Home > Allergy > What is an Allergy? Get the Flash Player to see this player. Rate: (Click the stars to rate) Published on Dec 15, 2008 by JamesLi, Views: 5130 This animated video shows you the common allergens, how they cause a reaction in your body, and how the treatment for allergies works. Common allergens are pollen, animal dander, down feathers, mites, chemicals, and foods. Antihistamines can block the symptoms of allergy such as coughing, sneezing, runny nose, and watery eyes.