Allergy-related symptoms can occur after you are around mold, certain animals or animal hair, dust, and other substances. These substances are usually found indoors and do not cause symptoms for most people.

See also:

• Asthma
• Allergic rhinitis

Allergies are relatively common. They are caused by an over-sensitive immune response. The immune system normally protects the body against harmful substances such as bacteria and viruses. Allergy occurs when the immune system reacts to substances (allergens) that are generally harmless and, in most people, do not cause an immune response.

When a person with allergies breathes in an allergen, histamine and other chemicals are released as part of the immune response. This causes itching and swelling, mucus production, and in serious cases, hives and rashes, as well as other symptoms.

Symptoms vary in severity from person to person. Most environmental allergens contact the skin or eyes, or are inhaled. Therefore, most symptoms affect the skin, eyes, or the breathing passages.

You may develop an allergic reaction to particles in the indoor or outdoor environment that leads to hay fever-like symptoms. Common allergy triggers include:

• Mold -- Mold spores are carried in the air and may be present all year long. Mold is most common indoors in damp locations such as basements, bathrooms, or washrooms. Fabrics, rugs, stuffed animals, books, or wallpaper can contain mold spores if they are frequently in contact with water or kept in a damp place. Outdoors, mold lives in the soil, on compost, and on damp vegetation.
• Animals -- People who are allergic to certain animals are rarely allergic to the animals' fur or feathers. They are actually allergic to the small scales of skin (dander) that the animal sheds. Some people are allergic to the animal's saliva, particularly cats. Cats have saliva that contains a protein known to cause allergy. You can come into contact with animal saliva if the pet licks you, if you touched the pet after it has groomed itself, or if you touch an object that the animal has recently licked or chewed.
• Dust -- House dust contains tiny particles of pollen, mold, fibers from clothing and fabrics, detergents, and microscopic insects (mites). Dust mites, including small fragments of dead mites, are the primary cause of dust allergy and are found in the highest numbers in bedding, mattresses, and box springs.

A few people develop allergy-like symptoms to other irritants in the environment, including smoke, fumes from industries or cleaning products, tobacco, powder, and laundry detergents.

• Coughing
• Difficulty breathing
• Hives
• Itching of the nose, eyes, throat, or skin
• Rash
• Redness in the eyes
• Runny nose
• Sinus pressure
• Sneezing
• Tearing eyes
• Wheezing

The doctor will perform a physical exam and ask you questions about your symptoms. The history of symptoms is important in diagnosing allergies, including whether the symptoms vary according to time of day or the season and possible exposures such as having a pet in the household.

Allergy testing is done to see identify the specific allergens that are causing your symptoms. Skin testing is the most common and useful method. This may include scratch, patch, or other tests.

If your doctor determines that you cannot undergo skin testing, a RAST blood test (to look for IgE antibodies to a specific allergen) may be helpful.

Having allergies may also alter the results of the following tests:

• WBC count, particularly eosinophil count
• Serum immunoelectrophoresis

The goal of treating allergic rhinitis is to reduce allergy symptoms caused by the inflammation of affected tissues.

The best "treatment" is to avoid what causes the allergic symptoms in the first place. It may be impossible to completely avoid all allergens to which you are sensitive, but you can often take steps to reduce exposure.

Medication options include the following:

• Short-acting antihistamines can relieve mild to moderate symptoms, but can cause drowsiness. Many may be bought without a prescription. A pediatrician should be consulted before using these medicines in children, as they may affect learning. Loratadine (Claritin) is now available over the counter. It does not tend to cause drowsiness or affect learning in children.
• Longer-acting antihistamines are available by prescription. They cause less drowsiness and can work just as well. They usually do not interfere with learning. These medications include fexofenadine (Allegra), and cetirizine (Zyrtec).
• Nasal corticosteroid sprays work very well for people with symptoms not relieved by antihistamines alone. These prescription medications include fluticasone (Flonase), mometasone (Nasonex), and triamcinolone (Nasacort).
• Azelastine (Astelin) is a new, nasal antihistamine that is used to treat allergic rhinitis.
• Decongestants may also be helpful in reducing symptoms such as nasal congestion, but should not be used for long periods.
• Cromolyn sodium is available as a nasal spray (Nasalcrom) for treating hay fever. Eye drop versions of cromolyn sodium and antihistamines are available for itchy or bloodshot eyes.
• The leukotriene inhibitor montelukast (Singulair) is a prescription medicine approved to help control asthma and to help relieve the symptoms of seasonal allergies.

The most appropriate medication depends on the type and severity of symptoms. Specific illnesses that are caused by allergies (such as asthma and eczema) may require other treatments.

Allergy shots (immunotherapy) are occasionally recommended if the allergen cannot be avoided and symptoms are hard to control. Immunotherapy includes regular injections of the allergen, given in increasing doses (each dose is slightly larger than the previous dose) that may help the body adjust to the antigen. As mold, animal, and dust avoidance are more feasible than avoiding outdoor pollens, allergy shots are less commonly prescribed for these types of allergies.

Most symptoms of allergies to mold, dander, and dust can be readily treated, and regular treatment can minimize the symptoms.

In some cases (particularly in children), people may outgrow an allergy as the immune system becomes less sensitive to the allergen. However, as a general rule, once a substance causes allergies for an individual, it can continue to affect the person long term.

The most severe cases of allergic rhinitis from these allergens may require immunotherapy (allergy shots) or removal of tissue in the nose or sinuses.

• Frequent ear infections (otitis media) in children
• Drowsiness and other side effects of antihistamines
• Side effects of other medications (see the specific medication)
• Sinusitis
• Nasal polyps
• Hives or other skin rashes
• Anaphylaxis (a rare but severe allergic reaction)
• Disruption of lifestyle

Call your health care provider if severe symptoms of allergy occur, if previously successful treatment has become ineffective, or if symptoms do not respond to treatment.

There is no known way to prevent development of allergies, but recent research has given us clues.

Breastfeeding can be effective at preventing and decreasing allergies. There is also evidence that exposures to certain allergens in the first year of life may prevent some allergies. This is called the "hygiene hypothesis" and sprang from observations that infants on farms tend to have fewer allergies than those in environments that are more sterile. Once allergies have developed, avoiding known allergens may decrease symptoms and prevent other allergies.

Mold spores are everywhere. Minimize exposure by keeping rooms dry, using a dehumidifier if necessary. Discard moldy or mildewed articles (books, toys, shoes, and so on). Use synthetic fabrics for clothing and household furnishings whenever possible. Disinfect bathrooms, basement walls, and furniture with diluted bleach or other appropriate disinfectant solution.

Clean frequently to minimize dust. Vacuum frequently, preferably using a small-pore filter to capture dust mites. Damp-mop and dust often. Eliminate as many "dust catchers" as possible, including rugs, bed ruffles or canopies, and curtains. Bedding and mattresses harbor dust mites.

You can buy special covers for mattresses, box springs, and pillows to reduce dust mite allergens. Wash rugs, bedding, and furniture coverings weekly if possible. Central heating and air-conditioning systems may be helpful, particularly if they include special filters to capture dust.

People who are allergic to animals may need to avoid keeping pets. Frequent bathing and grooming of the pet (preferably by someone who is not allergic to the animal) may help. Allergy to animals may also include wool, which may contain tiny amounts of dander (skin).

Avoid other irritants whenever possible.