Allergies and asthma: They often occur together

How does an allergic reaction cause asthma symptoms?

An allergic response affects the lining of the nose and the lining of the airways in a similar way. Symptoms occur when antibodies in your blood are exposed to an allergy-causing substance (allergen). These antibodies can trigger allergy symptoms such as nasal congestion, scratchy eyes or a skin reaction — and for many, inflammation of the airways associated with asthma.
For example, if your immune system produces allergy antibodies when you're exposed to cats, you're said to have a cat allergy. Proteins in cat fur or cat dander trigger the release of chemicals that cause inflammation and swelling in the lining of the nose. If you have allergic asthma, your reaction to cat fur or dander can also cause the lower airways to become inflamed, triggering asthma symptoms.

If I treat my allergies, will it prevent asthma?

Some allergy treatments can reduce asthma symptoms. A type of allergy treatment called allergy shots (immunotherapy) can help treat asthma by gradually reducing your immune system response to allergens that cause your asthma symptoms.
If you have allergic asthma, avoiding the allergic substances that trigger your symptoms can reduce asthma and in some cases, control it completely.

Are allergies and asthma treated differently?

Some medications work for both allergies and asthma, but may be taken differently. For example, corticosteroids which you spray into your nose reduce inflammation from hay fever. Corticosteroid creams applied to your skin reduce inflammation by an allergic skin reaction. And inhaled corticosteroids, which you breathe into your lungs using an inhaler device, reduce inflammation of the bronchial tubes caused by asthma.
Taken in pill form, montelukast (Singulair) is used to help with symptoms caused by both allergies and asthma. Called a leukotriene modifier, this medication helps regulate the immune system chemicals released during an allergic reaction.
Certain other medications are clearly more effective for one condition over another. Antihistamines, for example, are commonly used to treat hay fever but don't work well in treating asthma. Bronchodilator inhalers, which open congested airways, are a big part of asthma treatment, though they aren't used to treat hay fever.