How is the cause of allergy determined?

The exaggerated response of the immune system to certain antigens present in the environment is called allergy. The substances to which such an immune response is produced are called allergens. Common examples of allergens are mites in dust, pollens, animal dander, etc. Symptoms of allergic reactions include sneezing, watery eyes, running nose and difficulty in breathing. Allergy is due to the release of chemicals like histamine and serotonin . Somehow, modern-day life style has resulted in lowering of immunity and more sensitivity to allergens . This could be because of the protected environment provided early in life.