WEBVTT

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In people with an allergy
the immune system over-reacts

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to a foreign substance
that is actually harmless.

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These substances
are referred to as allergens.

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Typical allergens include:

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• pollen

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• dust mite droppings

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• substances in the saliva or sweat
of pets and livestock

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(often referred to
as animal hair allergies)

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• insect stings

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• proteins in food
such as nuts, seafood or strawberries

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• medication

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• spores or mold fragments

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• and contact allergens
(e.g., metals or perfumes)

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Allergic reactions are most common

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• in the airways

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• on the skin

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• and mucous membranes.

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Symptoms occur mostly on parts of the body

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that have come into direct contact
with an allergen

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and very frequently occur
immediately after contact,

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but may also take hours or days to appear.

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Symptoms can be mild
but can also be very distressing

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and have an impact on daily life.

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They may be seasonal
(such as hay fever, for example)

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or occur all year round, such as
house dust mite and mold allergies.

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Typical symptoms of allergies include,

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depending
on the allergen and individual sensitivity:

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• rhinitis, coughing and sneezing,

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• respiratory problems,

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• streaming eyes,

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• itching,

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• skin rashes,

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• swelling in the mucous membranes,

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• and gastrointestinal problems.

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Allergies to

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• foods,

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• insect stings,

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• or certain active substances in medicines

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can cause an anaphylactic reaction:

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a sudden, severe immune response

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that in the worst case (anaphylactic shock)
can affect the entire body.

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This is an emergency situation
and can be life-threatening.

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In people who are susceptible to allergies

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the immune system reacts

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when it first comes into contact
with the allergen

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in the same way that it would react
to a pathogen or other invading organism.

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It creates antibodies to it.

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These antibodies detect the allergen

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if the body comes into
contact with it again.

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Mast cells, for example, release histamine,
a chemical that is part

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of the immune system’s normal defense
against pathogens

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but in this case is unnecessary
and may even be harmful.

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Histamine triggers
an inflammatory reaction,

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particularly swelling of tissue.

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And it is this that causes the symptoms
in many allergies.

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The precise reason for this overreaction
is still unclear,

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though predisposition

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and environmental factors are involved.

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Most allergies begin in childhood

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but may also develop later in life.

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There are also certain allergies
that disappear in adulthood.

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In short:

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In people with an allergy

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the immune system responds
to a harmless substance such as:

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• pollen,

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• dust mite excrement,

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• or food ingredients.

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This triggers
characteristic allergic reactions such as:

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• runny nose,

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• respiratory problems

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• or skin rashes.

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Factors affecting whether
and when people develop allergies

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are likely to be both genetic

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and environmental.

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Allergies mostly start early in life

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but can also occur later

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or even clear up later in some cases.