Causes, incidence, and risk factors
In a person with allergies, the first exposure to the allergen triggers the immune system to recognize the substance. Any exposure after that will usually result in symptoms.
When an allergen enters the body of a person with a sensitized immune system, histamine and other chemicals are released by certain cells. This causes itching, swelling, mucus production, muscle spasms, hives, rashes, and other symptoms.
Symptoms vary in severity from person to person. Most people have symptoms that cause discomfort without being life-threatening. A few people have life-threatening reactions (called anaphylaxis).
The part of the body contacted by the allergen will, in part, affect the symptoms. For example, allergens that are inhaled often cause nasal congestion, itchy nose and throat, mucus production, cough, or wheezing. A food allergen can cause nausea, vomiting, abdominal pain, cramping, diarrhea, or a severe, life-threatening reaction. Allergies to plants often cause skin rash. Drug allergies usually involve the whole body.
Some disorders may be associated with allergies. These include eczema and asthma, among others.
Common allergens include those that contact the skin, breathing passages, or the surface of the eye (such as pollen; see also allergy to mold, dander, dust). Food allergies and drug allergies are common. Allergic reactions can be caused by insect bites, jewelry, cosmetics, and almost any substance that contacts the body.
Some people have allergic-type reactions to hot or cold temperatures, sunlight, or other physical stimuli. In some persons, friction (rubbing or vigorously stroking the skin) will cause symptoms. (See also atopic dermatitis and contact dermatitis.)
Allergies are relatively common. Both hereditary and environmental factors have been found to play a role.
Signs and tests
Allergy testing may be required to determine if your symptoms are an actual allergy or caused by other problems. For example, eating contaminated food (food poisoning) may cause symptoms that resemble food allergies. Some medications (such as aspirin, ampicillin, and others) can produce non-allergic reactions, including rashes, that resemble drug allergies but are not true allergies.
Tests that may reveal the specific allergens include:
Of course, the best "treatment" is to avoid what causes your allergies in the first place. It may be impossible to completely avoid everything you are allergic to, but you can often take steps to reduce your exposure. This is especially important for food and drug allergies.
Medications that can be used to treat allergies include the following:
The most appropriate medication depends on the type and severity of symptoms. Specific illnesses that are caused by allergies (such as asthma, hay fever, and eczema) may require other treatments.
Allergy shots (immunotherapy) are occasionally recommended if the allergen cannot be avoided and symptoms are hard to control. Regular injections of the allergen are given, with each dose slightly larger than the previous dose. Allergy shots keep your body from over-reacting to the allergen. They do not work for everybody and require frequent doctor's visits.
Severe reactions (anaphylaxis) require epinephrine, which can be life saving when administered soon after exposure by patients themselves.
Some children may outgrow an allergy as the immune system becomes less sensitive to the allergen. This is particularly true of food allergies. However, as a general rule, once substances have provoked allergic reactions, they continue to affect the person.
Allergy shots may cause uncomfortable side effects (such as hives and rash) and may have dangerous outcomes (such as anaphylaxis). Allergy shots are most effective in allergens that cause hay fever symptoms and individuals with severe insect sting allergies, but not food allergies. While it may require years of treatment, it is effective in about two-thirds of cases.
Call for an appointment with your health care provider if severe symptoms of allergy occur, if previously successful treatment has become ineffective, or if symptoms appear severe or do not respond to treatment.
If there is a family history of eczema and allergies it is wise to discuss the implications for infant feeding with your child's doctor. The timing of introduction of solid foods in general, as well as of several specific foods, can help prevent some allergies.
There is also evidence that infants exposed to certain airborne allergens (such as dust mites and cat dander) may be less likely to develop related allergies. This is called the "hygiene hypothesis" and sprang from observations that infants on farms tend to have fewer allergies than those who grow up in environments that are more sterile.
Once allergies have developed, treating the allergies and carefully avoiding those things that cause reactions can prevent allergies in the future.
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