Considering the amount of time most people spend in their home and at work, it is very important that these environments be kept relatively free of allergens. People suffering from airborne allergies or asthma are often plagued by the presence of these substances.

The most common types of indoor allergens include:

• Dust and dust mites
• Animal dander
• Cockroach debris
• Mold

Because of their tiny size, indoor allergens can easily become airborne. While many types of indoor allergens settle onto surfaces when the air is still, they are often stirred up into the air once disturbed. This can occur when a person is cleaning, opening a door or simply walking through a room. Once allergens are in the air they are easily inhaled. Oftentimes, airborne allergens are spread throughout the house via an air conditioning system.

Indoor allergens include a type of protein that triggers an allergic reaction when inhaled by a sensitive individual. The protein is mistakenly perceived as a threat by the immune system, which responds by releasing chemicals into the blood. These chemicals cause allergy symptoms including runny nose, coughing, sneezing, itchy eyes and nasal congestion.

People with allergies that trigger asthma-like symptoms, or those who have allergic asthma, can have an asthma attack after inhaling an indoor allergen. Airborne allergens can disturb or irritate the sensitive muscles in an asthmatic person's airways, causing those muscles to constrict. This can lead to shortness of breath or difficulty breathing.

In order to determine if a patient is sensitive to indoor allergens, a physician will conduct a physical examination and compile the patient's medical history, including a list of symptoms. In addition, an allergy skin test or blood test may be performed.

While indoor allergens are not usually seasonal like many types of outdoor allergens, late summer usually sees higher levels of dust mites (due to higher humidity), molds and some pollens (which can be tracked indoors or brought in on clothes).

These circumstances can cause some people to experience more severe indoor allergy symptoms in summer. However, cold temperatures in the winter are often responsible for keeping people shut inside for long periods of time. This has the effect of both increasing the amount of exposure an individual has to indoor allergens, and raising the amount of allergens in the home due to the decreased ventilation. Most houses are closed tight during winter.

Research also suggests that indoor allergen levels vary throughout the United States. A recent study found that people in the Northeast and areas of the Midwest had the highest exposure and sensitivity levels to cockroach debris. Dust mite allergens, on the other hand, were most prominent in the South and Northwest.

Some buildings have ongoing indoor air quality problems as a result of poor building design or occupant activities. This is called sick building syndrome (SBS). Chemical contaminants, inadequate ventilation and biological contaminants (e.g., molds, pollens) are factors that are commonly associated with SBS. People who suffer from indoor allergies may find their condition aggravated if living or working in a building with SBS.