Causes of Allergy:

Any allergy starts when your immune system mistakes a harmless substance for a dangerous one. The immune system then produces antibodies that remain on the alert for that particular allergen. When you're exposed to the allergen again, these antibodies can release a number of immune system chemicals that cause allergy symptoms. 

Common allergy triggers include:·      

Airborne allergens, such as pollen, animal dander, dust mites andmold·      

Certain foods, particularly peanuts, tree nuts, wheat, soy, fish, shellfish, eggs, and milk·      

Insect stings, such as from a bee or wasp·      

Medications, particularly penicillin or penicillin-based antibiotics·      

Latex or other substances you touch, which can cause allergic skin reactions