How did I become allergic?
Primary Exposure (Sensitization)
An allergen such as mold spores or pollen enters the body through the mouth or nose or lands on the skin. Special white blood cells (T-cells) recognize the allergen as foreign and release chemicals in response. These chemicals travel through the blood and instruct another kind of white blood cell (B-cells) to produce millions of IgE antibodies. Some of these antibodies attach to the outside of another special type of white blood cell called a mast cell. Mast cells are scattered throughout the skin and respiratory tract and their purpose is to help mediate the inflammatory response of the immune system. IgE antibodies can remain attached to mast cells for many years.
Re-Exposure: The Cause of Allergy Symptoms
When the same allergen is encountered again, it binds directly to the IgE antibody stuck to the outside of mast cells. This causes the mast cells to release chemicals such as histamine. Histamine is an example of a chemical mediator – special ‘messenger’ chemicals that immune cells use to talk to each other.
Histamine is one of the most well-known mediators - it is responsible for causing allergy and asthma symptoms. Histamine opens small blood vessels causing them to leak fluid. This results in inflammation: warming and swelling of the skin, itching, and watery eyes. Histamine causes sneezing and increased mucus production in the nasal cavity and airways that leads to runny nose, post-nasal drip, and cough. Histamine can also cause tightening of smooth muscle in the airways that results in asthma symptoms like wheezing and shortness of breath.
The timing of allergy symptoms may be immediate or delayed.
Delayed allergic response may be the cause of nighttime allergic asthma attacks.
Read a hypothetical story about how allergy happens.
See how an invisible cloud of ragweed pollen descends upon a town and sensitizes a little girl.
Why am I allergic to only certain things?
Some people are allergic to lots of things, others to very few things. The environment, genetics, and the immune system all play a role.
This information has been approved by David Tinkelman, MD (February 2006).
