Asthma is a chronic disease of the airways that transport air to and from the lungs. No full cure is available, but management methods can help a person with asthma lead a full and active life.

In a person with asthma, the inside walls of the airways, known as bronchial tubes, become swollen or inflamed. This swelling or inflammation makes the airways extremely sensitive to irritations and increases their susceptibility to an allergic reaction.

In an allergic reaction, the airways swell, and the muscles around the airway tighten, making it difficult for air to move in and out of the lungs.

In the United States, around 8.3 percent of people have a form of asthma. There are many types of asthma, as well as a range of factors that can cause the disease.

In this article, we provide an overview of this complex respiratory condition, as well as exploring the different types and causes and how a doctor might diagnose the condition.

What is asthma?

Asthma is an incurable illness of the airways. The disease causes inflammation and narrowing inside the lung, restricting air supply.

The symptoms of asthma often present in periodic attacks or episodes of tightness in the chest, wheezing, breathlessness, and coughing.

During the development of asthma, the airways swell and become extremely sensitive to some of the substances a person might inhale.

When this increased sensitivity causes a reaction, the muscles that control the airways tighten. In doing so, they might restrict the airways even further and trigger an overproduction of mucus.

Asthma attacks

The set of inflammatory events in the respiratory system can lead to the severe symptoms of an asthma attack.

Worldwide, around 250,000 people die every year as a result of asthma.

Asthma attacks occur when symptoms are at their peak. They might begin suddenly and can range from mild to severe.

In some asthma attacks, swelling in the airways can completely prevent oxygen from reaching the lungs, which also stops it entering the bloodstream and traveling to vital organs.

This type of asthma attack can be fatal and requires urgent hospitalization.

At the start of an asthma attack, the airways allow enough air into the lungs, but it does not let the carbon dioxide leave the lungs at a fast enough rate. Carbon dioxide is poisonous if the body does not expel the gas, and a prolonged asthma attack might lead to a build-up of the gas in the lungs.

This might further reduce the amount of oxygen entering the bloodstream.

People with clear symptoms of asthma should visit a doctor. They will provide treatments and advise on management techniques, as well as identifying potential triggers for asthma symptoms and how to avoid them. The doctor will also prescribe medications to help reduce the frequency of attacks asthma.

Effective asthma control reduces the impact of the condition on everyday living.


As many different factors come together to cause asthma, there are many different types of the disease, separated by age and severity.

Adults and children share the same triggers for symptoms that set off an allergic response in the airways, including airborne pollutants, mold, mildew, and cigarette smoke.

Childhood asthma

Children are more likely to have an intermittent form of asthma that presents in severe attacks. Some children might experience daily symptoms, but the common characteristic among children with asthma is a heightened sensitivity to substances that cause allergy.

Second-hand tobacco smoke causes severe problems for children with asthma. Between 400,000 and 1 million children experience worsening asthma symptoms as a result of second-hand smoke, according to the American Lung Association.

The Centers for Disease Control and Prevention (CDC) advise that children experience more emergency visits and admissions for asthma than adults.

Mild asthma might resolve without treatment during childhood. However, there is still a risk that the condition might return later on, especially if symptoms are moderate or severe.

Adult-onset asthma

Asthma in adults is often persistent and requires the daily management of flare-ups and preventing symptoms. Asthma can begin at any age.

Allergies lead to at least 30 percent of adult presentations of asthma. Obesity is a strong risk factor for adult-onset asthma, and women are more likely to develop the condition after the age of 20 years.

People over 65 years of age make up a large number of deaths from asthma.

Occupational asthma

This is a type of asthma that occurs as a direct result of a job or profession.

Symptoms will become apparent after attending a particular workplace. Industries with regular associations to occupational asthma include baking, laboratory work, or manufacturing.

In this type, the work environment leads to the return of childhood asthma or the start of adult-onset asthma.

Other symptoms might include a runny nose and red eyes.

Difficult-to-control and severe asthma

These types involve consistent, debilitating asthma symptoms and breathing difficulties. Around 12 percent of people with asthma have difficult-to-control or severe asthma.

With the correct medication and effective trigger avoidance, those in this category can bring asthma symptoms back under control.

Roughly 5 percent of people with asthma do not see improvements after using the standard asthma medications. These people have severe asthma, and there are several types of severe asthma depending on the cause.

Newer medications are becoming available to address the different forms of severe asthma, such as eosinophilic asthma that does not link to any allergic reactions.

