1. Ada
  2. Conditions
  3. Asthma

Asthma

  1. What is asthma?
  2. Symptoms
  3. Causes
  4. Risks

What is asthma?

Asthma is an inflammatory condition which affects the airways in the lungs. It is one of the most common non-contagious diseases, affecting around 235 million people globally, according to the World Health Organization.[1] The condition can affect men, women and children of all ages. It usually first develops in childhood, but can also appear for the first time in adults.

Asthma primarily affects the bronchial tubes in the lungs, called the airways. During an asthma attack, in which symptoms of asthma flare up, people typically experience breathing difficulties, due to the inflammation of the airways, which results in reduced airflow into the lungs. Asthma can vary in severity; its symptoms may be present every day or only during an asthma attack. The most common symptoms of asthma include wheezing, chest pain and shortness of breath.[1][2]

The reasons why some people develop asthma and others do not are not yet fully medically understood, but there is believed to be a strong genetic component. When asthma develops, it is believed to be due to inhaling irritants in the air, causing an allergic reaction in the airways.

Air pollution, pollen and allergens in the air are some of the most common irritants which cause a person to develop asthma and/or can act as triggers for asthma attacks. A person may find that the triggers of their asthma attacks change over time. Triggers of asthma in childhood may cease to cause symptoms in adulthood, for example.[3]

With effective treatment, asthma occurring at any age can be managed effectively so as to reduce its impact on a person’s quality of life. Treatment of asthma involves learning about and minimizing contact with one’s triggers and the use of medications as needed to relieve ongoing symptoms and to treat asthma attacks. These medications are often inhaled directly into the lungs in the form of a vapour with the use of nebulizers or inhalers,two devices which are easy to use and designed for this purpose.

Symptoms of asthma

Typical symptoms of asthma include:[1][2]

  • Wheezing
  • Coughing
  • Chest tightness
  • Shortness of breath

Usually, these symptoms will be:[2]

  • Recurrent
  • At their most severe first thing in the morning and/or at night
  • Present, or worse, in relation to particular activities, i.e. after contact with a trigger, such as tobacco smoke or exercising

If you think that you or a loved one may be experiencing symptoms of asthma, get a free assessment with the Ada app.

Asthma can affect a person to varying degrees of severity, which is medically assessed according to factors such as:[4]

  • The frequency with which symptoms appear
  • Their impact on a person’s ability to carry out their daily routine and live a good quality of life
  • The impact of the asthma on their lung function, measured with lung function tests
  • The speed at which they can exhale air, a measurement called peak flow

To keep track of their symptoms, people affected by asthma usually carry out peak flow tests, also called peak expiratory flow or PEF tests, twice daily, using a peak flow meter. This is a portable handheld device which allows a person to notice changes in their respiratory function, anticipate flare ups and thereby preventively use medication if needed. For more information about tests which measure a person’s lung function and peak flow, see the ‘Diagnosis’ section.

In adults and children over 12 years of age, asthma severity is classified according to the following criteria:[5]

Intermittent asthma

Also called mild intermittent asthma, this is the least severe form of the condition.

People with intermittent asthma experience:[5][6]

  • Symptoms, such as coughing and wheezing around twice per week or less, with nighttime awakenings due to symptoms occurring twice a month or less
  • Normal lung function between flare ups, with a retention of 80 percent or more of their normal lung function when asthma is active
  • A peak flow score which never varies to a level of more than 20 percent less than their normal score, when asthma is inactive

Intermittent asthma generally causes no symptoms or interference with a person’s day-to-day activities between flare ups, and those affected should be able to attend work or school, and exercise as normal.[5]

People with intermittent asthma tend to have only a few triggers. These are likely to be triggers which are not encountered every day or throughout the year, i.e. seasonal triggers, such as pollen. Bouts of wheezing and coughing, which are otherwise absent, may also develop when the function of a person’s respiratory system is otherwise compromised, i.e. due to a chest infection.[6]

Mild persistent asthma

People with mild persistent asthma experience:[5]

