Alllergy is basically an exaggerated immune response to some common materials like dust, pollen, food, etc. The immune response is set up in the body to fight against injurious and harmful substances. Sometimes, mistakenly the immune system identifies some substances as dangerous and defends the body against foreign invaders. Allergies are due to these substances recognizes by body as foreign particles, known as allergens. Allergies are developed at any stage of life. The common allergic diseases are allergic rhinitis (nasal allergies), allergic asthma, and food allergies.