Seasonal asthma

This type occurs in response to allergens that are only in the surrounding environment at certain times of year, such as cold air in the winter or pollen during hay fever season.

People still have asthma for the rest of the year but do not experience symptoms.


Many different aspects of a person’s environment and genetic makeup can contribute to the development of asthma.

Asthma is the most common chronic disease among children. The first symptoms become clear at around 5 years of age in the form of wheezing and regular infections in the respiratory tracts.

The following are the primary causes of asthma.


A strong link exists between allergies and asthma.

One 2013 study in the Annals of Asthma, Allergy, and Immunology suggests that over 65 percent of adults with asthma over the age of 55 years also have an allergy, and the figure is closer to 75 percent for adults between the ages of 20 and 40 years.

Common sources of indoor allergens include animal proteins, mostly from cat and dog dander, dust mites, cockroaches, and fungi.

Smoking tobacco

Research has linked tobacco smoke to an increased risk of asthma, wheezing, respiratory infections, and death from asthma. In addition, the children of parents who smoke have a higher risk of developing asthma.

Smoking makes the effects of asthma on the airways worse by adding coughing and breathlessness to its symptoms, as well as increasing the risk of infections from the overproduction of mucus.

Environmental factors

Air pollution both in and out of the home can impact the development and triggers of asthma.

Allergic reactions and asthma symptoms often occur because of indoor air pollution from mold or noxious fumes from household cleaners and paints.

Other asthma triggers in the home and environment include:

  • pollution
  • sulphur dioxide
  • nitrogen oxide
  • ozone
  • cold temperatures
  • high humidity

Heavy air pollution tends to cause a higher recurrence of asthma symptoms and hospital admissions.

Smoggy conditions release the destructive ingredient known as ozone, causing coughing, shortness of breath, and even chest pain. These same conditions emit sulfur dioxide, which also results in asthma attacks by constricting the airways.

Changes in the weather might also stimulate attacks. Cold air can lead to airway congestion, constricted airway, extra secretions of mucus, and a reduced ability to clear that mucus.

Humidity might also lead to breathing difficulties for populations in some areas.


Some studies, such as this report from 2014, suggest a link between obesity and asthma, although the American Academy of Asthma, Allergies, and Immunology does not recognize obesity as a formal risk factor for asthma.

However, the report in question suggests that the inflammatory mechanisms that drive asthma also link to obesity.


If a woman smokes tobacco or illicit substanes while pregnant, an unborn child might grow less in the womb, experience complications during labor and delivery, and have a low birth weight.

These newborns might be more prone to medical problems, including asthma.


People who undergo stress have higher asthma rates. Increases in asthma-related behaviors during stressful times, such as smoking, might explain these increased rates.

Emotional responses, including laughter and grief, might trigger asthma attacks.


A parent can pass asthma on to their child. If one parent has asthma, there is a 25 percent chance that a child will develop asthma. Having two parents with asthma increase the risk to 50 percent.

Many genes are involved in passing on asthma. These genes can interact with the environment to become active, although confirming these findings may require further research.


Atopy is a general class of allergic hypersensitivity that leads to allergic reactions in different parts of the body that do not come in contact with an allergen. Examples include eczema, hay fever, and an eye condition called allergic conjunctivitis.

During atopy, the body produces more immunoglobin (IgE) antibodies than usual in response to common allergens.

The most common type of asthma is atopic asthma, and atopy plays a key role in its development. Environmental allergens lead to overproduction of IgE antibodies and trigger asthmatic reactions.

The menstrual cycle

One type of asthma, known as perimenstrual asthma (PMA), leads to acute symptoms during the menstrual cycle and a particular sensitivity to aspirin.

The sex hormones that circulate during menstruation, such as luteinizing hormone (LH) and follicle-stimulating hormone (FSH), impact immune activity. This increased immune action can cause hypersensitivity in the airways.


Three main components comprise an accurate asthma diagnosis: Medical history, observations during a physical exam, and results from breathing tests.

A primary care physician will administer these tests and determine the level of asthma as mild, intermittent, moderate, or severe in people who show signs of the condition, as well as identifying the type.

A detailed family history of asthma and allergies can help a doctor make an accurate diagnosis. A personal history of allergies is also important to mention, as many share mechanisms with asthma and increase the risk.

Keep a note of any potential triggers of asthma symptoms to help guide treatment, including information about any potential irritants in the workplace.

