Allergy symptoms occur when the body mistakenly reacts to these substances as if they were germs or viruses. In other words, in people who are allergic, the immune system works overtime. These substances may invade the body by being inhaled, swallowed or by direct contact with the skin. These sensitizing substances are called allergens.

Examples of these allergens are house dust mites, mold spores, tree pollens, ragweed, grass and animals like cats, dogs and horses and foods like peanuts and shellfish. In people who are allergic, these allergens can produce hay fever, asthma, sinus problems, ear pressure, itchy and red eyes, eczema or hives.
Non allergic factors may trigger allergy symptoms in some people. These factors are emotional stress, fatigue, infection, air pollution and weather changes. While most allergies are not life threatening, few people have anaphylaxis, especially with foods, which is an extreme allergic reaction and they should talk to their doctor about getting an emergency kit and wearing an ID bracelet.
Allergies tend to run in families. If your parents are allergic, it is more likely that you will also have allergies. However, you may not be allergic to the same substances.
Allergies may change from one type to another as people grow older. A baby who is allergic to a certain food might grow out of that allergy, develop asthma as an older child, then get hay fever as an adult.
Tobacco smoke is an irritant, not an allergen. However, for most people smoking or exposure to smoke can worsen allergic symptoms.
If you have allergies, it is important not to smoke and to avoid second hand smoke.

Some people will ask, "Will contact with an allergen always trigger a reaction?"
The answer to whether or not you have an allergic reaction depends partially on:
- • Your degree of sensitivity - this depends on the level of IGE (allergy antibodies) present in your blood and tissue.
- • The amount of the allergen to which you have been exposed.
- • The part of your body that was exposed, such as skin, nose, lungs, eyes or digestive tract.
