What Is Asthma? — An Airway That Tightens Too Easily, and the Inflammation That Keeps It Swollen

"Whenever They Catch a Cold, They Wheeze at Night"

About three days after a child catches a cold, their cough worsens every night, and a whistling sound comes from their chest every time they breathe out. At the hospital, you are told it "might be asthma," and you are given two medications to inhale. You are told to use one every day, and the other when you are short of breath.

Adults hear the same thing. When exposed to cold air or climbing stairs, the chest tightens, and a cough lingers for weeks even after a cold heals.

This article follows what asthma does to the pathways where air travels in and out, what each of the two medications does, and why guidelines on how to use those drugs have recently changed.

A Pathway That Tightens All Too Easily

The airway is the system of tubes through which air travels from the nose and mouth deep into the lungs. The bronchi are the tubes formed when the airway descending from the neck splits to enter both lungs and grows progressively narrower. The walls of the bronchi contain muscles that wrap around the tubes, and when these muscles contract, the tubes narrow.

Asthma is a disease in which chronic inflammation persists in the airway, causing the airway to easily narrow in response to triggers and then repeatedly widen again (PMID 12776439, PMID 9298717). Asthma is explained by chronic inflammation of the airway, the property of the airway becoming excessively sensitive, and typically reversible airway obstruction. Roughly 350 million people worldwide suffer from asthma, and among them, 45 to 70% have mild asthma (PMID 33945639).

Inflammation is a reaction in which the body rallies immune cells, causes the area to swell, and responds against stimuli such as injury, infection, or substances introduced from outside the body. In the airway of someone with asthma, this reaction occurs even in response to substances that are harmless to most people (PMID 3276757), and it repeats rather than flaring up just once and passing (PMID 12776439).

Airway hyperresponsiveness is the property whereby the airway narrows more easily and more intensely, even in response to stimuli that cause no trouble for others. The airway is the medical term for the pathway through which we breathe. The airway of a person with asthma reacts at a lower threshold to inhaled, airway-narrowing substances, and narrows more steeply and to a greater degree as the stimulus grows (PMID 12629006). This property is why this article compares asthma to "a pathway that tightens all too easily."

Reversibility is the property whereby a narrowed airway widens again either on its own or through medication that expands the airway. Airway obstruction in asthma is typically reversible, but in some people, it is only partly reversible (PMID 12592297). A disease in which the airway narrows irreversibly is covered in another part of this series, the one addressing What Is COPD? — A Balloon That Won't Empty, and the Breath That Leaves in the First Second.

Wheezing is a high-pitched, whistle-like breathing sound produced as air escapes through a narrowed airway. The symptoms of asthma are wheezing, coughing, shortness of breath, and chest tightness, and these symptoms fluctuate, improving and worsening even in the same person. Because asthma varies greatly and does not remain at the same intensity all the time, guidelines state that how well asthma is controlled should be periodically reassessed (PMID 17983880).

Asthma is a disease in which a sensitive airway repeatedly tightens easily in response to triggers and then relaxes again, underpinned by long-standing inflammation.

The Three Pathways Where the Airway Narrows

There are three pathways by which the asthmatic airway narrows: the muscles in the bronchial wall contract, the wall swells, and too much mucus is produced (PMID 24286679). The narrowing of the airway involves muscle spasms mixed in various proportions with swelling, mucus, and an influx of various inflammatory cells (PMID 12592297). When looking inside the airway of someone with asthma, the muscles have grown thicker, the inside of the wall is swollen, the cells lining the inside of the airway have sloughed off, and the mucus-producing glands are overworked (PMID 12776439).

Therefore, simply relaxing the muscles addresses only one of the three pathways. The swelling, mucus, and underlying inflammation remain untouched (PMID 40250558, PMID 32482150).

Many of the cells that cause inflammation are linked to allergies (PMID 18498538, PMID 12776439). An allergy is an overreaction of the immune system to substances that are harmless to most people. Asthma was once thought to be a purely allergic disease, but our understanding has broadened to include the involvement of damage and repair processes within the cells that make up the airway itself (PMID 18498538). Although asthma often occurs alongside allergies, many asthma patients do not have allergies (PMID 12843993). Asthma that begins in childhood is frequently allergic, whereas asthma that starts later in life is increasingly unrelated to allergies (PMID 31131265).

