An allergy is an abnormal reaction to an ordinarily harmless substance called an allergen. When an allergen, such as pollen, is absorbed into the body of an allergic person, that person’s immune system views the allergen as an invader and a chain reaction is initiated. White blood cells of the immune system produce IgE antibodies. These antibodies attach themselves to special cells called mast cells, causing a release of potent chemicals such as histamine. These chemicals cause symptoms such as a runny nose, watery eyes, itching and sneezing.

People can be allergic to one or several allergens. The most common include pollens, molds, dust mites, animal dander (dead skin flakes from animals with fur); foods; medications; cockroach droppings and insect stings.

Allergic individuals can exhibit a variety of reactions depending on the allergen and the way it was absorbed into the body.

1. Seasonal allergic rhinitis sometimes called "hay fever" is caused by an allergy to the pollen of trees, grasses, weeds or mold spores. Depending on what you are allergic to, the section of the country and the pollination periods, seasonal allergic rhinitis may occur in the spring, summer or fall and may last until the first frost. The sufferer has spells of sneezing, itching and watery eyes, runny nose, burning palate and throat. Seasonal allergies also can trigger asthma.
2. Allergic rhinitis is a general term used to apply to anyone who has symptoms of nasal congestion, sneezing and a runny nose due to allergies. This may be a seasonal problem as with hay fever, or it may be a year-round problem caused by indoor allergens such as dust mite droppings, animal dander, cockroach droppings or indoor molds/mildew. Frequently, this problem is complicated by sinusitis. Patients with constant nasal symptoms should consult their allergist.
3. Eczema or atopic dermatitis is a non-contagious, itchy rash that often occurs on the hands, arms, legs and neck, although it can cover the entire body. This condition is frequently associated with allergies, and substances to which a person is sensitive may aggravate it.
4. Contact dermatitis is a reaction affecting areas of the skin which become red, itchy and inflamed after contact with allergens or irritants such as plants, cosmetics, medications, metals and chemicals.
5. Urticaria or hives are red, itchy, swollen areas of the skin that can vary in size and appear anywhere on the body. Approximately 25% of the U.S. population will experience an episode of hives at least once in their lives. Most common are acute cases of hives, where the cause is readily identifiable as a reaction to a viral infection, medication, food or latex. Some people have chronic hives that occur almost daily for months to years, with no identifiable trigger. Angioedema is a swelling of the deeper layers of the skin. It is not red or itchy, and most often occurs in soft tissue, such as the eyelids or mouth. Hives and angioedema may appear together or separately on the body.

Immunotherapy, or "allergy shots", is recommended for patients with moderate to severe allergy symptoms throughout most of the year, who do not respond adequately to medications, and whose symptoms are triggered by an allergen that is not easily avoided, such as pollens or house dust mites. Immunotherapy involves the injection of allergenic extracts (tiny amounts of allergens) that are given over a period of 3-5 years. By gradually increasing the amount of extract, tolerance to the offending allergen will increase, and the patient’s symptoms will be relieved.

Currently, immunotherapy is used to treat patients who are sensitive to inhaled allergens—pollens, molds, dander and house dust. Studies have also found immunotherapy to be extremely effective in many cases of stinging insect allergy as well. Immunotherapy for food allergies is not recommended because of the chance of a severe allergic reaction to the injection.

People with allergies have an inherited, genetic tendency to produce IgE, the allergic antibody, to many different substances such as seasonal allergens, (trees, grasses, weeds) or year-round allergens (dust mites, pet dander). When a person with allergies moves to another location, exposure to different allergens in the new location will likely result in a new set of allergy triggers, thereby trading one set of symptoms for another. In some cases, the benefits of a change in location may outweigh the negative aspects.

Before making a move to "get away from your allergies" consult with your allergist. Also, when contemplating a move, if possible, check out the new environment by visiting there for two to four weeks (or more) to see if your symptoms improve. Keep in mind it may take months or years to become allergic to a new allergen i.e., tree, grass or weed species.

Seasonal allergy sufferers may be able to find temporary relief by taking a vacation during the height of the pollen season to a more pollen-free environment such as near large bodies of water.

The American Academy of Allergy, Asthma and Immunology has a network of pollen counters across the United States. Each counter works under the direction of an AAAAI member and must first pass a certification course provided through the AAAAI. Counters use air sampling equipment to capture air-borne pollens. The number of pollen grains collected are then counted and logged.

There are hundreds of thousands of types of molds. All are fungi, which means they are many-celled organisms that reproduce by sending tiny seeds called spores into the air. Molds need four things to grow: food, air, the right temperature and water. Although fungi grow naturally “outdoors", molds are very common in buildings and homes and will grow anywhere indoors where there is sufficient moisture. They like dark, damp, warm environments, and can grow on anything from basement walls to garbage pails to houseplants, and many building materials. Moisture can come from water damage, excessive humidity, water leaks, condensation, water infiltration, flooding, leaking roofs, leaky plumbing, sewer backups, and frequently overflowing washing machines.

Mold and its spores contain allergens, meaning that in some people sensitivity to fungi (molds) can cause allergic reactions such as allergic rhinitis or asthma. Certain molds can cause infection, in the same way bacteria do. Molds may also produce musty odors known as volatile organic compounds that may cause irritation to the eyes, nose and throat.

Stachybotrys chartarum (also known by its synonym Stachybotrys atra) is a slow growing, greenish-black mold that needs an environment of constant moisture. It grows only on wood, paper and cotton products and can be found in 2% to 5% of American homes. Under specific environmental conditions, Stachybotrys chartarum may produce several toxic chemicals called mycotoxins. These chemicals can be present in spores and small fungus fragments released into the air, but there is currently no evidence that these small levels of exposure are harmful to humans.

If Stachybotrys chartarum spores are released into the air, there is a potential for humans to develop symptoms such as coughing, wheezing, runny nose, irritated eyes or throat, particularly if the person has developed an allergy to this fungus. Stachybotrys chartarum has been blamed for pulmonary hemosiderosis (bleeding in the lungs) in a small number of infants. However, experts claim that this is “not proved”. Other factors such as second-hand tobacco smoke may be more important.