Why Do Allergies Trigger Asthma? What Can You Do?

by John Bottrell Health Professional

Many of us have a double whammy that is often referred to as allergic asthma or extrinsic asthma. So what are allergies, and why do they make asthma worse?

The first time a person with a predisposition to develop allergies is exposed to an allergen--say dust mites--his immune system develops "special white blood cells (T-cells)" that "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 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. Their role is to help mediate the inflammatory response of the immune system. IgE antibodies can remain attached to mast cells for many years.

Once your body is sensitized, it's ready to do battle the next time you're exposed to dust mites. When you inhale the dust mite, it will attach itself immediately to a dust mite IgE, and cause the mast cell to release the mediators of inflammation. Those mediators are histamine, leukotrienes, and cytokines chemicals that allow immune cells to talk to each other.

This response is good if the invader is a bad parasite, bacteria or virus. But an allergy is a defense against allergens, things that are harmless to 90 percent of people.

The most common mediator is histamine. It opens small blood vessels causing them to leak fluid, resulting in warming and swelling of the skin, itching and watery eyes. Histamine causes sneezing and increased mucus production in the nasal cavity and airways that lead to runny nose, post nasal drip, and cough.

Another mediator is leukotriene, which causes inflammation of the muscles lining your air passages. If you have asthma, your air passages are already somewhat inflamed. An allergic response makes this worse and causes narrowed air passages, leading to asthma attacks.

This is why it's especially important for most asthmatics to keep their asthma under control with inhaled corticosteroids. These medicines help minimize chronic airway inflammation, so when you are exposed to allergens, they don't stir up your asthma at least not as much.

Other options are antihistamines, such as Claritin, leukotriene antagonists, such as Singulair, and IgE inhibitors, such as Xolair. And, of course, there's the old standby therapy called "Allergen Avoidance."

One or a combination of these options work for many allergic asthmatics, but others continue to struggle. It seems that despite all the improvements in asthma and allergy medicines, allergens continue to be an annoyance.

John Bottrell
Meet Our Writer
John Bottrell

John Bottrell is a registered Respiratory Therapist. He wrote for HealthCentral as a health professional for Asthma and Chronic Obstructive Pulmonary Disease (COPD).