Allergy Symptoms, Causes, Treatment - What causes allergies? on MedicineNet

MedicineNet.com

About Us | Privacy Policy | Site Map
February 9, 2012

Allergy (cont.)

Medical Author:
Medical Editor:

What causes allergies?

To help answer this question, let's look at a common household example. A few months after the new cat arrives in the house, dad begins to have itchy eyes and episodes of sneezing. One of the three children develops coughing and wheezing, especially when the cat comes into her bedroom. The mom and the other two children experience no reaction whatsoever to the presence of the cat. How can we explain this?

The immune system is the body's organized defense mechanism against foreign invaders, particularly infections. Its job is to recognize and react to these foreign substances, which are called antigens. Antigens are substances that are capable of causing the production of antibodies. Antigens may or may not lead to an allergic reaction. Allergens are certain antigens that cause an allergic reaction and the production of IgE.

The aim of the immune system is to mobilize its forces at the site of invasion and destroy the enemy. One of the ways it does this is to create protective proteins called antibodies that are specifically targeted against particular foreign substances. These antibodies, or immunoglobulins (IgG, IgM, IgA, IgD), are protective and help destroy a foreign particle by attaching to its surface, thereby making it easier for other immune cells to destroy it. The allergic person however, develops a specific type of antibody called immunoglobulin E, or IgE, in response to certain normally harmless foreign substances, such as cat dander. To summarize, immunoglobulins are a group of protein molecules that act as antibodies. There are five different types; IgA, IgM, IgG, IgD, and IgE. IgE is the allergy antibody.

(In 1967, the husband and wife team of Kimishige and Teriko Ishizaka detected a previously unrecognized type of immunoglobulin in allergic people. They called it gamma E globulin or IgE.)

In the pet cat example, the dad and the youngest daughter developed IgE antibodies in large amounts that were targeted against the cat allergen, the cat dander. The dad and daughter are now sensitized or prone to develop allergic reactions on subsequent and repeated exposures to cat allergen. Typically, there is a period of "sensitization" ranging from months to years prior to an allergic reaction. Although it might occasionally appear that an allergic reaction has occurred on the first exposure to the allergen, there must have been a prior contact in order for the immune system to be poised to react in this way.

IgE is an antibody that all of us have in small amounts. Allergic persons, however, produce IgE in large quantities. Normally, this antibody is important in protecting us from parasites, but not from cat dander or other allergens. During the sensitization period, cat dander IgE is being overproduced and coats certain potentially explosive cells that contain chemicals. These cells are capable of causing an allergic reaction on subsequent exposures to the dander. This is because the reaction of the cat dander with the dander IgE irritates the cells and leads to the release of various chemicals, including histamine. These chemicals, in turn, cause inflammation and the typical allergic symptoms. This is how the immune system becomes exaggerated and primed to cause an allergic reaction when stimulated by an allergen.

On exposure to cat dander, the mom and the other two children produce other classes of antibodies, none of which cause allergic reactions. In these non-allergic members of the family, the dander particles are eliminated uneventfully by the immune system and the cat has no effect on them.

Figure 1

The Immune System
-

Foreign Substance

alt="-"
(cat dander, pollen, virus, bacteria)
*
*

Normal Immune Response

IgM, IgG, IgA, IgD and various immune cells respond to attack.

Exaggerated Immune Response

IgE is overproduced in response to cat dander, pollens, and other harmless allergens.

*

*

Foreign substance is eliminated.

Subsequent exposure results in an allergic reaction.

*

*

Non-Allergic Individual

Allergic Individual


Patient Discussions

Viewers share their comments

Allergy - Symptoms Question: What symptoms did you experience with your allergies?
Allergies - Describe Your Experience Question: Please describe your experience with allergies.

