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Allergy Basics

About Dr  Sohail Asghar Roomi

What Are Allergies? 
Allergies are a very common problem, affecting at least 2 out of every 10 Americans. 
Allergies are an overreaction of the immune system. People who have allergies have a hyperalert immune system that overreacts to a substance in the environment called an allergen. Exposure to what is normally a harmless substance, such as pollen, causes the immune system to react as if the substance is harmful. 

What Happens During an Allergic Reaction? 
When a person who has this hyperalert immune system is exposed to an allergen a series of events takes place: The body starts to produce a specific type of antibody called IgE to fight the allergen. 
The antibodies attach to a form of blood cell called a mast cell. Mast cells are plentiful in the airways, and in the GI tract where allergens tend to enter the body. 
The mast cells explode releasing a variety of chemicals including histamine, which causes most of the symptoms of an allergy including itchiness or a runny nose. 
If the allergen is in the air, the allergic reaction will occur in the eyes, nose, and lungs. If the allergen is ingested, the allergic reaction will occur in the mouth, stomach, and intestines. Sometimes enough chemicals are released from the mast cells to cause a reaction throughout the body, such as hives, decreased blood pressure, shock or loss of consciousness. This severe type of reaction is called anaphylaxis and may be life-threatening. 

What Are the Symptoms of Allergies? 
Allergy symptoms can be categorized as mild, moderate, or severe (anaphylactic). 
Mild reactions include those symptoms that affect a specific area of the body such as a rash or hives, itchy, watery eyes, and some congestion. Mild reactions do not spread to other parts of the body. 
Moderate reactions include symptoms that spread to other parts of the body. These may include itchiness or difficulty breathing. 
A severe reaction (anaphylaxis) is a rare, life-threatening emergency in which the body's response to the allergen is sudden and affects the whole body. It may begin with the sudden onset of itching of the eyes or face and within minutes progress to more serious symptoms, including varying degrees of swelling as in hives (if the airways or throat are involved in the swelling, this could result in difficulty swallowing and breathing), abdominal pain, cramps, vomiting, and diarrhea. Mental confusion or dizziness may also be symptoms, since anaphylaxis causes a quick drop in blood pressure. 

Does Everyone Have Allergies? 
No. Most allergies are inherited, which means they are passed on to children by their parents. People inherit a tendency to be allergic, although not to any specific allergen. When one parent is allergic, their child has a 50% chance of having allergies. That risk jumps to 75% if both parents have allergies. 

Types of Allergies 
What Are the Common Types of Allergies? 
People can be allergic to a variety of substances, the most common of which are pollen and dust mites. 
Pollen: Allergic rhinitis, or hay fever, is an allergy to pollen. It causes inflammation and swelling of the lining of the nose, as well as the lining of the eyes and eyelids (conjunctiva). Symptoms include sneezing, congestion and itchy, watery eyes. Treatments include over-the-counter and prescription antihistamines such as Benadryl, nasal steroids, and nasal cromolyn. Prevent pollen exposure by staying indoors when pollen counts are high, closing windows and using air conditioning. 
Dust mites: These are microscopic organisms that live in dust. House dust is a mixture of potentially allergenic materials including fibers from different fabrics, dander from animals, bacteria, mold or fungus spores, food particles, bits of plants or other allergens. Symptoms are similar to those for pollen allergy and can also produce symptoms of asthma such as wheezing and coughing. Treatments include medications such as antihistamines or decongestants. Immunotherapy may be recommended for people whose symptoms are chronic. 
Molds: These are parasitic, microscopic fungi with spores that float in the air like pollen. Mold is a common trigger for allergies and can be found in damp areas such as the basement or bathroom, as well as in grass, leaf piles, hay, mulch or under mushrooms. In some people, symptoms of mold allergy may be brought on or made worse by eating certain foods, such as cheese processed with fungi. Symptoms include sneezing, congestion, itchy, watery eyes, runny nose and coughing. Treatment with antihistamines or corticosteroids is usually helpful, but avoiding these substances is important also. 
Animal dander: Proteins secreted by oil glands in an animal's skin, as well as the proteins present in an animal's saliva, cause allergic reactions in some people. Allergies to animals can take two or more years to develop and symptoms may not subside until months after ending contact with the animal. Symptoms include sneezing, congestion and itchy, watery eyes. Treatments include avoiding exposure to the animals causing your allergies if possible. Medications such as antihistamines or decongestants may be helpful, or immunotherapy may be recommended if your symptoms are chronic. 

