Causes of Asthma

To understand asthma, it helps to know how the airways work. The airways are tubes that carry air into and out of your lungs. People who have asthma have inflamed airways. The inflammation makes the airways swollen and very sensitive. The airways tend to react strongly to certain inhaled substances.

When the airways react, the muscles around them tighten. This narrows the airways, causing less air to flow into the lungs. The swelling also can worsen, making the airways even narrower. Cells in the airways might make more mucus than usual. Mucus is a sticky, thick liquid that can further narrow the airways.

This chain reaction can result in asthma symptoms. Symptoms can happen each time the airways are inflamed.

Source: NHLBI (NIH)1

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Back to: « Asthma

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What Causes Asthma?

The exact cause of asthma isn't known. Researchers think some genetic and environmental factors interact to cause asthma, most often early in life. These factors include:

If asthma or atopy runs in your family, exposure to irritants (for example, tobacco smoke) may make your airways more reactive to substances in the air.

Some factors may be more likely to cause asthma in some people than in others. Researchers continue to explore what causes asthma.

The "Hygiene Hypothesis"

One theory researchers have for what causes asthma is the "hygiene hypothesis." They believe that our Western lifestyle—with its emphasis on hygiene and sanitation—has resulted in changes in our living conditions and an overall decline in infections in early childhood.

Many young children no longer have the same types of environmental exposures and infections as children did in the past. This affects the way that young children's immune systems develop during very early childhood, and it may increase their risk for atopy and asthma. This is especially true for children who have close family members with one or both of these conditions.

Source: NHLBI (NIH)2

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The underlying causes of asthma are still unclear. Researchers believe asthma is caused by a combination of your genes and environmental factors. If you have allergies or a parent who has asthma, you’re at increased risk for the disease. Obesity and exposure to cigarette smoke may also raise the risk of developing asthma. NIH scientists are continuing to investigate the causes of this disease.

Source: NIH News in Health (NIH)3

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Asthma affects more than 6 million children nationwide. Previous studies have linked childhood asthma to indoor mold, which can thrive in homes with moisture problems. The connection between mold and asthma, however, is complicated and not fully understood. Asthma is often associated with allergies, and molds release tiny particles into the air that can cause allergic reactions.

Three particular species of mold were most associated with asthma. These species—Aspergillus ochraceus, Aspergillus unguis and Penicillium variabile—are common to water-damaged buildings.

The link between the 3 molds and asthma doesn’t prove that the molds cause asthma on their own. But it does provide evidence that indoor mold can contribute to the development of asthma.

Source: NIH News in Health (NIH)4

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Asthma is a disease that’s caused by swelling and inflammation of your airways. When your airways become narrower, less air can get through to your lungs. That’s what causes the wheezing (a whistling sound when you breathe), coughing, chest tightness and trouble breathing that we know as the symptoms of asthma.

Source: NIH News in Health (NIH)5

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In many people, asthma appears to be an allergic reaction to substances commonly breathed in through the air, such as animal dander, pollen, or dust mite and cockroach waste products. The catch-all name for these substances, allergens, refers to anything that provokes an allergic reaction. Some people have a genetic predisposition to react to certain allergens.

When these people breathe in the allergen, the immune system goes into high gear as if fighting off a harmful parasite. The system produces a molecule called immunoglobulin E (IgE), one of a class of defensive molecules termed antibodies. The IgE antibody is central to the allergic reaction. For example, it causes mast cells, a type of specialized defensive cell, to release chemical " weapons " into the airways. The airways then become inflamed and constricted, leading to coughing, wheezing, and difficulty breathing -- an asthma attack (definition provided by the US National Institute of Allergy and Infectious Diseases).

Source: EC (EU)6

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In approximately 15% of asthmatics, the illness may have been caused, or made worse, by workplace exposures. Some occupational exposures are well known risks for asthma development (e.g., western red cedar; isocyanates). Indoor environment research has identified evidence of an association between damp buildings and asthma symptoms in individuals with pre-existing asthma.

There is also new evidence of an association between damp buildings and new-onset asthma. In an individual with new-onset asthma or worsening of stable pre-existing asthma, measurements of lung function made several times a day at work and at home over several weeks may reveal a pattern of changing lung function that suggests a workplace cause.

Source: CDC NIOSH7

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Asthma, … results from an over-reaction of the immune system.

Source: NCBI, Genes and Disease (NCBI/NIH)8

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If you have asthma, the inside walls of your airways become sore and swollen. That makes them very sensitive, and they may react strongly to things that you are allergic to or find irritating. When your airways react, they get narrower and your lungs get less air.

