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what is Allergies and how much types

What IS Allergies?

Allergies are abnormal or hypersensitive responses by the body’s immune
system to substances that are usually harmless. When Latrell plays outside in the fall, he sneezes and his throat itches.
When Melinda pets her friend’s cat, her eyes start to water. When Annie
puts on her nickel-plated bracelet, her arm breaks out in hives. When
Mrs. Garcia feeds her baby formula* containing milk products, the baby
cries as if he has a stomachache. After Ben was stung by a bee, he suddenly
had trouble breathing.
These are all examples of Allergies reactions. For most people playing
outside, petting a cat, touching metal, or drinking milk cause no problems.
A bee sting hurts but is not life-threatening. However, for millions
of people with allergies, these substances and hundreds of others can cause
the immune system to leap into action. The result can be as mild as a
stuffy nose or as severe as death.
Common allergens A substance that triggers an allergic reaction by
some people’s immune systems is called an allergen.

Most Allergies fall into one of four main categories:

■ Substances that are inhaled from the air, such as pollen, dust, mold
spores, or pet dander*
■ Substances that come in contact with the skin, such as nickel in
costume jewelry, chemicals in cosmetics, or latex*
■ Foods, such as milk, eggs, wheat, shellfish, or peanuts or other nuts
■ Substances that are injected, such as penicillin or other medications
or the venom from an insect sting.
Allergic responses do not occur with the first exposure to an allergen.
The immune system must first become “sensitized” by at least one previous
exposure to the allergen or to a very similar substance. For example,
a person who is allergic to one type of penicillin will probably have an
allergic reaction to other types of penicillin.

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The Immune System
The human body’s immune system consists of specialized cells and organs
that are finely tuned to fight off disease-causing microorganisms*, abnormal
cells such as cancer cells, and toxins and other harmful substances. Allergies
result from immune-system responses to otherwise harmless substances.
Because allergies involve the immune system, they are distinguished from
hypersensitivity* to a substance or intolerance* for a food.
The immune system recognizes and responds to foreign substances
called antigens*. Antigens can be molecules (usually proteins) on the surfaces
of viruses, bacteria, parasites, fungi, or abnormal cells. Toxins, drugs,
chemicals, and foreign particles can also be antigens.
Humoral immunity refers to large proteins called antibodies* or
immunoglobulins* (im-mune-o-GLOB-u-linz), which are produced by
immune-system cells called B-lymphocytes. The immune system can produce
millions of different antibodies that circulate in the blood and are
present in almost all bodily fluids. Allergies are caused by a specific type
of antibody called immunoglobulin E or IgE. One end of an IgE antibody
has two antigen-binding sites that recognize and bind to a specific
allergen like two puzzle pieces fitting together. The other ends of all IgE
antibodies are the same and bind to the surface of connective-tissue cells
called mast cells. People with allergies have much higher levels of IgE in
their bodies than people without allergies. They may only have IgE antibodies
that bind to one allergen such as ragweed pollen that causes hay fever. Or they may have many different types of IgE antibodies and are,
therefore, allergic to many different substances.
Cellular or cell-mediated immunity refers to the specialized cells of
the immune system that directly attack foreign substances. These include
cells that engulf and destroy the antigen, such as macrophages, and white
blood cells called T-lymphocytes, which have receptors for specific antigens
and also help B cells to produce immunoglobulins.
Immediate hypersensitivity The most common form of allergy is
immediate hypersensitivity or Type I. It depends on both humoral* and
cellular* immunities.
Upon first exposure to an allergen such as ragweed pollen, the immune
system of a susceptible person becomes sensitized, which means it goes
through the following actions:
■ The pollen molecules bind to receptors on the surfaces of specific
B-lymphocytes.
■ Macrophages engulf and break the pollen grain up into tiny pieces
that are displayed on the surfaces of the macrophages, a process
called “antigen presentation.”
■ Antigen presentation activates T-lymphocytes, which stimulate
B-lymphocytes to produce large amounts of IgE that specifically
bind to the pollen.
■ The IgE antibodies migrate through the body and bind to receptors
on mast cells and similar cells called basophils. There are a great
many mast cells in the nose, eyes, lungs, stomach, and intestines,
each with tens of thousands of IgE antibodies on their surfaces.
The next time the person inhales ragweed pollen, pollen molecules
attach to their specific IgE antibodies on mast cells and basophils, causing
the cells to explode and release histamines and other inflammatory substances.
These substances produce symptoms of an inflammatory allergic
reaction and recruit other types of inflammatory immune-system cells to
the site, increasing the allergic response.
Whereas an allergen-IgE reaction in the respiratory system may cause
hay fever, in the skin it may cause a rash or hives. Food and some drug
allergies cause reactions in the digestive tract. These allergic reactions happen
within a few minutes after exposure to the allergen.
Delayed hypersensitivity Delayed hypersensitivity occurs with
some skin allergies. Delayed hypersensitivity does not involve humoral
immunity or antibodies. Rather T-lymphocytes that have been previously
sensitized by exposure to the allergen upon subsequent exposure
release chemicals called lymphokines. Lymphokines call up macrophages
to engulf and digest the allergen and any cells containing
traces of it. They also cause swelling, redness, tenderness, and rashes.
These symptoms may take up to 72 hours to appear after exposure to
the allergen.

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Hello, My Name Is Shahbaz Shahid From Pakistan. I'm a specialist in Internal medicine or general medicine (in Commonwealth nations) is the medical specialty dealing with the prevention, diagnosis, and treatment of adult diseases.if any question so please feel free contact us.

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