There is an ongoing debate as to whether or not allergies cause asthma. Many asthmatic children have allergies, so any theory that one might cause the other makes sense. So, the question is: Do allergies cause asthma?
Here are arguments for why that may be the case:
Childhood-onset asthma is often allergic. Childhood onset asthma is often associated with allergies. One cannot help but surmise that uncontrolled allergies can lead to asthma, especially considering that both diseases are associated with inflammation of the respiratory tract. Irritants of the upper airway tend to move down, if not by force of gravity, then by the nasobronchial reflex.
Eczema leads to asthma. Eczema is an allergic condition that causes dry and itchy skin. Research suggests that many children with eczema go on to develop asthma. In fact, many people with eczema have what doctors often refer to as "The Atopic March": eczema, allergies and asthma. (I wrote about the eczema/ asthma connection here.)
Nasal congestion causes asthma. Rhinitis is inflammation of the nasal passages due to an allergic response to such things as dust, pollen, molds and fungus. If chronic, it can result in sinusitis, from which a high percentage of asthmatic children suffer. Some scientists believe a nasobronchial reflex transfers inflammation of the upper respiratory tract (the nose and throat) to the lower respiratory tract (the air passages). In this way, irritants that stimulate the upper airway may result in inflammation of the lower airway. Some studies have shown that aggressive treatment of rhinitis can prevent asthma. (I wrote about this in more detail here.)
Allergies may precede asthma. Several studies have concluded that people with seasonal allergies are much more likely to develop asthma. However, other studies have found just the opposite. So, more research is needed.
Yet some studies have concluded that while only a small percentage of children with allergies have asthma, children with allergies have an increased risk of developing adult onset asthma, according to the New York Times.
Genetics is a factor. It's now generally accepted that there's a link between genetics and asthma. In many cases, the same genes or genetic changes that cause asthma also lead to allergies and eczema. Further research into this area of genetics should give us a more definitive answer to our question: Do allergies cause asthma? (I wrote about the asthma/ genetic link here.)
Surely, I could be wrong, but it does seem that in many people the allergic response occurred first, and that repeated exposure to allergens results in chronic inflammation of the respiratory tract. When inflammation in the lungs becomes chronic, this is referred to as asthma.
Increased inflammation of your air passages then makes you more sensitive to your asthma triggers. The best way to treat this airway inflammation, and prevent further asthma symptoms, is with medicines like inhaled corticosteroids.