  • Symptoms such as coughing and wheezing more than two days per week, but not every day, and may wake up in the night due to coughing and shortness of breath three or four times per month
  • Normal lung function between flare ups, with scores of 80 percent or more of normal lung function test values when asthma is active
  • A peak flow score which varies between 20 and 30 percent less than their normal score, depending on asthma’s activity

When symptoms occur, or around a flare up, mild persistent asthma may cause minor limitations on a person’s ability to carry out their routine as normal, for example, they may tire more easily during the working day or lack their usual stamina while playing sports. Symptoms may increase with activity.[7]

Moderate persistent asthma

People with moderate persistent asthma experience:[5]

  • Symptoms such as coughing, wheezing and breathlessness daily, with nighttime awakenings due to symptoms more than once per week, but not every night
  • Lung function test results of between 60 and 80 percent of normal lung function test values
  • A peak flow score of more than 30 percent variability

People with moderate persistent asthma are likely to find that flare ups are exercise induced and affect their activity levels, decreasing their capacity for physical exercise and sometimes necessitating time off work or school.[8]

Severe persistent asthma

People with severe persistent asthma experience:[5]

  • Symptoms, such as coughing, wheezing and breathlessness daily, with nighttime awakenings due to symptoms nearly every night
  • Lung function test results of less than or equal to 60 percent of normal values
  • A peak flow score of more than 30 percent variability

Being affected by severe persistent asthma can have a significant impact on a person’s quality of life, as it can be difficult to control, with the airways often being or becoming too inflamed for typical treatment approaches to work well. Devising an effective treatment or management plan with one’s doctor can therefore be an ongoing process, particularly if there are many different triggers that need to be identified. Until an effective treatment plan is devised, asthma symptoms will significantly reduce the activity levels and quality of life of the affected person.

Asthma, which was previously mild or moderate, may become severe over time. It is not known why some people develop severe persistent asthma and others do not, but this form of the condition is more likely to affect those with a previous diagnosis of asthma than the general population.[9] The 2016 Global Initiative for Asthma (GINA) guidelines make a point of differentiating between severe and poorly controlled asthma: persistent asthmatic symptoms may be caused by an ineffective treatment approach, rather being an indicator, or the result of having, a particularly severe case of asthma.[10]

Symptoms of an asthma attack

During an asthma attack, symptoms of asthma worsen for a short time. In the body, an asthma attack is caused by swelling of the bronchial tubes, causing a sudden narrowing of the airways, which prevents air from entering the lungs.

Early warning signs of an asthma attack include:[11]

  • Worsening of asthma symptoms, particularly coughing and shortness of breath
  • Needing to use medication that provides quick relief from symptoms more often than normal
  • Finding that the duration for which quick relief medications provide relief from symptoms is shorter than normal, i.e. less than four hours[12]
  • Becoming tired more quickly after activities, especially exercise

During an asthma attack, a person may experience some or all of the following symptoms:[2][11]

  • Regular symptoms of asthma ‒ wheezing, coughing and breathlessness ‒ may become more intense, and/or constant
  • Tightening of the neck and chest muscles; retractions
  • A rattling sound in the chest
  • Increased heart rate
  • Feeling faint or fainting
  • Breathlessness, which can lead to difficulties eating, speaking or sleeping
  • Feelings of anxiety or panic
  • Pale face
  • Blue fingers or lips
  • Sweating
  • Drowsiness
  • Exhaustion
  • Confusion
  • Dizziness

The duration of an asthma attack may vary, depending on how inflamed a person’s airways are, and how long they have been inflamed for. Asthma attacks can last a few minutes, or in more severe cases, hours or days. A mild asthma attack may get better on its own or with medication, while a more severe asthma attack may require medical attention to bring symptoms under control.

All people with asthma will have clear written instructions, called an asthma action plan, which provides advice on how to manage asthma generally, as well as during an asthma attack. When an asthma attack occurs, a person should follow their action plan and seek emergency medical attention if symptoms do not clear up as expected. For advice on treating an asthma attack, see the ‘Treatment’ section of this resource.

