Indoor allergens are biological or chemical substances that trigger the immune system, causing an allergic reaction. Biological sources of allergens include pets, insects, dust mites, plants, bacteria, and mold. Chemical sources are often gases or particles released by items such as building materials, fabrics, glues, paints, solvents, dyes, and perfumes. The most common way to be exposed to indoor allergens is by breathing them. Exposures can also occur if allergens are ingested, or if they come into contact with the skin or eyes.
All buildings contain indoor allergens because there are so many different sources.
For instance, pet hair, dust mites, cockroaches, and mold are common sources of indoor allergens. Outdoor plants can contribute to indoor allergens by releasing pollen that then enters buildings. Hay fever is an allergic response to grass pollen. Chemicals can also act as allergens. Metals, perfumes, dyes, and solvents found in common household products such as carpet, upholstery, laundry detergents, and paints can cause symptoms in people.