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Did you know that you could be sharing your bed with anywhere from 100,000 to 10 million dust mites? These microscopic organisms, which are related to spiders, live in many homes. Too small to see with the naked eye, dust mites thrive in warm, humid environments — eating dead skin cells and nesting in dust-collecting bedding, fabric, carpet and furnishings.

The residue that dust mites leave behind in the form of their feces and decaying bodies mixes with dust and becomes airborne. If you aren't allergic to dust mite residue, it's not harmful. But if you are, inhaling the residue can cause bothersome allergy symptoms, including wheezing, sneezing, watery eyes and runny nose.

One treatment for dust mite allergy is avoidance — that is, taking measures to minimize the number of dust mites in your home. Your doctor may also recommend allergy medications or allergy injections.

If you have a dust mite allergy, you may exhibit the signs and symptoms of hay fever (allergic rhinitis). Dust mite allergy symptoms may include:

• Sneezing
• Runny nose
• Itchy, watery eyes
• Nasal congestion
• Itchy nose, roof of mouth or throat
• Swollen, blue-colored skin under your eyes
• Postnasal drip
• Cough
• Irritability
• Facial pressure and pain

If you have asthma, you may also experience increased signs and symptoms of asthma, such as:

• Lung congestion
• Wheezing
• Shortness of breath

You may be especially prone to asthma attacks at night, when sleeping in a bed infested with dust mites.

A dust mite allergy can range from mild to severe. A mild case of dust mite allergy may result in an occasional runny nose, watery eyes and sneezing. In severe cases, the condition is chronic — resulting in, for example, persistent wheezing, sneezing, congestion and facial pressure.

As dust mites multiply, so does the residue made up of their feces and decaying bodies. If you're sensitive to dust mites, your body reacts when inhaling this residue.

During a process called sensitization, your immune system mistakenly identifies the inhaled dust mite residue as an invader and produces an antibody against it called immunoglobulin E (IgE).

The next time you're exposed to the dust mite residue, your immune system launches an allergic reaction. The IgE antibodies trigger the release of an inflammatory chemical called histamine, which causes swelling of the mucous membranes in your lungs, nose, sinuses and eyes that results in wheezing, runny nose, sneezing and watery eyes.

The following factors increase your risk of developing a dust mite allergy:

• Heredity. You're more likely to develop a sensitivity to dust mites if dust mite allergies run in your family.
• Exposure. Being exposed to high levels of dust mites, especially early in life, increases your risk.
• Age. You're more likely to develop allergy symptoms during childhood or early adulthood.

If you experience signs and symptoms, such as wheezing, shortness of breath, sneezing, runny nose and watery eyes, and you suspect dust mites or another allergen are to blame, see your doctor for an evaluation. Allergy skin tests — which expose your skin to purified extracts of allergy-causing substances — can help your doctor determine whether you have a dust mite allergy.

If you experience persistent wheezing, sneezing, watery eyes and runny nose, your doctor will likely recommend a puncture, prick or scratch skin test to determine whether your signs and symptoms are caused by an allergy.

In this test, tiny drops of purified allergen extracts — including an extract for dust mites — are pricked or scratched into your skin's surface. This is usually carried out on the forearm, though it may be done on the upper back in children.

Your doctor or nurse will clean the test site with alcohol, then use a sharp instrument (lancet) to introduce individual extracts into your skin's surface. This causes only little, if any, discomfort.

The drops are left on your skin for 15 minutes before your doctor or nurse observes your skin for signs of allergic reactions. If you're allergic to dust mites, you'll develop a red, itchy bump where the dust mite extract was scratched onto your skin.

The most common side effect of these skin tests is itching and redness. This usually subsides within a few hours, although it can persist until the next day.

Your doctor may also recommend allergy blood tests, especially if the allergy skin tests can't be completed.

You're more likely to develop asthma — a condition in which the main air passages of your lungs (bronchial tubes) become inflamed and your airways become narrowed — if you're already sensitive to environmental allergens, including dust mites.