Be sure to identify any health conditions that can interfere with asthma management, such as:

  • a runny nose
  • sinus infections
  • acid reflux
  • psychological stress
  • sleep apnea

Young children who develop asthma symptoms before the age of 5 years find it more difficult to receive a clear diagnosis. Doctors might confuse asthma symptoms with those of other childhood conditions.

If children experience wheezing episodes during colds or respiratory infections in early life, they are likely to develop asthma after 6 years of age.

Physical exam

A physical examination will generally focus on the upper respiratory tract, chest, and skin. A doctor will listen for signs of wheezing, or a high-pitched whistle on breathing out, in the lungs during a breath using a stethoscope. Wheezing is a key sign of both an obstructed airway and asthma.

Physicians will also check for a runny nose, swollen nasal passages, and soft growths on the inside of the nose and check for skin conditions including eczema and hives. These are allergic conditions that link to asthma and suggest heightened immune activity that could be causing any wheezing.

People with asthma do not always show physical symptoms, and it is possible to have asthma without presenting any physical maladies during an examination.

Asthma tests

Lung function tests are another component of an asthma diagnosis. They measure how much air a person inhales and exhales and the speed with which a person can expel air from the lungs.

A spirometry test can provide an indication of lung function.

Spirometry is a non-invasive test that requires deep breaths and forceful exhalation into a hose. The hose links to a machine called a spirometer that displays two key measurements:

  • forced vital capacity (FVC), or the maximum amount of air a person can inhale and exhale
  • forced expiratory volume (FEV-1), the maximum amount of air a person can exhale in one second

The doctor then compares these measurements against what would be normal for another person of the same age. Measurements below normal indicate obstructed airways and probable asthma.

A doctor will often administer a bronchodilator drug to open air passages before retesting with the spirometer to confirm the diagnosis. If results improve after using the drug, the risk of an asthma diagnosis increases.

Children under 5 years of age are difficult to test using spirometry, so asthma diagnoses will rely mostly on symptoms, medical histories, and other parts of the physical examination process.

In younger children, doctors commonly prescribe asthma medicines for 4 to 6 weeks to gauge physical response.

Other Tests

A bronchoprovocation test, also known as a “challenge test” involves the administration an airway-constricting substance, such as cold air, to deliberately trigger airway obstruction and asthma symptoms.

Similarly, a challenge test for exercise-induced asthma would consist of vigorous exercise with the aim of triggering symptoms. The doctor then conducts a spirometry, and if measurements are still normal, they are not likely to reach a diagnosis of asthma.

Physicians might use allergy tests to identify substances that may be causing asthma or making it worse. These tests do not fully diagnose asthma, but they might help a doctor understand the nature of asthma symptoms.

Doctors may also test for other diseases with similar symptoms, such as:

  • gastroesophageal reflux disease (GERD)
  • heartburn
  • hay fever
  • sinusitis
  • sleep apnea
  • chronic obstructive pulmonary disease (COPD)
  • airway tumors
  • airway obstruction
  • bronchitis
  • pneumonia
  • a blood clot in the lung, or pulmonary embolism
  • congestive heart failure
  • vocal cord dysfunction
  • viral lower respiratory tract infection

A doctor may test for these using the following methods:

  • a chest x-ray
  • electrocardiogram (ECG)
  • complete blood counts
  • CT scans of the lungs
  • gastroesophageal reflux assessment
  • the induction and examination of sputum, or phlegm

Many people with asthma will not need to visit a specialist, as most primary care physicians have training for asthma diagnosis. People who require special asthma tests or have had life-threatening asthma attacks in the past may need to visit an asthma specialist

Specialists can also be useful for people who need more than one kind of medication or higher, more concentrated doses in order to control asthma. A visit may also be necessary for people with difficult-to-control asthma, or people receiving treatment for other allergies.


Asthma is a chronic, inflammatory condition that causes swelling and blockage in the airways. It can range in severity, and there are several types, depending on the cause and the age at which asthma begins.

Anyone of any age can develop asthma. Women are more likely to develop the condition after the age of 20 years, and smoking and air pollution heavily contribute to the issue. The immune system and asthma share a strong link, and people with asthma often have other allergies.

A young child might find that asthma seems to resolve without treatment but returns in adult life. However, moderate and severe cases often require treatment.

Asthma attacks involve a sudden and severe recurrence of symptoms, and these are how younger children normally experience asthma. Adult-onset asthma tends to be more constant and persistent.

Diagnosing asthma involves testing lung function and immune response, as well as assessing an individual for other condition with similar symptoms to asthma risk of asthma for young children.

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