It is difficult to give a single answer as to why asthma develops in certain people. Multiple genes are involved, and environmental factors such as tobacco smoke, diet, and airway infections are also discussed, but it has been difficult to directly link them as the causes of asthma (PMID 10550729).

When inflammation repeats and cycles through damage and repair, the architecture of the airway can change for the long term (PMID 12776439). Airway remodeling is a change in the very architecture of the airway, such as thickening of the airway wall. Airway remodeling thickens the airway wall, which narrows the airway and increases its sensitivity, and is associated with a poor course of asthma (PMID 19387034). However, the explanation that remodeling stems directly from inflammation is still debated (PMID 19387034), and understanding has recently shifted toward viewing asthma as a disease in which inflammation and airway structure are equally involved (PMID 21636119). Remodeling is thought to lead to irreversible blockage and a decline in lung function (PMID 21636119).

The airway narrows because its muscles tighten, its walls swell, and it fills with mucus. Underlying all of this is the inflammation that triggers those three processes.

What Makes the Airway Tighten

A trigger is what actually makes an already sensitive airway narrow. Cold air, exercise, upper airway infections like a cold, cigarette smoke, and inhaled allergens block the airway (PMID 12776439). Infections, allergens and irritants, and exercise are all counted as triggers that shake up asthma (PMID 12592297).

A virus is a very small germ that cannot multiply on its own and must enter the cell of another living thing to multiply. Among the triggers that call forth an asthma flare-up, the most common is a viral infection of the airway (PMID 28689842). One review notes that viral infections of the upper airway were linked to 80% of asthma flare-ups in children and 50% of asthma symptom appearances in adults (PMID 12619381). Among them, the one most commonly linked is rhinovirus, which causes head colds (PMID 28689842). What colds and the flu do in the airway is covered by another piece in this series, the one dealing with How Do a Cold, the Flu, and Pneumonia Differ? — An Infection That Stays in the Entryway, and One That Reaches the Inner Room.

An asthma flare-up is a time when symptoms become noticeably worse than usual and do not subside with everyday treatment. This is what is commonly called an "asthma attack." No matter how severe an asthma is, and even if treatment is going well, flare-ups can arrive (PMID 28689842). Over top of long-lasting inflammation, contact with allergens, microbes, or air pollutants, or when treatment that suppresses inflammation falls short, sudden worsening piles on top (PMID 18498538).

Allergens do not call forth only that moment's tightening. When people are made to inhale allergens in a lab, an early response arrives within two hours, and in many people, a late response can arrive again between three hours and twelve hours, and the airway also becomes more sensitive (PMID 3276757, PMID 12776439). This added sensitivity is much smaller than the difference between a person with asthma and a healthy person, but it is of a size similar to the changes that occur when asthma is not well controlled (PMID 12629006). Substances breathed in at the workplace also become triggers, so that about one in ten cases of asthma newly arising in adulthood stems from the workplace (PMID 11544449).

Triggers are the triggers that make a sensitive airway tighten, and the most common trigger calling forth asthma flare-ups is a viral infection like a cold.

Tests That Confirm Narrowing and Reversibility

Asthma is not confirmed by the shape of the symptoms alone. Doctors ask about the pattern of symptoms going up and down, and use tests to check whether the airway actually narrows and whether that narrowing is reversible. Diagnosis is made through a doctor's examination and tests.

A pulmonary function test has a person take a deep breath in and then blow out as hard as possible, measuring the volume and speed of the exhaled air. This test is used for children suspected of having asthma and children with repeated coughing or wheezing, and it is checked together with whether the numbers return after inhaling an airway-widening medication (PMID 10829982). How to read the numbers and graphs from the test is covered in "Reading a Spirometry Report — One Point Among Your Peers, Two Graphs Drawn by a Breath".

