What's Behind the Symptoms?
Allergies are the result of an exaggerated immune response to an agent, or allergen, that's not really dangerous but is treated as such by the body's defenses. Allergies are closely related to atopic dermatitis and asthma, two other conditions in which the immune system overreacts to a harmless trigger.
The term allergies applies to several distinct diseases, all with their own symptoms and treatments. However, they have a common underlying cause: a hypersensitivity to otherwise benign things. Some of the most common allergic conditions are:
Allergic rhinitis, also known as hay fever or nasal allergies
Allergic asthma, a type of asthma triggered by an allergic reaction
Insect bite/sting allergies
Eye allergies, also known as allergic conjunctivitis
Some herbs used to treat allergies and asthma can cause allergic reactions themselves in sensitive individuals. Anyone who's allergic to plants in the Asteraceae/Compositae family, which include ragweed and daisies, should avoid remedies made with other family members, such as arnica (Arnica montana), butterbur (Petasites hybridus), calendula (Calendula officinalis), chamomile (Matricaria recutita), echinacea (Echinacea purpurea), and yarrow (Achillea millefolium).
Some of these conditions overlap: Food allergies can trigger an allergic reaction in the skin as well as in the digestive tract, for example, and inhaled irritants that can trigger an episode of allergic rhinitis might also bring on allergic asthma.