What Other Allergies Are There? 
Latex: Latex allergy develops after some sensitizing contact with latex. Rubber gloves are the main source of allergic reactions. 
A component of the latex substance itself is an allergen for many people. The latex glove powder is an airborne allergen, which causes upper airway allergic reactions in some people, as well as worsening asthma. Symptoms include skin rash, hives, eye tearing and irritation, wheezing and itching of the skin. Allergic reactions to latex can range from skin redness and itching to much more serious symptoms such as difficulty breathing, hives, or acute (sudden-onset) gastrointestinal problems. Treatments include removal of the latex product and drugs according to the type of symptoms developing. If you have latex allergy, it is important for you to wear a MedicAlert bracelet and carry an emergency epinephrine kit at all times. There is no cure for latex allergy, so the best treatment is prevention. 
Foods: Food allergies develop when there is an IgE antibody to a specific food. An allergic reaction occurs within minutes of eating the food and symptoms can be severe. Milk, fish and shellfish, nuts, peanuts, wheat and eggs are the most common foods that cause allergies. Non-allergic food intolerance is more common than true food allergy. Symptoms include asthma (wheezing and coughing), hives, runny nose, vomiting, diarrhea, and swelling in the area around the mouth. The best treatment is to avoid the foods that cause allergy symptoms. For rashes, skin creams may ease discomfort, while antihistamines will help reduce itching, congestion, and other symptoms. For more serious reactions, corticosteroids such as prednisone will help to reduce swelling. In life-threatening situations, an epinephrine (adrenaline) injection immediately begins reversing symptoms and is the only effective treatment option. 
Insect stings: Everyone who gets stung by an insect will have pain, swelling, and redness around the sting site. However, some people are allergic to stings and have severe or even life-threatening reactions. Symptoms include difficulty breathing; hives that appear as a red, itchy rash that spreads to areas other than the immediate area stung; swelling of the face, throat or mouth; wheezing or difficulty swallowing; restlessness and anxiety; rapid pulse; dizziness or a sharp drop in blood pressure. You may take an oral antihistamine, like Benadryl, to reduce itching, swelling, and hives. To relieve pain, take aspirin or an aspirin 
substitute. An allergic reaction is treated with epinephrine (adrenaline), either self-injected or administered by a doctor. Usually this injection will stop the development of severe allergic reaction.

Frequently Asked Questions about Allergies 
Print out these questions and answers to discuss with your doctor. 

What types of plants produce the most allergenic pollen? 
The type of pollen that most commonly causes allergic reactions comes from plants (trees, grasses and weeds) which typically do not bear fruit or flowers. These plants produce small, light, dry pollen granules in large quantities that can be carried through the air for miles. 

Common allergenic culprits include: 
Weeds such as ragweed (including the marsh-elder, desert broom, feverfew, dog fennel, chamomile, chrysanthemum and marigold families), sagebrush, redroot pigweed, lamb's quarters, goosefoot, tumbleweed (Russian thistle) and English plantain. 
Grasses such as timothy grass, Kentucky blue grass, Johnson grass, Bermuda grass, redtop grass, orchard grass, sweet vernal grass, perennial rye, salt grass, velvet grass and fescue. 
Hardwood deciduous trees such as oak, ash, elm, birch, maple, alder and hazel as well as hickory, pecan, box and mountain cedar. Juniper, cedar, cypress, and sequoia trees are also likely to cause allergies. 

What does a pollen count mean? 
A pollen count is the measure of the amount of pollen in the air. Pollen counts are commonly included in local weather reports. 
The counts are usually reported for mold spores and three types of pollen: grasses, trees and weeds. The count is reported as grains of pollen per square meter of air collected over 24 hours. This number represents the concentration of all the pollen in the air in a certain area at a specific time. The pollen count is translated into a corresponding level: absent, low, medium or high. 

In general, a "low" pollen count means that only people extremely sensitive to pollen will experience symptoms. A "medium" count means many people who are sensitive to pollen will experience symptoms, and a "high" count means most people with any sensitivity to pollen will experience symptoms. 

Although the pollen count is approximate and fluctuates, it is useful as a general guide when you are trying to determine whether or not you should stay indoors to avoid pollen contact. 

Should I consider moving to decrease my allergy symptoms? 
No. It is a fallacy that moving to a different geographic climate will help "cure" allergies. Most people who relocate to get away from pollens that cause their allergies tend to find that they eventually develop allergies to the plant pollens in the new area. 
Other airborne allergens, such as dust or mold, may also cause symptoms in some people. 

How can I tell if my son has allergies or just a common cold? 
Symptoms of allergies and colds can be similar, but here's how to tell the difference: 
Occurrence of symptoms: Both allergies and colds cause symptoms of sneezing, congestion, runny nose, watery eyes, fatigue and headaches. However, colds often cause symptoms one at a time: first sneezing, then a runny nose and congestion. Allergies cause symptoms that occur all at once. 

Duration of symptoms: Cold symptoms generally last 7 to 10 days, whereas allergy symptoms continue with exposure to the allergen (symptom trigger). Allergy symptoms may subside soon after elimination of allergen exposure. 

Mucus discharge: Colds may cause yellowish nasal discharge, suggesting an infectious cause. Allergies generally cause clear, thin, watery mucus discharge. 

Sneezing: A more common symptom of allergies, especially when sneezing two or three times in a row. 

Time of year: Colds are more common during the winter months, whereas allergies are more common in the spring through the fall, when trees, plants and grasses are pollinating. 

Presence of a fever: Colds may be accompanied by a fever, but allergies are not usually associated with a fever. 


Reviewed by the doctors at The Cleveland Clinic Department of Allergy and Immunology and the Department of Pulmonary and Critical Medicine. 
Reviewed by Charlotte E. Grayson, MD, WebMD, March 2002.