An allergy is typically a damaging immune system response to something foreign, such as food, dust, pollen, etc. Most people who have allergies tend to be sensitive to more than one thing. While allergies show obvious signs, it can be difficult to self diagnose the cause. If you think you have an allergy, refer to our different detailed topics on allergies that range from allergy types, allergy symptoms, allergy causes, allergy prevention, diagnosing allergy and much more. Remember, your only shield against an allergy attack is knowing all about it.