Symptoms of asthma in children

Asthma affects around 6.2 million children in the U.S.[13] If a child experiences recurrent coughing, wheezing, tightness or pain in their chest, or shortness of breath, it is important to consult a doctor, as one or more of these symptoms may indicate childhood-onset asthma.

As with adults, the most common signs of asthma in children include:[2]

  • Wheezing
  • Chest pain
  • Shortness of breath

These symptoms may be present every day or only during an asthma attack.

Asthma can cause acute discomfort and can have a debilitating effect on the child’s overall health, including symptoms like tiredness, depleted strength and recurrent coughing.

Possible warning signs and symptoms of childhood-onset asthma include:

  • Wheezing
  • Chest pain
  • Chest tightness
  • Depleted stamina after play or exercise
  • Diminished energy throughout the day
  • Difficulty drawing breath
  • Recurrent coughing, typically at night
  • Retractions, i.e. involuntary pulling-in of the chest which occurs as a result of labored breathing
  • Shortness of breath

Children are affected by asthma more commonly than adults. Asthma in children usually starts to develop in early childhood, often before the age of five. Despite the presence of asthma-like symptoms, it can be difficult to diagnose asthma in infants and young children, as their lungs may not be developed sufficiently to carry out certain tests. Are you worried that your child, or a child that you know, may be experiencing symptoms of asthma? Get a free symptom assessment by downloading the Ada app.

The potential impact of childhood-onset asthma on a child’s quality of life and long-term health can be significantly minimized by identifying appropriate treatment methods to bring their symptoms under control. Children with untreated asthma tire more easily after exercise than their peers and are prone to coughing and wheezing.

With effective treatment, it is possible to reduce the symptoms of asthma, so that asthmatic children can carry out their day-to-day activities as normal, including participating in exercise and outdoor activities. For more information, see this resource on asthma in children.

Symptoms of asthma in toddlers and babies

Symptoms of asthma in toddlers and babies may include:[14]

  • Wheezing
  • Fast or labored breathing
  • Difficulties eating and drinking as normal, including breast or bottle feeding
  • Breathlessness, particularly when this is exercise-induced, i.e. during play
  • Fatigue, which may manifest as a lack of interest in normal activities
  • Pallor; pale colouring in the face, and/or blue lips and fingers

At least half of children who are diagnosed with asthma show the first signs of developing the condition before the age of five.[14] The most common sign is developing a respiratory infection in the lungs, at which point medical attention should be sought in order to establish the cause of the problem. Children under five are more prone to respiratory infections than the general population, there are therefore many other common conditions which their possibly asthmatic symptoms could relate to, including bronchitis, croup or epiglottis, rendering a medical assessment essential.

Causes of asthma

The symptoms of asthma are caused by the swelling of the airways, which makes them temporarily narrow, reducing airflow to and from the lungs.

It is not always possible to identify the reasons why a person has developed asthma, and it is possible to develop the condition with no apparent trigger. The main causes of asthma are believed to include:[15]

  • Genetic predisposition. People with asthma, eczema, hives and/or allergic rhinitis, or a family medical history of these conditions, are more likely to develop asthma than those without.
  • Environmental factors. Inhaling certain particles in the atmosphere can cause a person to develop asthma. These include dust mites, pollen and pet dander, as well as air pollutants such as smoke from tobacco products.
  • Infections which affect the airways. Viral infections, such as the viruses which cause the common cold, can cause asthma to develop in some people.

Research suggests that growing up in an urbanised area makes people more likely to develop asthma, based on studies comparing the prevalence of the condition in rural environments, compared to more built-up areas. The reasons for this are not yet fully understood, but are thought to relate to higher levels of pollution in urbanized areas, in combination with the fact that rural environments are believed to provide children with certain protective effects against developing asthma.[16] This is known as the hygiene hypothesis.