The airway may appear completely fine on the day of the test. When symptoms resemble asthma but no obstruction is seen, a test measuring how sensitive the airway is becomes particularly useful for diagnosis (PMID 12629006). This test has the person inhale tiny amounts of a substance that tightens the airway to see how easily the airway narrows (PMID 12776439). However, while this test rarely misses asthma, it can also cause a reaction in people who do not have asthma, making it more useful for ruling out that people visiting the clinic currently do not have asthma (PMID 12797503).

Difficulties also vary by age. In young children, wheezing caused by infections must be distinguished from asthma, and in older adults, heart disease and obesity must be distinguished from asthma, while using pulmonary function tests in preschool children is not consistently recommended (PMID 31131265).

Diagnosing asthma is the work of confirming whether the airway narrows, and whether that narrowing reverses.

Two Branches of Inhalers

An inhaler is a device that lets you breathe in medicine so it reaches your airways directly. Asthma inhalers have two main branches, and we look at the other side among the three types of narrowing.

An inhaled corticosteroid is a medicine where you breathe in steroid medication that presses down inflammation, letting it reach your airways directly. A bronchodilator is a medicine that relaxes the muscles surrounding the bronchi to widen narrowed airways. Inhaled corticosteroids reduce airway inflammation, and bronchodilators relax airway muscles (PMID 40250558). The 2007 U.S. guidelines noted that long-lasting asthma requires both a long-term controller medicine and a quick-relief medicine for when symptoms strike, and that among all age groups, the controller medicine with the greatest effectiveness is the inhaled corticosteroid (PMID 17983880).

A reliever is an inhaler medicine used right when you feel short of breath to make breathing comfortable quickly. For decades, asthma treatment relied on inhalers containing just a single fast-acting bronchodilator as a reliever, and anti-inflammatory treatment often did not accompany it (PMID 42444391, PMID 34470194).

Because this medicine makes breathing comfortable right away, people reach for it frequently. One review explains that this convenience causes people to overuse and rely on relievers, while using anti-inflammatory inhalers less, which destabilizes asthma and increases the risk of worsening (PMID 34470194). It is common to find it difficult to use daily medication consistently, and that increases the risk of flare-ups and death (PMID 33945639).

The link between heavy use of quick-opening medicines and asthma death has been reported since the 1990s. A 1996 review noted that greater use of fast-acting bronchodilators is strongly associated with more asthma deaths, and that this does not seem fully explained simply by the fact that people with more severe disease use more medication. The same review noted that this medicine remains essential for emergency treatment of severe attacks and is useful for relieving suddenly appearing symptoms (PMID 8676612). Recent large observational studies also show an association where greater amounts of this medicine used correspond to more deaths (PMID 42444391).

One branch relaxes muscles to make breathing comfortable, and the other branch presses down the inflammation underneath. Quick-opening medicines alone leave the inflammation behind.

The Third Night After a Cold

Let us imagine an adult with asthma catching a cold. We apply what we saw earlier to this scene.

The cold virus is the most common trigger for asthma to worsen (PMID 28689842). While symptoms gradually worsen into a flare-up, both muscle tightening and inflammation grow together in the airway (PMID 42305977). Wheezing begins at night, and he inhales a medicine used when short of breath. A bronchodilator relaxes the airway muscles to make breathing easier (PMID 40250558).

However, among the three prongs, swelling, mucus, and inflammation are not what this drug addresses. One review article viewed this phase, where symptoms progressively worsen, as a "window of opportunity" to promptly use a drug that dampens inflammation. That review explains that when an inhaled steroid reaches the airway as wheezing or symptoms appear, the subsequent chain of inflammation is reduced, lowering the likelihood that the initial symptom will spread into a flare-up (PMID 42305977).

What can be said in this scene extends only up to which side of the airway the two drugs address. Which medicine to use for this person and how to use it are decided together with him by a physician who knows how severe his asthma is and how it has been until now. If repeating the medicine that widens the airway brings no relief, that is a situation treated as an emergency by guidelines, which we will look at later.