MedicineNet Doctors

Suggested Reading on Allergy by Our Doctors

  • Related Diseases & Conditions

    • Eczema
      • Eczema, also known as dermatitis, is a general term for many types of skin inflammation. The most common form of eczema is atopic dermatitis. The other forms of eczema include: contact eczema, seborrheic eczema, Nummular eczema, Neurodermatitis, stasis dermatitis, and dyshidrotic eczema. Symptoms, diagnosis, and treatment of eczema may vary from person to person and may depend on the type of eczema.
    • Pink Eye
      • Pink eye, also called conjunctivitis, is redness or irritation of the conjunctivae, the membranes on the inner part of the eyelids and the membranes covering the whites of the eyes. These membranes react to a wide range of bacteria, viruses, allergy-provoking agents, irritants, and toxic agents.
    • Sinus Infection
      • Sinus infection (sinusitis) signs and symptoms include headache, fever, and facial tenderness, pressure, or pain. Treatments of sinus infections are generally with antibiotics and at times, home remedies.
    • Chronic Rhinitis and Post-Nasal Drip
      • Allergic rhinitis symptoms include an itchy, runny nose, sneezing, itchy ears, eyes, and throat. Seasonal allergic rhinitis (also called hay fever) is usually caused by pollen in the air. Perennial allergic rhinitis is a type of chronic rhinitis and is a year–round problem, often caused by indoor allergens, such as dust, animal dander, and pollens that may exist at the time. Treatment of chronic rhinitis and post nasal drip are dependant upon the type of rhinitis condition.
    • Hives
      • Hives, also called urticaria, is a raised, itchy area of skin that is usually a sign of an allergic reaction. The allergy may be to food or medications, but usually the cause of the allergy (the allergen) is unknown.
    • Itching
      • Itching can be a common problem. Itches can be localized or generalized. There are many causes of itching to include: infection (jock itch, vaginal itch), disease (hyperthyroidism, liver or kidney), reactions to drugs, and skin infestations (pubic or body lice). Treatment for itching varies depending on the cause of the itch.
    • Atopic Dermatitis
      • Eczema is a general term for many types dermatitis (skin inflammation). Atopic dermatitis is the most common of the many types of eczema. Other types of eczema include: contact eczema, allergic contact eczema, seborrheic eczema, nummular eczema, stasis dermatitis, and. dyshidrotic eczema.
    • Food Allergy
      • The most common food allergies are to eggs, nuts, milk, peanuts, fish, shellfish, strawberries and tomatoes. Symptoms and signs include nausea, vomiting, diarrhea, abdominal pain, itching, hives, eczema, asthma, lightheadedness, and anaphylaxis. Allergy skin tests, RAST, and ELISA tests may be used to diagnose a food allergy. Though dietary avoidance may be sufficient treatment for mild allergies, the use of an Epipen may be necessary for severe food allergies.
    • Asthma
      • Asthma is a common disorder in which chronic inflammation of the bronchial tubes (bronchi) makes them swell, narrowing the airways. Signs and symptoms include shortness of breath, chest tightness, cough and wheezing.
    • Colic in Babies
      • Colic is crying or fussing that begins suddenly, lasting for a total of three hours a day and happening more than three days a week for about three weeks. Symptoms include the baby's face turning red, the belly is distended, the feet may be cold, the hands clenched, and the legs may alternate between being flexed or extended. Treatment may involve ruling out other causes of the fussing and the doctor prescribing anti-gas bubbly medicine.
    • Sinus Headache
      • Sinus headache is caused by a sinus infection or inflammation of the sinus cavities. The primary symptom of a sinus infection is pain and increasing pressure overlying the area and associated tenderness to the touch. Treatment of a sinus headache depends on the cause.
    • Eye Allergy
      • Eye allergy (or allergic eye disease) are typically associated with hay fever and atopic dermatitis. Medications and cosmetics may cause eye allergies. Allergic eye conditions include allergic conjunctivitis, conjunctivitis with atopic dermatitis, vernal keratoconjunctivitis, and giant papillary conjunctivitis. Dry eye, tear-duct obstruction, and conjunctivitis due to infection are frequently confused with eye allergies. Eye allergies may be treated with topical antihistamines, decongestants, topical mast-cell stabilizers, topical antiinflammatory drugs, systemic medications, and allergy shots.
    • Cold, Flu, Allergy Treatments
      • Before treating a cold, the flu, or allergies with over-the-counter (OTC) medications, it's important to know what's causing the symptoms, which symptoms one wishes to relieve, and the active ingredients in the OTC product. Taking products that only contain the medications needed for relieving your symptoms prevents ingestion of unnecessary medications and reduces the chances of side effects.
    • Anaphylaxis
      • Anaphylaxis is a serious allergic reaction that affects a number of different areas of the body at one time, and can be fatal. Causes of anaphylaxis can be food allergy, latex allergy, allergy to insect or but stings/bites, asthma, or other materials or conditions. Symptoms include flushing, itching, hives, anxiety, rapid or irregular pulse. Severe symptoms may be throat and tongue swelling, swallowing, and difficulty breathing. Some disorders appear similar to anaphylaxis such as fainting, panic attacks, blood clots in the lungs, heart attacks, and septic shock. If you think that you may be having an anaphylactic reaction, seek emergency care or call 911 immedately.