Source: MedLinePlus (NIH)9

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Airways are tubes that carry air into and out of your lungs. People with asthma have inflamed airways. They are swollen, very sensitive, and tend to react strongly to some inhaled substances.

When airways react, surrounding muscles tighten, airways narrow, and less air flows into the lungs. Swelling can worsen, making airways even narrower. There may be more mucus than normal, causing further narrowing.

This chain reaction can cause asthma symptoms. Sometimes, symptoms are mild and go away on their own or after treatment with medicine. Other times, they may get worse. If you have more symptoms or they get worse, you're having an asthma attack.

It's important to treat symptoms when they first appear to prevent them from getting worse and causing severe attacks. Severe attacks require emergency care and can be fatal.

Source: MedLinePlus Magazine (NIH)10

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Asthma can be triggered by:

Some medicines, physical activities, smoke, chemicals and gases can also cause asthma.

Source: New Zealand Health11

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Causes and triggers

Asthma is caused by swelling (inflammation) of the breathing tubes that carry air in and out of the lungs. This makes the tubes highly sensitive, so they temporarily narrow.

It may occur randomly or after exposure to a trigger. Common asthma triggers include:

Identifying and avoiding your asthma triggers can help you keep your symptoms under control.

Read more about the causes of asthma.

Source: NHS Choices UK12

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The exact cause of asthma is unknown.

People with asthma have swollen (inflamed) and "sensitive" airways that become narrow and clogged with sticky mucus in response to certain triggers.

Genetics, pollution and modern hygiene standards have been suggested as causes, but there's not currently enough evidence to know if any of these do cause asthma.

Source: NHS Choices UK13

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Indoor Allergens: Studies in the last 10 years have shows that indoor allergens from house dust mites, cockroaches, dogs, cats, rodents, molds and fungi are among the most important asthma triggers.

“Home carpeting can be a problem because children can develop asthmatic reactions to the house dust mites that live in the carpet,” says Dr. David Schwartz, director of the NIH’s National Institute of Environmental Health Sciences (NIEHS).

Source: NIH News in Health (NIH)14

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Cladosporium: Cladosporium has also been associated with allergies and asthma.

Source: CDC15

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Allergies: Are allergies related to asthma?

Yes. Asthma can be triggered by substances in the environment called allergens. Some indoor allergens come from dust mites, cockroaches, dogs, cats, rodents, molds, and fungi. Outdoor allergens include pollen from many trees, weeds, and grass. Even food allergies can cause asthma symptoms.

Source: MedLinePlus Magazine (NIH)16

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Air Pollution: What about air pollution outside?

Outdoor pollution plays a major role, as does cigarette smoke. Children exposed to pollution are more likely to develop asthma. Asthma patients are more likely to have their asthma flare up when they are exposed to pollution. This is why asthma patients should not exercise outdoors during high-pollution days, for example when there is a code-orange ozone day.

Source: MedLinePlus Magazine (NIH)17

Causes of Asthma

Causes of the condition may include:18 Causes of Asthma:

Triggers for Asthma

What Causes Asthma Symptoms To Occur?

Many things can trigger or worsen asthma symptoms. Your doctor will help you find out which things (sometimes called triggers) may cause your asthma to flare up if you come in contact with them. Triggers may include:

  • Allergens from dust, animal fur, cockroaches, mold, and pollens from trees, grasses, and flowers
  • Irritants such as cigarette smoke, air pollution, chemicals or dust in the workplace, compounds in home décor products, and sprays (such as hairspray)
  • Medicines such as aspirin or other nonsteroidal anti-inflammatory drugs and nonselective beta-blockers
  • Sulfites in foods and drinks
  • Viral upper respiratory infections, such as colds
  • Physical activity, including exercise

Other health conditions can make asthma harder to manage. Examples of these conditions include a runny nose, sinus infections, reflux disease, psychological stress, and sleep apnea. These conditions need treatment as part of an overall asthma care plan.

Asthma is different for each person. Some of the triggers listed above may not affect you. Other triggers that do affect you may not be on the list. Talk with your doctor about the things that seem to make your asthma worse.

Source: NHLBI (NIH)19

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The airways of people with asthma are prone to inflammation, which causes the airways to swell and narrow. They become extra sensitive to certain substances that are breathed in. These are called “triggers.”

Asthma triggers can worsen inflammation and cause the muscles around the airways to tighten, further shrinking air passages and making it harder to breathe. Cells in the airways might also produce excess mucus (a sticky, thick liquid), making the airways even narrower.