The hygiene hypothesis

Also known as biome depletion theory, or lost friends theory, the hygiene hypothesis is the proposition that increased exposure to particular infectious agents such as bacteria, viruses and parasites has beneficial effects on the development of the immune system.[17]

Exposure to a wider variety of germs at a young age as a result of being raised in a rural area or a large family, compared to being an only child, or being a child raised in a cleaner, urban environment, is believed to help teach the developing immune system to differentiate effectively between harmful and harmless substances. Therefore, according to the hygiene hypothesis, substances such as pet dander, which may trigger the development of asthma, may be less likely to cause inflammation of the airways and the development of asthma in a child who grew up in a rural area or a larger family, with exposure to more germs, than in an only child or one who grew up in a more hygienic urban area.

The hygiene hypothesis is not universally medically accepted. An important reason for this is that exposure to certain viruses, for example respiratory syncytial virus (RSV), is believed to increase the likelihood of a child developing asthma.[18] Furthermore, it is impossible to predict accurately whether a child will develop asthma or not. Efforts to expose a child to germs ‒ such as one might encounter on a farm ‒ in order to help develop their immune system are therefore not recommended. Not only is this likely to trigger asthma in children predisposed to the condition, but it also increases the possibility of developing other harmful diseases and infections.

Triggers of asthma

In people who are predisposed to develop asthma, the swelling of the airways occurs in relation to exposure to certain triggers. The triggers which cause asthma symptoms to appear or worsen vary greatly between people. Over time, a person may grow out of developing an asthmatic response to certain triggers or find that they have developed new triggers. Triggers of asthma may cause asthma to develop in the first place, as well as causing asthma symptoms to flare up in people already affected by the condition.

Asthma attacks or symptoms can be triggered by a very wide variety of different factors including:[19][20][21][22][23][24][25]

  • Respiratory infections; such as colds and flu, which inflame the airways
  • Exercise; the changes to the way a person breathes when they exercise can serve to trigger asthma symptoms
  • Allergens; asthma can be triggered by allergies to seasonal irritants like pollen, perennial irritants like dust mites, pet dander and, if the affected person has a food allergy, certain foods
  • Molds and fungi, due to the spores they release into the air, which can be inhaled
  • Outdoor irritants, such as pollution, fumes and smoke
  • Indoor irritants, such as cleaning and decorating products, solvents, dust, carpeting and dust-containing air from ventilation systems
  • Alcohol; either all alcoholic drinks or certain types; in some cases asthma symptoms may be triggered by commonly added chemicals like histamine and sulfites rather than the alcohol itself
  • Smoke from tobacco products; smoking can make asthma worse over time by causing permanent lung damage. Even second-hand smoke can trigger asthma symptoms
  • Medications, especially beta-blockers, pain relievers like aspirin and non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen and medications used to treat hypotension and heart disease, called Angiotensin-converting enzyme (ACE) inhibitors
  • Emotions, in particular, stress, laughter and distress
  • Hormonal changes in women; the fluctuations in hormonal levels that occur during menstruation, pregnancy and menopause are all possible triggers of asthma
  • Weather, in particular, changes from hot to cold, and thunderstorms, due to the increased moisture in the air

Good to know: There are several types of asthma which are associated with certain kinds of triggers, for example:

  • Allergic asthma is a type of asthma which is triggered by allergens, in people affected by allergies
  • Exercise-induced asthma is asthma, which only occurs when the affected person exercises
  • Occupational asthma is a type of asthma caused by irritant particles encountered in the workplace, for example from cleaning products, fumes, smoke, cereal dust or flour

Occupations which carry a high risk of being exposed to irritant particles which can trigger asthma include:

  • Firefighters
  • Chemical workers
  • Those involved in food preparation or processing
  • Hospital staff
  • Painters and builders
  • Animal handlers
  • Agricultural workers

Risk factors for developing asthma

There are certain factors which increase a person’s risk of developing asthma. These include:[26][27][28]

