An allergy is the response of the body's immune system to normally harmless substances, such as pollens, foods, and house dust mite. While in most people these substances (allergens) pose no problem, in allergic individuals their immune system identifies them as a' threat' and produces an appropriate defence response. The most common causes of allergic reactions are: pollen from flowers, proteins secreted from house dust mites, moulds, foods such as peanuts, milk and eggs, pets such as cats and dogs, insects such as wasps and bees, and medicines. These substances cause swelling, inflammation and itching of the surrounding tissues, which is extremely irritating and uncomfortable. Common symptoms associated with allergic conditions include: sneezing, wheezing / coughing / shortness of breath, sinus pain / runny nose, nettle rash / hives, swelling, itchy eyes, ears, lips throat and mouth, sickness, vomiting & diarrhea. This book explains the types, effects, signs and symptoms of allergy on an individual.