Cause of Environmental Allergies
Both genetic and environmental factors can contribute to the development of allergies. Allergic rhinitis (hay fever) and asthma are triggered by exposure to airborne allergens. Sources of allergens include pollens, pet dander, house dust mites, molds, cockroaches, and rodents.
Each spring, summer, and fall, plants release tiny pollen grains to fertilize other plants of the same species. People with allergic rhinitis or asthma aggravated by pollen have symptoms only for the period or season when the pollen grains to which they are allergic are in the air.
However, not all seasonal symptoms are due to pollen. Rhinovirus, the cause of the common cold, causes runny noses and triggers asthma attacks in the fall and spring. Most of the pollens that generate allergic reactions come from trees, weeds, and grasses. These plants make small, light, and dry pollen grains that are carried by wind.
Molds are found both indoors and outdoors. Outdoor molds are carried by the wind, like pollens. There are many different types of molds, but only some seem to cause health problems. High levels of the mold Alternaria have been associated with severe asthma spergillus, another type of mold, is associated with a severe and chronic form of asthma.
Indoor molds may cause allergy as well as other health effects. Some people report not feeling well when living in a moldy or damp environment, even if they do not have allergies. However, there has been little research examining the health effects of indoor molds.
Other Indoor Allergens
Allergic rhinitis and asthma also can be triggered by exposure to house dust, for example, during household chores such as vacuuming or sweeping. Dust is a mixture of substances and may contain allergens from house dust mites, pets, mold, cockroaches, and rodents.
While exposure to animals like cats and dogs can cause symptoms of allergic rhinitis and asthma in sensitive people, exposure in early life may have a protective effect.
Environmental Allergies: Symptoms
Symptoms of allergic rhinitis and asthma include the following:
- Runny nose and mucus production
- Itchy nose, eyes, ears, and mouth
- Stuffy nose
- Red and watery eyes
- Swelling around the eyes
- Chest tightness
- Shortness of breath
Environmental Allergies: Diagnosis
A healthcare professional may perform skin, blood, or allergy component tests to help diagnose environmental allergies.
A skin prick test can detect if a person is sensitive to a specific allergen. Being “sensitive” means that the immune system produces a type of antibody called IgE against that allergen. IgE attaches to specialized cells called mast cells. This happens throughout the body, including the lining of the nose and the airways, as well as the skin.
During a skin prick test, a healthcare professional uses a piece of plastic to prick the skin on the arm or back and place a tiny amount of allergen extract just below the skin’s surface. In sensitive people, the allergen binds to IgE on mast cells in the skin and causes them to release histamine and other chemicals that produce itching, redness, and minor swelling.
Healthcare professionals often will try to match skin test results with the kind of allergen exposures a person may have had.
Instead of performing a skin test, doctors may take a blood sample to measure levels of allergen-specific IgE antibodies. Most people who are sensitive to a particular allergen will have IgE antibodies detectable by both skin and blood tests.
As with skin testing, a positive blood test to an allergen does not necessarily mean that a person’s symptoms are caused by that allergen.
Allergy Component Tests
One reason why a positive skin or blood test does not always indicate that a person’s symptoms are caused by a particular allergen is that allergens comprise many different components, some of which are more likely to cause symptoms than others. Allergy component tests are blood tests that can determine exactly which component of an allergen the IgE in a person’s blood recognizes. This can help a health professional determine whether the allergen is likely to cause symptoms.