Allergy medications work by blocking the action of histamine, a chemical that's released by the body in response to an allergen. Antihistamines, such as loratadine and cetirizine, are commonly used to relieve allergy symptoms like sneezing, itching, and runny nose. Decongestants, like pseudoephedrine, can also help to relieve nasal congestion. In severe cases, corticosteroids may be prescribed to reduce inflammation.