
as hayfever, antihistamines can help by
blocking receptors from binding
to histamine chemicals.
Chemicals such
as histamine
released
AUTOINJECTOR
SUBSEQUENT EXPOSURE
Proteins bind to antibodies
On subsequent exposure, mast cells
identify the protein allergen, which then
binds to the antibodies on the mast cells.
This activates a process called degranulation.
4
Protein bound
to antibody
PEANUTS
Emergency treatment
People with severe allergies may need
to carry with them two autoinjectors (a
spring-loaded syringe) of adrenaline for
emergency treatment. Adrenaline narrows
blood vessels, relieves blood pressure, and
reduces swelling.
Skin prick test
A medic pierces the patient’s skin with
tiny amounts of suspected allergens,
producing localized allergic responses
in the form of bumps and redness.
Mast cell releases chemicals
As the mast cell degranulates it
releases histamine and other chemicals
into the bloodstream. It is the effect of
these chemicals on the body that
produces different allergic symptoms.
5
Anaphylaxis
In severe cases,
known as anaphylaxis, the
whole body is affected over
a very short period, resulting
in a combination of extreme
symptoms that can include
throat swelling, severe
asthma, and a drop in
blood pressure. Emergency
treatment is necessary.
6
Chemicals
released over
entire body
Body-wide allergic
reaction
S
Y
M
P
T
O
M
S
O
C
C
U
R
SWOLLEN
LIPS
O
N
L
Y
I
N
E
X
T
R
E
M
E
C
A
S
E
S
A
B
D
O
M
I
N
A
L
P
A
I
N
S
W
O
L
L
E
N
T
H
R
O
A
T
MAST CELL
MAST
CELL
S
W
O
L
L
E
N
H
A
N
D
S
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DIETS
Allergies
207
How allergies are diagnosed
A combination of a detailed patient history
and either a skin prick test or blood test
for food-specific antibodies are used to
diagnose food allergies. Food exclusion,
and blind and placebo-controlled oral food
tests are also effective, but must be done
under careful supervision.
Treatment options
The main treatment for allergies is to avoid
the trigger food, but this isn’t always easy.
In severe cases, even tiny amounts of the
allergen can cause reactions. Medicines are
used to prevent and alleviate the symptoms
of allergic reactions. For mild allergies, such
as hayfever, antihistamines can help by
blocking receptors from binding
to histamine chemicals.
Chemicals such
as histamine
released
AUTOINJECTOR
SUBSEQUENT EXPOSURE
Proteins bind to antibodies
On subsequent exposure, mast cells
identify the protein allergen, which then
binds to the antibodies on the mast cells.
This activates a process called degranulation.
4
Protein bound
to antibody
PEANUTS
Emergency treatment
People with severe allergies may need
to carry with them two autoinjectors (a
spring-loaded syringe) of adrenaline for
emergency treatment. Adrenaline narrows
blood vessels, relieves blood pressure, and
reduces swelling.
Skin prick test
A medic pierces the patient’s skin with
tiny amounts of suspected allergens,
producing localized allergic responses
in the form of bumps and redness.
Mast cell releases chemicals
As the mast cell degranulates it
releases histamine and other chemicals
into the bloodstream. It is the effect of
these chemicals on the body that
produces different allergic symptoms.
5
Anaphylaxis
In severe cases,
known as anaphylaxis, the
whole body is affected over
a very short period, resulting
in a combination of extreme
symptoms that can include
throat swelling, severe
asthma, and a drop in
blood pressure. Emergency
treatment is necessary.
6
Chemicals
released over
entire body
Body-wide allergic
reaction
S
Y
M
P
T
O
M
S
O
C
C
U
R
SWOLLEN
LIPS
O
N
L
Y
I
N
E
X
T
R
E
M
E
C
A
S
E
S
A
B
D
O
M
I
N
A
L
P
A
I
N
S
W
O
L
L
E
N
T
H
R
O
A
T
MAST CELL
MAST
CELL
S
W
O
L
L
E
N
H
A
N
D
S
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