What the Guidelines Changed

In 2019, the use of medications for shortness of breath changed in international guidelines. The Global Initiative for Asthma (GINA) (PMID 34667060), which updates its asthma management strategy report every year, recommended that quick-relief bronchodilators alone no longer be used as a standalone reliever that year (PMID 41733139, PMID 34470194). Instead, it put forward symptom relievers that combine anti-inflammatory medication with a quick-opener as the preferred first choice at all treatment steps (PMID 41733139). Anti-inflammatory reliever therapy is a method where an anti-inflammatory drug and a quick-opener are inhaled together when breathlessness occurs, allowing the medication used for shortness of breath to suppress inflammation at the same time. The two drugs may be contained in a single inhaler or used separately in two inhalers (PMID 40250558). International guidelines recommend one of these combinations as the preferred first-choice symptom reliever for adolescent and adult asthma, whether mild or severe, and recently also listed other combinations as alternatives to the quick-opener-only approach (PMID 41804386). This direction was supported by randomized trials showing a substantial reduction in the risk of severe exacerbations (PMID 41804386). Danish guidelines also no longer recommend using quick-openers alone as a standalone treatment for adults (PMID 35023469).

The scale of those trials is as follows. A pooled analysis of trials in adolescents and adults aged 12 and older with mild asthma compared two approaches. In the pooled result from two of those trials (2,997 people), among the group using only a quick-opener, 109 out of 1,000 people experienced exacerbations requiring oral or injectable steroids, compared to 52 out of 1,000 people in the group using a reliever containing an anti-inflammatory drug (high certainty). Compared with the group using daily inhaled steroids, there was little to no difference in such exacerbations (81 per 1,000 in the daily group versus 65 in the combined-reliever group, low certainty). In the same comparison, asthma-related hospitalizations or unscheduled doctor visits may have been reduced (low certainty), and the daily inhaled steroid dose was lower than in the daily-use group (moderate certainty). The authors concluded that this approach is as effective as the daily-use approach. No difference in mortality was confirmed in any comparison. Because death itself was rare, the confidence intervals were wide in the analysis compared with the daily-use group (PMID 33945639). How to read risk in terms of out of 1,000 people is covered in "If the Risk Was Cut in Half, How Many Fewer People Got Sick? — Relative and Absolute Risk".

Along with what is gained, there are also things gained less. In the same analysis, everyday symptom control was slightly better in the group using daily inhaled steroids, but the difference was smaller than the minimum difference a patient would notice (PMID 33945639). In a 1-year trial dividing 3,849 people aged 12 and older with mild asthma into three arms, the percentage of weeks with well-controlled symptoms was higher in the group using daily inhaled steroids than in the group using the combined reliever only when breathless (44.4% versus 34.4%). The as-needed combined-reliever group had better symptom control than the quick-opener-only group. Severe exacerbations were similar between the two groups containing inhaled steroids, and both were lower than in the quick-opener-only group. The daily inhaled steroid dose in the as-needed group was 17% of that in the daily-use group (PMID 29768149).

The approach is not identical across all guidelines. The 2020 US guidelines recommended different combinations depending on the step, and the adoption of this approach was slow in the United States (PMID 41733139). A 2026 paper by an international expert group reported that for moderate-to-severe asthma, the traditional approach of adding a separate quick-opener for shortness of breath to a daily controller inhaler may still be more suitable for certain patients, and noted that one approach should not be applied to everyone but rather tailored to the individual patient (PMID 41335328). The evidence for children is scarcer than for adults. The pooled analysis noted that more research on children under 12 is needed (PMID 33945639), and in a subsequent open-label trial in New Zealand following 360 children aged 5 to 15 with mild asthma previously treated with quick-openers alone for 1 year, asthma exacerbations in the group using the combined anti-inflammatory reliever were 0.23 per person per year, which was lower than the quick-opener-only group (0.41), with similar safety (PMID 41033330). This is a single trial conducted in one country.

