Allergies

Definition

An allergy or allergic reaction is the body

foreign substance that enters or comes into contact with the body. Normally,

the body

In an allergy, the body overreacts to the allergen, which may be something

rather harmless. Allergic reactions may be caused by the production

of an antibody called immunoglobulin E (IgE).

’s response to an allergen, a’s immune system produces antibodies to fight disease.

Description

The experience of an allergy depends on the body system or tissues that

are affected, the severity of the reaction, and whether the substance that

triggers the allergy can be eliminated from the patient

situation. Some allergies affect only a small part of

the body, like a skin rash on the wrist caused by

touching certain metals in inexpensive costume

jewelry. Other allergies may affect several major

body systems, as in the severe reactions that some

people have to bee stings or certain medications.

These reactions are especially related to IgE antibodies.

Some allergies are caused by substances

that can be avoided, such as certain foods, while

others may be triggered by exposure to plant or

tree pollens that are hard to avoid when the plants

are in season.

In general, when a person who has allergies

comes into contact with an allergen, the person

immune system produces IgE antibodies that

are specific to that allergen. The IgE antibodies

trigger the release of a chemical called histamine.

The histamine, in turn, causes the tissue

swelling, difficult breathing, skin rash, watery eyes,

runny nose, and other symptoms of an allergy.

The release of the histamine often attracts

other cells from the immune system to the

affected part of the body, increasing the inflammation,

tissue swelling, and production of large amounts of mucus

’s—

otherwise making the patient

Researchers do not yet fully understand why some substances produce

allergies in susceptible people and others do not, nor why some

people do get allergies and others do not.

The most common types of allergies among people in North

America are:

’s symptoms worse.

•

Hay fever.

•

eyelid).

Allergic conjunctivitis (inflammation of the tissue that lines the

•

Asthma.

•

a hypersensitivity reaction that affects a part of the body that is not

in direct contact with the allergen. Hay fever and asthma are also

considered atopic allergies.

•

Hives.

•

foods, and certain medications. This

type of severe allergic reaction is called anaphylaxis.

Severe reactions to insect stings, certain

•

are caused by just eight foods: eggs, fish,

milk, peanuts, shellfish, soy, tree nuts (walnuts,

hazelnuts, almonds, etc.), and wheat.

Food allergies. Most cases of food allergies

•

contact dermatitis is an inflammation of

the skin caused by direct contact with an

allergen or irritating substance, such as

poison ivy, certain dyes, or certain metals,

especially nickel.

Contact dermatitis. In contrast to eczema,

Demographics

Allergies are very common health problems in

all age groups in the general population. About

50 million people in the United States suffer

from some type of allergy, many of them from

more than one. For example, about 20 percent

of people who get hay fever eventually develop

asthma, and some develop eczema as well.

Some statistics for specific allergies are as follows:

•

Hay fever: 20 percent of the population in developed countries.

•

Asthma: 20 million people in the United States.

•

developed countries.

Anaphylaxis: Affects between 1 and 3 percent of the population in

•

Eczema: about 15 million people in the United States.

•

Hives: 20 percent of the population in developed countries.

•

There are two major types of risk factors for allergies: genetics and

the environment. Allergies run in families, with allergic parents likely to

have allergic children. Children are not necessarily allergic to the same

substances as their parents. For example, the parent could be allergic to

ragweed pollen while the child is allergic to peanuts. In general, allergies

are more severe in children than adults. Several studies have shown that IgE

levels are highest in young children and fall rapidly in people between the

ages of ten and thirty years. Among children, boys are almost twice as likely

as girls to develop allergies, but the sex difference disappears among adults.

Environmental factors are thought to explain why the rate of allergic

diseases has increased around the world since the 1980s. These factors

include dietary changes, a rise in air pollution, an increase in the levels

of other allergens in the environment, and the fact that children are

exposed to fewer infectious diseases than they were in the past. Some

doctors think that exposure to and recovery from these diseases made

children less susceptible to allergies.

Causes and Symptoms

An allergic reaction is caused by the individual person

to an allergen.

The symptoms of allergies may appear in one or more body systems:

’s immune response

•

blisters.

Skin: Redness, itching, bumps or wheals, crusting, weeping patches,

•

stuffy or runny nose.

Respiratory tract:Wheezing, sneezing, coughing, difficulty breathing,

•

Digestive tract: Nausea, vomiting, diarrhea, stomach cramps.

•

Eyes: Itching, watering, bloodshot or puffy appearance.

•

Other: Headache, dizziness, ringing in the ears.

Diagnosis

In some cases the allergen is easy to identify because the person has a pattern

of symptoms that appears after exposure to the food, substance, or

other trigger. In other cases the person may have to consult a specialist to

identify the allergens that are causing the symptoms. The usual method

of testing involves either a skin test, in which a small quantity of a possible

allergen is injected under the skin, or a blood test known as the radioallergosorbent

test (RAST). The RAST test is usually done in place of the skin

test when the patient has had severe reactions to the allergen.

Treatment

Anaphylaxis is a medical emergency that requires immediate treatment by

a medical professional or emergency rescue team.

There is no cure for allergies. However, most can usually be treated

with antihistamines and other medications that the doctor may recommend,

depending on which part of the body is affected. The most important

step in treatment, however, is avoiding the allergen if at all possible.

Minimizing exposure to the allergen may involve installing air filters in

the home, eliminating certain foods from the diet, cleaning the house frequently,

moving to a part of the country with fewer pollen-producing

plants, or other measures that the doctor may recommend.

Another approach to treating hay fever, asthma, allergic conjunctivitis,

and some other allergies is desensitization, which is also called immunotherapy.

In desensitization, patients are given a series of injections of

their specific allergen under the skin, with the concentration of allergen

in the shots being gradually increased. It takes an average of eight to twelve

months for the patient to see results, however, and the injections must be

taken for at least three years and sometimes closer to five years.

Although several alternative therapies

traditional Chinese medicine, and naturopathy

for allergies, a long-term study conducted by the Mayo Clinic in

2006 concluded that none of these was effective.

—including herbal medicine,—have been tried as treatments

Prognosis

Most allergies are not life-threatening, the exceptions being anaphylaxis

and asthma. About 5,500 people die each year in the United States from

asthma and another 500 from anaphylaxis. In general, allergies tend to

become less severe as people grow older. The major exception is food

allergies (especially to peanuts), which can last a lifetime.

Prevention

There is no way to prevent people from developing allergies because the

genetic factors that are involved in allergic reactions have not been fully

understood. Desensitization therapy and avoidance of specific allergens

are the only effective methods of prevention at present.

The Future

Public health experts expect allergies of all types to become more

common in the developed countries in the future as a result of lifestyle

changes and a larger proportion of the world

cities. As of 2008, some researchers were working on a vaccine that would

target the IgE antibody itself. The vaccine is expected to be more effective

than current desensitization therapy in preventing allergies.

SEE ALSO

Hay fever; HivesAnaphylaxis; Asthma; Conjunctivitis; Dermatitis; Eczema;’s population living in largeFood allergies: about 8 percent of school-age children.Eczema. Eczema is sometimes called atopic dermatitis because it is’s diet or living

Allergies