If you already have asthma, dust mite allergy or exposure to dust mites can cause an increase in asthma signs and symptoms, including shortness of breath, wheezing and coughing. For this reason, taking measures to decrease the number of dust mites in your home can improve control of asthma.

The most effective treatment for avoiding an allergic reaction to dust mites is avoidance. When you minimize your exposure to dust mites, you'll also minimize the signs and symptoms of an allergic reaction — such as watery eyes, runny nose and sneezing. Adopting rigorous cleaning practices, especially in your bedroom, can help reduce dust mite residue to a level where it no longer causes bothersome problems.

Medications
When you can't control your allergic reactions to dust mites with prevention measures, your doctor may recommend or prescribe allergy medications. For allergic rhinitis, these may include:

• Nonprescription medications. To counter the signs and symptoms of allergy-induced hay fever, short-acting antihistamines (Benadryl, Claritin, others), decongestants (Sudafed, Chlor-Trimeton, others) or a nasal spray containing cromolyn sodium (NasalCrom) may help.
• Prescription hay fever medications. These include longer acting antihistamines (Zyrtec, Clarinex, others), nasal corticosteroid sprays (Flonase, Nasonex, others) to reduce inflammation, and the leukotriene inhibitor montelukast (Singulair), which blocks the action of leukotrienes — immune system chemicals that cause allergy signs and symptoms, such as excess mucus production.

If your dust mite allergy is causing asthma symptoms, your doctor may prescribe inhaled corticosteroids (Flovent, Pulmicort, others), long-acting beta-2 agonists (Serevent, Foradil), combination inhaled corticosteroids plus long-acting bronchodilators (Advair), and short-acting beta-2 agonists (albuterol, others), which help open up the airways in your lungs.

Immunotherapy
If your symptoms are especially difficult to control or are causing troublesome nose, eye or asthma symptoms, your doctor may recommend allergy shots (immunotherapy) to desensitize you to dust mites.

In immunotherapy, you'll receive injections of dust mite extract in increasing doses once or twice a week. Once a maintenance dose has been reached, you'll need injections every four weeks.

Avoiding exposure to dust mites can minimize your risk of allergic reactions. While you can't completely eliminate dust mites from your home, you can significantly reduce their number. Use these suggestions:

• Build a barrier. Cover your mattress and pillows in dust-proof or allergen-impermeable covers.
• Maintain low humidity in your home. Aim for 30 percent to 50 percent relative humidity. A dehumidifier or air conditioner can help keep humidity low, while a hygrometer (available at hardware stores) can measure humidity levels.
• Choose bedding wisely. Use synthetic materials as opposed to wool or down bedcovers.
• Buy washable stuffed toys. Wash them often in hot water and dry thoroughly. Also keep stuffed toys off beds.
• Wash bedding weekly. Kill dust mites by washing all sheets, blankets, pillowcases and bedcovers in hot water (130 to 140 F). Freeze nonwashable bedding overnight in a chest freezer.
• Remove dust. Use a damp mop or rag instead of a dry cloth.
• Vacuum regularly. Use a vacuum cleaner with a double-layered microfilter bag or a high-efficiency particulate air (HEPA) filter. Vacuum both carpet and fabric-covered furniture. If your allergies are severe, leave the area being vacuumed while someone else does the dirty work. Stay out of the vacuumed room for 20 minutes after vacuuming.
• Cut clutter. If it collects dust, it also collects dust mites. So remove knickknacks, tabletop ornaments, books, magazines and newspapers from your bedroom.
• Rethink flooring. If your dust mite allergy is severe, replace your wall-to-wall bedroom carpet with tile, wood or linoleum flooring. Also consider replacing upholstered furniture and removing fabric curtains.

Though you may be tempted to purchase an air purifier to lessen the symptoms of your dust mite allergy, you should know that air purifiers alone aren't effective for reducing dust mites. This is because dust mites aren't airborne for long periods. When they are sent into the air, they don't stay long; they're too heavy. Vigorous cleaning practices, along with the other tips above, are better bets for minimizing dust mites in your home. For some people, adding an air purifier to the steps described above can reduce the amount of airborne dust.