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. An allergic reaction develops when a person who is sensitive to a particular substance, comes into contact with that substance. Exposures to an allergen can cause a runny nose, sneezing, coughing, difficulty breathing, skin rashes, and watery eyes. Severe allergic reactions can be life threatening and require immediate medical treatment. Repeated or long exposure to the allergen will often make the symptoms worse.