An allergy is an overreaction of the immune system to a substance which in the majority of people causes no symptoms. These substances, also known as allergens, can cause allergic reactions. Examples of allergens include pollen, dust, mold, pets, foods and drugs. The body's immune system overreacts by attacking the allergens and releasing chemicals in attempts to protect itself. Chemicals that are released interact with other cells in the body cause allergic symptoms such as sneezing, stuffy nose, itchy eyes and cough.

How do allergies develop?

Allergies have a strong genetic component. If you have allergies, it is very likely that one or both your parents have allergies, too. Sometimes allergy symptoms that start in childhood can disappear for many years and then recur as an adult. In addition, children who have allergies do not always develop the same allergies as their parents.

What are common symptoms of allergies?

These are the most common symptoms associated with allergies:
• Sneeze
• Runny nose
• Nasal congestion
• Postnasal drip
• Cough
• Wheeze
• Itchy, tearing eyes
• Rashes
These are less common symptoms associated with allergies:
• Headache
• Loss of smell or taste
• Fatigue
• Snoring

What are the different types of allergic diseases?

An allergic reaction can affect any part of the body but symptoms are most often felt in the nose, eyes, sinuses, lungs, lining of the stomach, throat and skin. These are places where immune cells are located and ready to fight invaders that come in contact with the skin or are inhaled or swallowed.

• Allergic rhinitis (hay fever) is a disorder that describes allergic reactions in the nose and sinus passages. Symptoms include sneezing, stuffy nose, runny nose and itching of the nose. When these symptoms are triggered by pollen or mold during the spring, summer or fall seasons, it is often described as "hay fever" or seasonal allergy.
• Eye allergies are often caused by outdoor allergens (pollen or mold) or indoor allergens (dust, pets) and symptoms include itchy and watery eyes.
• Asthma is a disease that affects the airways in the lungs making them inflamed and swollen. Airway inflammation can be caused by allergens, smoke, cold air, infection, exercise or stress. Muscles lining airways spasm and block the flow of air to the lungs causing symptoms of shortness of breath, difficulty breathing, coughing or wheezing.
• Skin allergies (contact dermatitis, eczema and hives) are skin reactions that can be caused by allergens and irritants. Reactions may be immediate or delayed as in poison ivy. Common allergens can be foods, animals, drugs or insect stings.
• Food allergies can cause a variety of symptoms including nausea, vomiting, indigestion, diarrhea, skin rashes, headaches, wheeze and nasal congestion. Food allergy can also cause a life-threatening reaction called anaphylaxis. Milk, eggs, soy, wheat, shellfish, peanuts and tree nuts are the most common food allergies in children. Peanuts, tree nuts and shellfish are the most common food allergies in adults.
• Sinus infections are common with people with allergies because persistent nasal congestion causes inflammation of the nasal and sinus passages. Symptoms may include thick nasal discharge, cough, and sometimes jaw or teeth pain.

How do you test for allergies?

Allergy skin testing is a safe and effective way to find out exactly what you allergic to. Allergy skin testing is performed in both children and adults and is the most accurate and preferred method of evaluating allergies. These tests are safe, minimally invasive, and easily interpreted. Allergy skin testing is a simple procedure that introduces a very small amount of specific allergens introduced through an indention or "prick" on the surface of the skin. The results are available within minutes.