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HOW DO ANTIHISTAMINES WORK?
is a chemical that causes many of the symptoms of allergic
rhinitis: a runny nose, sneezing, itchiness of the nose, and a
blocked nose. Histamine is found naturally in the body, but the
amount of it increases during allergic reactions.
Antihistamines prevent histamine from causing
these symptoms. Antihistamines block receptors to which
histamine would normally attach to and initiate an allergic
As a result, sneezing, itchiness of the nose and eyes, and a
runny nose are reduced. Antihistamines are less good at clearing
a blocked nose. They also reduce itchiness of the eyes in people
There are two ways in which
corticosteroids can be taken:
Topical corticosteroids are applied directly to the nose
using pump sprays or dry powder
Systemic corticosteroids are given by mouth or by
Both topical and systemic corticosteroids
are effective at treating allergic rhinitis, but topical
corticosteroids are most commonly used because they are safer.
HOW DO DECONGESTANTS WORK?
A blocked nose is the result of increased blood
flow to the lining of the nose. This causes swelling and reduces
the space through which air can pass. A runny nose also reduces
air flow through the nose.
Decongestants cause blood vessels to become
narrow by mimicking a chemical found in the body
(norepinephrine) that naturally causes blood vessels to
The narrowing of blood vessels reduces the
volume of blood reaching the nose lining. This reduces any
swelling within the nose and provides a larger passage for air
to flow through.
Cromones are taken as nose or eye
solutions. They can be used to treat mild allergic rhinitis
symptoms. They work by blocking the release of inflammatory
substances that cause allergic rhinitis.
They are generally less effective than
topical steroids. They also need to be applied regularly.
However, cromones have virtually no side effects.
Cromones may be useful in people that
cannot use antihistamines. When taken before the start of the
pollen season, they may be helpful in reducing allergic symptoms
during the pollen season.