    • Mold
      • Mold exposure may cause symptoms in people who are sensitive to molds. Symptoms of mold allergy include sneezing, runny nose, wheezing, coughing, redness of the eyes, and rash. Prevent mold growth by keeping indoor humidity low, between 30%-50%, using bathroom fans when showering, repairing plumbing leaks quickly, and using an air conditioner during humid seasons.
    • Hoarseness
      • Hoarseness (abnormal deep, harsh, raspy voice) is caused by a variety of conditions in which the larynx (voice box and vocal chords) are irritated or injured. Examples of causes of hoarseness include: laryngitis, straining the vocal cords by yelling or screaming, infections, GERD, allergies, and more. Treatment of hoarseness depends on the cause.
    • Asthma in Children
      • Asthma, the main cause of chronic illness in children, has signs and symptoms in children that include frequent coughing spells, low energy while playing, complaints of chest "hurting," wheezing while breathing, shortness of breath, and feelings of tiredness. Treatment will involve a doctor creating an asthma action plan which will describe the use of asthma medications and when to seek emergency care for the child.
    • Blepharitis
      • Blepharitis is inflammation of the eyelids. Acne rosacea, Staphylococcal bacteria, allergies, sensitivities to makeup or contact lens solutions, head lice, or other conditions may cause blepharitis. Symptoms and signs include itchy eyelids, burning sensation in the eyes, crusting of the eyelids, light sensitivity, red, swollen eyelids, loss of eyelashes, and dandruff of the lashes and eyebrows. Proper eyelid hygiene and a regular cleaning routine controls blepharitis.
    • Poison Ivy
      • Poison ivy, oak, and sumac are plants that cause an itchy skin rash and skin inflamation when contacted directly. This poison can be treated with medications such as calamine lotion and cortisone drugs.
    • Hay Fever
      • Hay fever (allergic rhinitis) is an irritation of the nose caused by pollen and is associated with the following allergic symptoms: nasal congestion, runny nose, sneezing, eye and nose itching, and tearing eyes. Avoidance of known allergens is the recommended treatment, but if this is not possible, antihistamines, decongestants, and nasal sprays may help alleviate symptoms.
    • Breastfeeding and Formula Feeding
      • It's important to know whether you will breastfeed or bottle-feed your baby prior to delivery, as the breasts' ability to produce milk diminishes soon after childbirth without the stimulation of breastfeeding. Breast milk is easily digested by babies and contains infection-fighting antibodies and cholesterol, which promotes brain growth. Formula-fed babies actually need to eat somewhat less often since formula is less readily digested by the baby than human milk. This article explores the advantages and disadvantages of both forms of feeding.
    • Allergy Treatment Begins At Home
    • Nasal Allergy Medications
    • Bee and Wasp Sting
      • Bees, wasps, and fire ants are related insects that belong to the Hymenoptera order. There are thousands of species of wasps found throughout the world. Common wasps are yellow jackets and hornets. Types of bees include honey bees, the Africanized honey bee (killer bee), and the bumble bee. There are four types of reactions to a bee or wasp sting; 1) local reaction, 2) systemic allergic reaction, 3) toxic reaction, and 4) delayed reaction. Individuals who have a systemic or toxic reaction generally require immediate medical treatment to prevent anaphylactic reaction, and possibly death.
    • Latex Allergy
    • Adult-Onset Asthma
      • Adult-onset asthma is asthma that is diagnosed in people over 20 years of age. Symptoms include wheezing, coughing, shortness of breath and difficulty breathing. Treatment may involve anti-inflammatory medications or bronchodilators.
    • Bug Bites and Stings
      • Bug bites and stings have been known to transmit insect-borne illnesses such as West Nile virus, Rocky Mountain spotted fever, and Lyme disease. Though most reactions to insect bites and stings are mild, some reactions may be life-threatening. Preventing bug bites and stings with insect repellant, wearing the proper protective attire, and not wearing heavily scented perfumes when in grassy, wooded, and brushy areas is key.
    • Insect Sting Allergies
      • The majority of stinging insects in the United States are from Bees, Yellow Jackets, Hornets, Wasps and Fire Ants. Severity of reactions to stings varies greatly. Avoidance and prompt treatment are essential. In selected cases, allergy injection therapy is highly effective.
    • Indoor Allergens
      • Common sources of indoor allergens include dust mites, cockroaches, molds, pets, and plants. Managing allergies caused by indoor allergens means reducing your exposure to them.
    • See All Related Diseases & Conditions »
  • Medications

  • Procedures & Tests

  • Pictures, Images & Illustrations

  • Doctor's & Expert's Views

  • Health News

  • Health Features

Allergies & Asthma

Improve treatments & prevent attacks.



Symptom Checker: Your Guide to Symptoms & Signs: Pinpoint Your Pain









Use Pill Finder Find it Now

Pill Identifier on RxList

  • quick,
    easy,
    pill identification

Find a Local Pharmacy

  • including
    24 hour
    pharmacies