Antibody Response

• Allergies result from an exaggerated response of the body's immune system, which under normal conditions is designed to protect the body from a foreign and potentially dangerous invader. In a person with allergies, the immune response considers the substance as dangerous even though it may not be. In fact, exposure to an allergen can built up the immune response so that it becomes even stronger with repeated exposures to the substance.
  
  

Heredity

• Genetics play a big part in the development of allergies. The white cells that protect against bacteria and viruses can be more prone to allergies depending on heredity. A person whose family has a background of allergies may be susceptible to normally safe substances and the body defends itself by producing histamines. The risk of developing allergies increases 20 percent if a parent has allergies and 40 percent if both parents have allergies.
  
  

Environmental Factors

• If a person has another condition that weakens its defenses, she can develop allergies. In particular, asthma raises the risk. A child who is exposed to certain substances early in life may develop allergies though some of the reasons why one child develops allergies and another doesn't are still not completely understood.
  
  

Common Triggers

• Substances that are most often implicated in allergic reactions include a range of foods including peanuts, tree nuts, eggs, wheat, shellfish or milk. Other substances include bee stings, dust mites, mold or dog or cat fur, antibiotics and other substances such as latex. Responses to the allergens may be minor or life-threatening when the body goes into anaphylaxic shock.