More than 50 million Americans suffer
from allergic diseases. One of the most common forms of allergies is an allergic reaction to something in the
air. Health experts estimate that 35 million Americans suffer from upper respiratory tract symptoms that are
allergic reactions to airborne allergens (substances that can cause an allergic reaction).
Allergies are the immune system's specific reaction to a normally
harmless substance such as pollens, certain foods, or medicines. There are two main types, seasonal and perennial.
The seasonal variety occurs at specific times of the year, while the perennial variety can happen year-round. In
many cases, successful treatment involves medication, reducing contact with specific allergens, or
Definition of an
Allergies occur when the body's immune
system reacts to a normally harmless substance -- one that does not bother most people. People who have
allergies are often sensitive to more than one substance. Examples of allergens that cause allergic reactions
House dust mites
Understanding the Immune
Normally, the immune system functions
as the body's defense against invading germs such as bacteria and viruses. In most allergic reactions, however,
the immune system is responding to a false alarm. When a person with allergies first comes into contact with an
allergen, the immune system treats the allergen as an invader and gets ready to attack.
The immune system does this by
generating large amounts of an antibody called immunoglobulin E, or IgE. Each IgE antibody is specific for one
particular substance. In the case of pollen allergies, each antibody is specific for one type of pollen. For
example, the immune system may produce one type of antibody to react against oak pollen and another against
The IgE molecules are special because
they are the only type of antibody that attaches tightly to the body's mast cells (a certain type of tissue
cell) and to basophils (a type of blood cell). The next time the allergen encounters its specific IgE, it
attaches to the antibody like a key fitting into a lock.
This action signals the cell connected to the IgE to release (and in some cases, to produce) powerful chemicals
that cause inflammation. Histamine is one of these chemicals. These chemicals act on tissues in various parts of
the body, such as the respiratory system, and cause allergy symptoms.
Research scientists do not know for
sure why one person develops allergies and another does not. It is believed that allergies originated millions
of years ago as a way for the human body to rid itself of parasites and invading worms. Scientists also believe
that some people inherit a tendency to be allergic from one or both parents. Children, for example, are more
likely to develop allergies if one or both parents have allergies. However, it is unlikely to inherit a tendency
to be allergic to any specific allergen.
Being exposed to allergens at times
when the body's defenses are lowered or weakened -- such as after a viral infection or during pregnancy -- also
seems to contribute to developing allergies.
Allergies can either be seasonal or
perennial. Seasonal allergies occur at specific times of the year, while perennial allergies can occur
throughout the year.
Of these two types of allergies,
perennial allergies tend to be more difficult to treat.
The allergens that most commonly cause
seasonal allergies are:
Fungi and molds
The allergens that most commonly cause
perennial allergies are:
Fungi or molds.
What Are the
The symptoms of allergies are familiar
to many. The most common airborne allergy symptoms include:
Sneezing, often with a runny or clogged nose
Coughing and postnasal drip
Itching eyes, nose, and throat
Conjunctivitis (inflammation of the membrane that covers the
"Allergic shiners" (dark circles under the eyes caused by increased blood
near the sinuses)
"Allergic salute" (in a child, persistent upward rubbing of the nose that
a crease mark on the nose).
Allergies Versus Chemical
Some people have allergy-like reactions
to the chemicals found in a wide variety of synthetic and natural substances. These substances can include
Although a person's symptoms may
resemble those of allergies, sensitivity to chemicals does not represent a true allergic reaction involving IgE
and the release of histamine or other chemicals.
Rather than a reaction to an allergen, the person is experiencing a reaction to a chemical irritant.
People with allergies may have a greater sensitivity to chemicals than those without allergies.