Common asthma triggers include cigarette smoke, air pollution, mold, house dust mites, and furry animal dander. Other asthma triggers include weather changes, exercise, stress, and respiratory infections like common colds.

“Preventing such infections is important,” stresses Dr. Stewart Levine, an asthma expert at NIH. “People who have asthma should also obtain a flu shot, as they may be at higher risk for flu-related complications.”

Source: NIH News in Health (NIH)20

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A variety of "triggers" may initiate or worsen an asthma attack, including viral respiratory infections, exercise, and exposure to irritants such as tobacco smoke.

Source: NCBI, Genes and Disease (NCBI/NIH)21

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How do you suggest approaching potential triggers with children?

In terms of medication, you should use as much as necessary and as little as possible. When you can influence asthma symptoms by changing something in the environment that’s always the preferred way. Some scientists think that keeping our children’s environment too clean may prevent their immune system from learning to discriminate what is harmful and what is an innocent exposure. That may be a reason why allergies have become more common. I encourage my own children to play outdoors and that’s especially important when they’re young.

Source: MedLinePlus Magazine (NIH)22

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Asthma attacks can be triggered by viral infections, cold air, exercise, anxiety, allergens, and other factors.

Source: MedLinePlus Magazine (NIH)23

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Allergens, pollutants, and irritants can bring on symptoms. So can exercise, but do not avoid it. Physical activity is important for health. Discuss with your health professional asthma medicines that can help you stay active.

Source: MedLinePlus Magazine (NIH)24

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Asthma triggers

Asthma symptoms often occur in response to a trigger. Common triggers include:

Once you know your triggers, trying to avoid them may help control your asthma symptoms.

Asthma UK has more information on asthma triggers.

Source: NHS Choices UK25

Causes List for Asthma

Some of the possible causes of Asthma or similar disorders may include:26

... Full Causes List for Asthma »

Genetics of Asthma

Research shows that asthma runs in families. When one or both parents have asthma, a child is more likely to develop it, too. This is known as genetic susceptibility. ...Source: NIH News in Health (NIH)27 ...

... More on Genetics »

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  1. Source: NHLBI (NIH): health/ health-topics/ topics/ asthma
  2. Source: NHLBI (NIH): health/ health-topics/ topics/ asthma/ causes
  3. Source: NIH News in Health (NIH): issue/ jun2014/ feature1
  4. Source: NIH News in Health (NIH): issue/ sep2012/ capsule1
  5. Source: NIH News in Health (NIH): 2006/ July/ docs/ 01features_01.htm
  6. Source: EC (EU): health/ major_chronic_diseases/ diseases/ asthma_en
  7. Source: CDC NIOSH: niosh/ topics/ indoorenv/ moldsymptoms.html
  8. Source: NCBI, Genes and Disease (NCBI/NIH): books/ NBK22243/ 
  9. Source: MedLinePlus (NIH): asthma.html
  10. Source: MedLinePlus Magazine (NIH): magazine/ issues/ fall13/ articles/ fall13pg12-13.html
  11. Source: New Zealand Health: your-health/ conditions-and-treatments/ diseases-and-illnesses/ asthma
  12. Source: NHS Choices UK: conditions/ Asthma/ 
  13. Source: NHS Choices UK: conditions/ asthma/ causes/ 
  14. Source: NIH News in Health (NIH): 2006/ July/ docs/ 01features_01.htm
  15. Source: CDC: fungal/ diseases/ other/ index.html
  16. Source: MedLinePlus Magazine (NIH): magazine/ issues/ fall17/ articles/ fall17pg26.html
  17. ibid.
  18. Source: Human Phenotype Ontology
  19. Source: NHLBI (NIH): health/ health-topics/ topics/ asthma/ signs
  20. Source: NIH News in Health (NIH): issue/ jun2014/ feature1
  21. Source: NCBI, Genes and Disease (NCBI/NIH): books/ NBK22181/ 
  22. Source: MedLinePlus Magazine (NIH): magazine/ issues/ fall17/ articles/ fall17pg24.html
  23. Source: MedLinePlus Magazine (NIH): magazine/ issues/ spring15/ articles/ spring15pg26-27.html
  24. Source: MedLinePlus Magazine (NIH): magazine/ issues/ fall13/ articles/ fall13pg12-13.html
  25. Source: NHS Choices UK: conditions/ asthma/ causes/ 
  26. Source: Algorithmically Generated List
  27. Source: NIH News in Health (NIH): 2006/ July/ docs/ 01features_01.htm

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Note: This site is for informational purposes only and is not medical advice. See your doctor or other qualified medical professional for all your medical needs.