Causes of Asthma
Although research has revealed much about asthma over recent decades, we still don't really understand what causes the disease. We have more and more pieces of intriguing information about asthma, but we don't know how those pieces will end up fitting together. Some pieces will be causes; some will be contributing factors; and some will be dead ends.
UI Health's asthma clinic is proud to participate in the ongoing research that will someday help us fully understand the factors that lead to this disease.
WHAT CAUSES ASHTMA?
Through ongoing research, we continue to draw closer to the day when all the pieces are in place. When we know what causes asthma, we will be much better equipped to prevent it and possibly to cure it.
Until then, we have some interesting puzzle pieces to work with.
Genetics
One risk factor for asthma is a condition called atopy, which is essentially a predisposition to be allergic to things. The evidence is quite clear that heredity is partially responsible for a person having atopy.
We know that genes contribute to atopy, which is a risk factor for asthma. But are there specific asthma genes? The answer is but the evidence is convincing that asthma is not a "single-gene" disease. Involvement of several different genes, though, in such asthma components as airway hyperresponsiveness and non-atopy-related inflammation seems likely but has not been proven.
Infections
A large percentage — probably about one-third — of babies and young children will experience wheezing at some point, usually during a viral respiratory infection. Some but not all of these children go on to have chronic asthma. It is unclear just what the role of the viral infection is, but it is possible that it is part of the cause of asthma.
The viruses that most commonly cause wheezing in infants are RSV (respiratory syncytial virus) and parainfluenza virus. In slightly older children, rhinovirus — the virus responsible for the common cold — is a frequent cause of wheezing.
Air Quality
The evidence is clear that air pollution can have a negative effect on the breathing of people who already have asthma.
Particulate matter (tiny particles of liquids and solids) in the air has also been shown to have adverse effects on breathing in general, particularly (but not exclusively) in people who already have respiratory problems.
It is unfortunately very difficult, though, to do research that can tell us whether or not air pollution actually causes asthma in people who don't already have the disease.
Cigarette Smoke
The case against cigarette smoke is even stronger than the case against air pollution.
It is thought that exposure to cigarette smoke in childhood contributes both directly and indirectly to the development of asthma.
In study after study, children exposed to tobacco smoke in the home have been shown to have higher rates of hospitalizations for respiratory illness. Serious respiratory illness before the age of 2 is an important risk factor for asthma.
It is believed that cigarette smoke also has a more direct role in causing asthma, either through effects on the immune system, on the formation of the airways, or both. Exposure to cigarette smoke in utero (through the mother smoking during pregnancy) appears to be at least as harmful as exposure in the home during infancy and early childhood. The risks also rise as the amount of cigarette smoke exposure rises due to an effect called "dose response" ( usually seen as evidence of a causal link).
First World/Third World Difference
Another observation that may hold clues to the causes of asthma is that asthma is much more common in industrialized nations — such as the United States — than in the developing world. We still do not know why this is so. It is unlikely to be related to the genetic makeup of the populations, since descendants of immigrants from developing nations to industrialized ones have similar asthma rates to those in their adoptive country.
Several explanations have been suggested to explain the higher prevalence of asthma in industrialized nations:
- Higher rates of different infectious diseases in the developing world — from measles to malaria, bacteria to parasitic worms — may somehow affect people's immune systems in a way that is protective against asthma.
- Spending more time indoors than their developing nation counterparts may expose children in industrialized nations to allergens or pollutants that contribute to asthma.
- Excess body weight may be a risk factor for asthma. And children in developing nations are thinner than children in industrialized nations.
How Might Causes of Asthma Fit Together?
One theory for explaining how asthma is caused involves a combination of underlying susceptibility with environmental exposures, often referred to as "hits." Under such a model, it is believed that a person who is not born with a genetic susceptibility to asthma will never get the disease, no matter what the environment. A person who is born genetically vulnerable to asthma also may escape the disease if he or she is not exposed to enough "hits" in the environment to bring it out. Asthma occurs, by this theory, only when a person both is susceptible (through heredity) and experiences those factors (still unidentified) that cause the disease to manifest itself.
This is all rather complex, but the picture may in fact be more complicated still. Some scientists believe that what we call "asthma" is actually several different diseases, caused in different ways. It is possible, for instance, that asthma that begins in infancy or childhood could be something else entirely from asthma that comes on in adulthood. Or perhaps asthma in people with allergies could be a different entity from asthma in people who are not allergic. These are some of the questions that asthma researchers are currently attempting to address.
No Matter What Causes Asthma, Treatment Can Help
If you have asthma, it's important to take steps to manage the disease. The asthma doctors at UI Health can help you understand what triggers your asthma and recommend medications and lifestyle changes that can help you keep the disease in check.
To make an appointment with one of our asthma doctors, please fill out the online form or call 312.996.3300.
