In Ayurveda there are two categories of allergen reactions. One is the type that a person is born with, caused by genetic predisposition. It can be a reaction to certain foods or to certain allergens in the environment such as dust and pet dander. Second category includes seasonal reactions, or sensitivities that a person has acquired later in life.
Antihistamines work by preventing more histamine (a chemical released during an allergic reaction) from being released. Another option is the medication Singular, also used to treat asthma, which works by blocking leukotrienes, substances which help cause Allergy symptoms.