Many people feel anxious at the word "steroid." Inhaled steroids are considered to have a more favorable side-effect profile than oral or injectable steroids that spread throughout the entire body. However, inhaled steroids also have specific side effects that are monitored separately, such as those occurring in the airway (PMID 28864055). For systemic steroids spreading throughout the body, cumulative lifetime exposure increases the risk of complications such as weakened bones, diabetes, and high blood pressure, and one review suggests that preventing exacerbations also reduces the need for such steroids (PMID 42305977). People who used the combined anti-inflammatory reliever had less exposure to systemic steroids than those who used only a quick-opener (PMID 33945639). Children's height has been studied separately. Children who used inhaled steroids for more than 12 months grew an average of 0.48 cm less in the first year than those who did not (result of pooling 16 trials), and in one high-quality trial comparing the drug against a placebo, final adult height was an average of 1.2 cm lower. This analysis viewed this as a small difference corresponding to about 0.7% of final height (PMID 26191797). For some patients, treatments called biologic agents can serve as an alternative to oral steroids (PMID 35023469).

Guidelines have shifted toward combining an anti-inflammatory drug even in medications used for shortness of breath. The evidence is based on trials showing a reduction in severe exacerbations, and separate limitations are noted regarding symptom control and evidence in children.

Signs of a Severe Attack

A severe asthma attack that does not respond to repeated use of the usual rescue inhaler is an emergency that must be recognized and treated immediately (PMID 31690381). Difficulty speaking in full sentences is considered a sign suggesting that the airway is severely blocked (PMID 31690381). Bluish lips or fingertips, and confusion or lethargy, are also classified as danger signs by asthma guidelines.

The reason recognizing these signs is important lies in the evidence. Failing to recognize a life-threatening asthma attack and not treating it in time can have devastating consequences (PMID 8050557). A position paper by Latin American experts notes that relying solely on quick-relief medications delays the recognition of life-threatening attacks (PMID 32482150).

Mild asthma is not far removed from this story. While severe asthma carries a high risk of death, those with mild or moderate asthma can also experience flare-ups (PMID 21718577). Guidelines note that even people with few day-to-day symptoms can be at high risk for frequent flare-ups. The same guidelines recommend using a written asthma action plan that outlines daily treatment and how to recognize and respond when asthma worsens (PMID 17983880).

Asthma deaths still occur across all ages. Alongside the severity of the disease, inadequate management of the condition and difficult socioeconomic circumstances are cited as risk factors for death (PMID 12877725). Inadequate treatment and failure to maintain consistent treatment are discussed as the background behind fatal or near-fatal attacks (PMID 8050557). One review called asthma death "a persistent yet preventable death" (PMID 12877725), and a recent review similarly concludes that treatment should shift toward reducing preventable illness and death (PMID 42444391).

Diagnosis is made through a doctor's examination and tests. The signs above describe situations requiring immediate medical attention.

A severe attack that does not respond to repeated use is an emergency that must be recognized and treated immediately, and risk factors for asthma death include failing to receive and maintain proper treatment.

Is Every Wheeze in a Child Asthma?

Wheezing is common in early childhood, and it decreases as a child grows. During the first few years of life, "transient early wheezing" is the most common, and the main reasons are the structural fact that airways are small and viral infections (PMID 11803801). Most lower airway diseases accompanied by wheezing early in life come along with viral infections (PMID 12619381).

For most children, wheezing that comes with lower airway infections at a young age is a mild condition that does not lead to later wheezing or asthma (PMID 11803801). The abstract of this review does not state with a number what percentage that "most" represents. A substantial number of children who wheezed before their first birthday see their symptoms disappear in their second year of life, and as far as is known, children whose symptoms disappear do not wheeze again later (PMID 20008882).

However, looking at the group as a whole, children who wheeze early are more likely to wheeze later on as well. The review suggests that early infection may not be the cause, but rather a marker that reveals children at higher risk (PMID 11803801).

There are children of another type, too. By around age six, there are children whose wheezing already persists continuously, and these children have high allergy markers and a high likelihood of receiving an asthma diagnosis (PMID 11803801). By around age ten, persistent wheezing accompanied by allergies, which leads to an asthma diagnosis, predominates (PMID 11803801). And one review notes that if a preschooler's wheezing repeats and symptoms are not well controlled, it plays a part in growing up with lower lung function into adulthood (PMID 40762612).