  • Being affected by an atopic condition, such as eczema (atopic dermatitis), allergic rhinitis or hay fever
  • Having family members or a family medical history of atopic conditions
  • Exposure to smoke from tobacco products; this includes using them oneself, second-hand smoke and being exposed to tobacco smoke as a young child and/or before birth due to their mother smoking in pregnancy
  • Exposure to irritant particles as a result of one’s job
  • Living in a highly polluted area
  • Getting respiratory infections, such as bronchitis, as a child; due to conflicting scientific findings, it is currently unclear whether these kinds of infections are causative of, or protective against, asthma
  • Being obese, which increases the likelihood of inflammation developing within the body, including in the airways

The risk of asthma associated with a person’s biological sex depends on their age. In childhood, boys are more likely to develop asthma than girls, whereas in adulthood, women are more likely to develop asthma than men. This is thought to be explained, in part, by the hormonal fluctuations which women experience due to their menstrual cycle.[27]


  1. Asthma.” World Health Organization. 2018. Accessed: 15 October 2018.

  2. Asthma: symptoms.” NHS Choices. 19 February 2018. Accessed: 15 October 2018.

  3. Patient education: asthma symptoms and diagnosis in children (beyond the basics.” UpToDate. 2018. Accessed: 15 October 2018.

  4. Categorizing asthma severity: an overview of national guidelines.” Clinical Medicine and Research. August 2004. Accessed: 14 October 2018.

  5. Expert Panel Report 3: Guidelines for the Diagnosis and Management of Asthma--Summary Report 2007.” National Asthma Education and Prevention Program. 2007. Accessed: 15 October 2017.

  6. Living with mild intermittent asthma.” Health Union. 13 February 2018. Accessed: 15 October 2018.

  7. Physical effects of asthma.” University of Illinois Hospital & Health Sciences System. 2018. Accessed: 15 October 2018.

  8. Living with moderate to severe persistent asthma.” Genentech. 2018. Accessed: 15 October 2018.

  9. What is severe asthma?.” Asthma U.K. October 2016. Accessed: 15 October 2018.

  10. Asthma guidelines.” Medscape. 08 January 2019. Accessed: 17 January 2019.

  11. Asthma attack.” American College of Allergy, Asthma and Immunology. 2014. Accessed: 15 October 2018.

  12. Asthma attacks.” Asthma U.K. 2018. Accessed: 15 October 2018.

  13. Asthma facts.” United States Environmental Protections Agency. May 2017. Accessed: 15 October 2018.

  14. Asthma in infants.” Asthma and Allergy Foundation of America. 2017. Accessed: 15 October 2018.

  15. Asthma: causes.” NHS Choices. 19 February 2018. Accessed: 15 October 2018.

  16. Urbanisation, asthma and allergies.” Thorax. September 2011. Accessed: 15 October 2018.

  17. Hay fever, hygiene and household size.” British Medical Journal. 1989. Accessed: 16 October 2018.

  18. Evidence for a causal relationship between respiratory syncytial virus infection and asthma.” Expert Review of Anti-Infective Therapy. 2012. Accessed: 16 October 2018.

  19. Asthma Triggers.” Asthma U.K. 2018. Accessed: 16 October 2018.

  20. Medications may trigger asthma symptoms.” American Academy of ASthma and Immunology. 2018. Accessed: 16 October 2018.

  21. The unresolved relationship of alcohol and asthma.” The International Archives of Allergy and Immunology. 2016. Accessed: 16 October 2018.

  22. Asthma.” Patient. 08 November 2016. Accessed: 16 October 2018.

  23. Female hormones may be linked to asthma, study suggests.” Science Daily. 15 February 2018. Accessed: 16 October 2018.

  24. Common asthma triggers.” Centers for Disease Control and Prevention. 14 December 2010. Accessed: 16 October 2018.

  25. What causes or triggers asthma?.” Asthma and Allergy Foundation of America. 2017. Accessed: 16 October 2018.

  26. Asthma in preschool children: prevalence and risk factors.” Thorax. 2001. Accessed: 16 October 2018.

  27. Asthma.” National Heart, Lung and Blood Institute. 2014. Accessed: 16 October 2018.

  28. Asthma: epidemiology, etiology and risk factors.” Canadian Medical Association Journal. October 2009. Accessed: 16 October 2018.