In most cases involving allergies, the body's immune system overreacts to allergens (foreign objects in the body), and produces excessive reactive symptoms.   When a foreign object enters the body of an allergic person, the immune system produces IgE antibodies for that specific allergen. The next time that the allergen enters the body, IgE antibodies attempt to find the allergen ... and can trigger the release of several chemicals, including histamine.  The chemicals create symptoms of allergies including inflammation, coughing, sneezing, asthma, and other allergic reactions.  

Common allergens include:

• Cockroach droppings
• Dust 
• Mites 
• Food 
• Insect stings 
• Latex
• Medicines 
• Mold spores 
• Pet dander 
• Pollen

Risk factors
The environment may play a role determining which allergens people react to. Family medical history also plays a role in predicting allergic reaction. For example, if a parent has been diagnosed with allergies, then children are more likely to experience the same allergies, especially if both parents have allergic reactions.  And, if you have allergies for one type of allergen, then you are more likely to have allergic reactions to other types of allergens.   However, while family history is important to understanding if you may have allergies similar to your family, it is important to remember that not everyone develops allergies even when exposed to the same allergen.  

Allergic reactions differ according to the type of allergen (e.g. plants versus chemicals), and physical location affected (e.g. skin or a runny nose).  In most cases, allergic reactions are not dangerous, although they can be uncomfortable.  Severe allergic reactions to an insect sting or medication that can result in life-threatening conditions are known as anaphylaxis; this condition requires immediate emergency medical attention to prevent death. To better understand common symptoms of allergies and compare these with more serious allergic reactions, read our Symptoms of allergic reaction section now for more information.