Therefore, it is difficult to give a single label to a child's wheezing. In very young children, wheezing caused by infection must be distinguished from asthma (PMID 31131265), and preschool wheezing harbors several different paths within it (PMID 40762612). For this reason, a recent review emphasizes identifying which path a child's wheezing belongs to and tailoring treatment to that child (PMID 40762612). That judgment is made by the physician who examines the child.

Not all wheezing in children becomes asthma, but repeating and uncontrolled wheezing is also not a sign to be brushed off lightly.

Where to Look Next

Which combinations and to what extent drugs that suppress inflammation and drugs that open airways quickly should be used together, and how this approach works in children under 12 years of age, are still being studied (PMID 41733139, PMID 33945639).

How breath moves in and out from the nose to the alveoli can be seen in another piece in this series, "How Do We Breathe? — An Upside-Down Tree, and the Leaves Where Air Meets Blood". What cold viruses do in the airway continues in "How Do a Cold, the Flu, and Pneumonia Differ? — An Infection That Stays in the Entryway, and One That Reaches the Inner Room", how to read a pulmonary function test report continues in "Reading a Spirometry Report — One Point Among Your Peers, Two Graphs Drawn by a Breath", and the narrowing that does not reverse continues in "What Is COPD? — A Balloon That Won't Empty, and the Breath That Leaves in the First Second".

Why testing with a substance that tightens the airway rarely misses asthma, yet also shows a reaction in people who do not have asthma, can be unpacked in "What a Test Actually Tells You — An Introduction to Sensitivity, Specificity, and Pretest Probability". Another disease where the airway in the throat closes during sleep is covered by "Insomnia and Sleep Apnea — The Alarm That Won't Switch Off, the Airway That Closes".

Bronchiolitis, when a baby under two wheezes at the end of a cold, and how it is linked with later asthma, can be found in "Bronchiolitis, RSV and Croup — In a Thin Straw, the Same Swelling Blocks More of the Way".

