Most people with asthma or hay fever or other outdoor allergies think of their home as a haven where they can escape their allergies. Unfortunately, houses and apartment buildings harbor their own allergens (agents that cause allergy symptoms). The inside of your home actually traps allergens, making them impossible to avoid.



Although many allergens in your environment can trigger allergic symptoms, house dust is the main culprit in indoor allergies. What is house dust? It varies depending on the type and age of your home, the temperature and humidity in the home, what you keep in the home (everything from food to clothes to furniture), and who lives in the home (human, pet animal, and plant).

Some dust is present in every home, regardless of how often or how thoroughly the house is cleaned. House dust is an airborne mixture that might contain fine particles of soil and plant material from indoors or outdoors, particles of human and animal skin (dander) and hair, fabric fibers, mold spores, dust mites, fragments of insects that have died and their waste, food particles, and other debris.

Although many substances in dust can trigger allergic symptoms, the most important indoor allergens are dust mites, pet dander, cockroaches, and molds. Unlike seasonal allergies such as hay fever, indoor allergies may last all year long. Indoor allergens may provoke or worsen asthma symptoms, depending on a person's unique sensitivities.

Indoor allergies tend to be at their worst in the late summer, when dust mites are at their peaks. Allergy symptoms can actually be worse in the winter when the windows are closed and people are shut in with the allergens. Keeping your windows open at night during seasons of high outdoor pollen and mold count may worsen your allergy symptoms or asthma because these high-concentration outdoor allergens are allowed into your house to settle.

If you are sensitive to indoor allergens, you will continue to have symptoms as long as you are exposed to your allergens. Sensitivity to indoor allergens is very common and occurs at every age. It is less common in children younger than 5 years. People most likely to experience allergic rhinitis are those in early school and early adult years.

An allergic sensitivity is a reaction of the immune system to a foreign invader, a substance that is not native to your body. Exposure to this invader, an allergen, triggers the reaction.

When the allergen particles come to rest in the linings of the eyes, nose, or airway of a susceptible person, an allergic reaction can occur.

When the immune system has been previously sensitized to a specific invader, it overreacts to the invader; this overreaction to a harmless substance is known as a hypersensitivity or allergic reaction. This reaction sets in motion a series of responses that culminates in release of chemicals called mediators. Histamine is an example of a mediator.

It is the effects of the mediators on cells and tissues that cause allergic symptoms. Dust mites are common indoor allergens. They can be found in most homes, usually in beds and bedding, upholstered furniture, or any cloth material. Often, when people believe they are sensitive to dust, they are actually sensitive to the dust mites and their waste particles and fragments of dust mites that have died that can be found in household dust.