Source Papers

• "Global Initiative for Asthma Strategy 2021: executive summary and rationale for key changes." (2022) — PMID 34667060 — The GINA strategy report is updated annually based on evidence.
• "Understanding asthma pathophysiology." (2003) — PMID 12776439 — Asthma = chronic airway inflammation + bronchial hyperresponsiveness + lower airway obstruction that is usually reversible, trigger factors (cold air, exercise, viral upper airway infection, tobacco smoke, allergens), muscle hypertrophy, mucosal edema, epithelial shedding, and mucus hypersecretion, with hyperresponsiveness confirmed by provocation tests.
• "Asthma in pregnancy." (1997) — PMID 9298717 — Asthma is a heterogeneous disease characterized by reversible airway obstruction, airway inflammation, and airway hyperresponsiveness.
• "Combination fixed-dose beta agonist and steroid inhaler as required for adults or children with mild asthma." (2021) — PMID 33945639 — 350 million people worldwide and 45–70% have mild disease, poor adherence to regular treatment increases the risk of exacerbations and death, as-needed combination inhaler vs reliever alone: systemic steroid-requiring exacerbations per 1,000 people 109 vs 52 (high certainty), vs regular inhaled corticosteroids 81 vs 65 (low certainty), symptom control is slightly better with the regular regimen but below the minimal clinically important difference, no difference in deaths (rare so confidence intervals are wide), studies in children under 12 and beyond 52 weeks are needed.
• "Airway hyperresponsiveness." (2003) — PMID 12629006 — Hyperresponsiveness = low threshold, steep slope, and large maximum response, useful for diagnosis when obstruction is absent, hyperresponsiveness added by allergens is smaller than the difference between asthmatics and healthy individuals but similar to changes during loss of control.
• "6. Asthma." (2003) — PMID 12592297 — Trigger factors (viruses, allergens, irritants, exercise), obstruction = muscle spasm + edema, mucus, and inflammatory cells, some patients show only partial reversibility (suggesting remodeling).
• "Expert Panel Report 3 (EPR-3)" (2007) — PMID 17983880 — Asthma is highly variable, requiring periodic assessment of control level, persistent asthma requires both long-term controllers and short-acting relievers, inhaled corticosteroids are the most effective long-term controllers across all ages, low daily symptoms may still carry a high risk of frequent exacerbations, written action plan.
• "Asthma pharmacotherapy." (2014) — PMID 24286679 — Asthma is a chronic inflammatory airway disease causing obstruction through bronchoconstriction, edema, and mucus hypersecretion.
• "Pathogenesis of asthma." (2008) — PMID 18498538 — Once considered a purely allergic disease, structural cell injury and repair are also involved, with acute exacerbations superimposed on chronic inflammation due to exposure to allergens, microbes, or pollutants, or insufficient anti-inflammatory treatment.
• "[Intrinsic asthma]." (2003) — PMID 12843993 — Many asthma patients are not atopic.
• "Asthma Across Age: Insights From Primary Care." (2019) — PMID 31131265 — Early onset is atopic, later onset tends to be non-atopic, infectious wheezing in children is distinguished from heart disease and obesity in the elderly, pulmonary function testing is not routinely recommended in preschool children.
• "Genetics of asthma." (1999) — PMID 10550729 — Multiple genes are involved, and environmental factors such as smoking, diet, and viral infections have been discussed, but it has been difficult to link them directly as causes.
• "Remodeling in asthma." (2009) — PMID 19387034 — Remodeling thickens the airway wall, leading to narrowing and hyperresponsiveness, and is associated with poor outcomes, while the origin of inflammation is debated.
• "Remodeling in asthma." (2011) — PMID 21636119 — Remodeling is hypothesized to produce persistent airflow limitation, decline in lung function, and hyperresponsiveness.
• "Virus-induced asthma." (2002) — PMID 12619381 — Viral upper airway infections are linked to 80% of exacerbations in children and 50% of adult asthma presentations, and the majority of lower airway disease with wheezing in infants and toddlers is associated with viral infection.
• "Asthma Exacerbations: Pathogenesis, Prevention, and Treatment." (2017) — PMID 28689842 — Regardless of severity, exacerbations can occur despite optimal treatment, with viruses (especially rhinovirus) being the most common trigger.
• "Allergen-induced airway hyperresponsiveness." (1988) — PMID 3276757 — Early (0–2 hours) and late (3–12 hours) responses and increased hyperresponsiveness following allergen inhalation.
• "Occupational asthma." (2001) — PMID 11544449 — Roughly one in ten cases of adult-onset asthma originates in the workplace.
• "Pulmonary function tests." (1996) — PMID 10829982 — Spirometry and bronchodilator reversibility testing for children with asthma diagnosis, recurrent cough, or wheezing.
• "Indirect airway challenges." (2003) — PMID 12797503 — Direct provocation tests are sensitive but not specific to asthma, so they can be used currently to rule out asthma.
• "Controversies in Allergy: Should I Combine an ICS With a SABA or With Formoterol for Reliever Therapy?" (2025) — PMID 40250558 — Inhaled corticosteroids reduce airway inflammation while bronchodilators relax airway muscles, anti-inflammatory reliever therapy.
• "Stepping Away from the Blue Inhaler in Asthma Management - A Paradigm Shift." (2021) — PMID 34470194 — Decades of prescribing short-acting bronchodilators, the feeling of symptom relief led to overuse, dependence, and underuse of inhaled corticosteroids, causing unstable control and increased exacerbation risk, prompting the 2019 GINA changes.
• "The beta-agonist controversy." (1996) — PMID 8676612 — Strong association between increased use of short-acting bronchodilators and asthma deaths (not fully explained by severity confounding alone), still essential for acute severe attacks.
• "Current perspectives on β2-adrenergic receptor agonists in asthma" (2026) — PMID 42444391 — Large observational studies associate higher usage with increased deaths, trials show as-needed combination therapy reduces severe exacerbations more with no mortality signal, concluding that preventable morbidity and mortality should be reduced.
• "Beta2-agonist and anti-inflammatory combination therapy for asthma rescue: a paradigm shift in asthma care." (2026) — PMID 42305977 — Bronchoconstriction and inflammation coexist beneath the increase in symptoms preceding an exacerbation, the review's logic viewing the symptom-rising phase as a "window of opportunity," lifetime cumulative systemic steroid dose and bone, diabetes, and hypertension complications.
• "As-needed inhaled corticosteroids in asthma: from evidence to implementation." (2026) — PMID 41733139 — GINA 2019 non-recommendation of short-acting bronchodilators alone and priority of as-needed anti-inflammatory relievers at all steps, US NHLBI 2020 has different step-by-step combinations, slow diffusion within the US, the role of new combination therapies remains undetermined.
• "Anti-Inflammatory Reliever Therapy in Asthma: A Review." (2026) — PMID 41804386 — Based on evidence of reduced severe exacerbations in randomized trials, international guidelines prioritize combination reliever therapy across all severities in adolescents and adults.
• "[Asthma treatment in general practice]." (2022) — PMID 35023469 — Danish guidelines: short-acting bronchodilators alone are no longer recommended for adults, and biologic agents are an alternative to oral steroids in some patients.
• "Inhaled Combined Budesonide-Formoterol as Needed in Mild Asthma." (2018) — PMID 29768149 — 3,849 participants in a 52-week double-blind trial, the percentage of well-controlled weeks was higher with regular inhaled corticosteroids (44.4% vs 34.4%), while severe exacerbation rates were similar between the two inhaled corticosteroid-containing regimens.
• "Optimizing the Use of Inhaled Corticosteroid/Long-Acting β2-Agonist Combinations in Patients with Moderate-to-Severe Asthma." (2026) — PMID 41335328 — Since some patients with moderate-to-severe disease still fit the traditional approach, tailored treatment per patient is recommended.
• "Budesonide-formoterol versus salbutamol as reliever therapy in children with mild asthma (CARE)" (2025) — PMID 41033330 — Open-label trial of 360 children aged 5–15 in New Zealand for 52 weeks, combination reliever group had fewer exacerbations (0.23 vs 0.41/year), with similar safety.
• "Tracheobronchopathy From Inhaled Corticosteroids." (2017) — PMID 28864055 — Inhaled corticosteroids have a more favorable side-effect profile than systemic corticosteroids.
• "Impact of Inhaled Corticosteroids on Growth in Children with Asthma" (2015) — PMID 26191797 — First-year growth velocity reduction of −0.48 cm/year in children treated for over 12 months, final height reduction of −1.2 cm in one high-quality trial, about 0.7% of final height.
• "Acute severe asthma (status asthmaticus)." (2019) — PMID 31690381 — Severe asthma unresponsive to repeated bronchodilator use is an emergency requiring immediate recognition and treatment, and difficulty speaking is a sign suggesting severe airflow obstruction.
• "Near-fatal asthma." (1994) — PMID 8050557 — Failure to recognize and treat life-threatening attacks leads to disastrous outcomes, with lack of appropriate treatment and poor compliance discussed as contributing background factors.
• "Position statement: asthma in Latin America." (2021) — PMID 32482150 — Over-reliance on short-acting bronchodilators delays the recognition of life-threatening attacks.
• "Asthma in adults." (2010) — PMID 21718577 — Severe disease increases mortality risk, and mild-to-moderate disease also carries exacerbation risk.
• "Asthma deaths; persistent and preventable mortality." (2003) — PMID 12877725 — Deaths persist across all ages, with risk factors being disease severity, poor disease management, and difficult psychosocial circumstances.
• "Epidemiology of asthma and recurrent wheeze in childhood." (2002) — PMID 11803801 — Transient early wheezing in early life is predominant (small airways and viruses), the majority of infection-associated wheezing episodes in young children represent a benign state unrelated to subsequent wheezing and asthma, and persistent phenotypes around age 6 have high allergy markers and a high likelihood of asthma diagnosis.
• "Phenotypic differences between pediatric and adult asthma." (2009) — PMID 20008882 — A substantial proportion of wheezing in the first year of life disappears by the second year, and children in whom it disappears do not wheeze again, as far as is known.
• "Phenotype-Based Management of Recurrent Preschool Wheezing and Asthma." (2025) — PMID 40762612 — Preschool wheezing has multiple phenotypes, and recurrent exacerbations and poor control are associated with low lung function trajectories into adulthood.