Though asthma is common, what causes it isn’t fully understood. It’s likely there is a genetic component that predisposes a person to develop the disease, but typically certain environmental factors must also be in place.

But although experts may not know for sure why one person has asthma and another doesn’t, they do understand the changes in the body that lead to asthma symptoms—bronchoconstriction (narrowing of the bronchi, or airways) and excess mucus production that together restrict airflow.

There also are a variety of known risk factors for asthma, such as excess weight, as well as many common triggers ranging from allergens like dust mites and mold to exercise and respiratory infections such as a common cold.1

This article describes what’s currently known about the risk factors for asthma.

Inhaling through nebulizer at doctor's office!

Risk Factors for Asthma

You are at an increased risk of having asthma if you:2

Have a family history of asthma
Had certain types of viral respiratory infections as a baby or young child
Have eczema (atopic dermatitis) or allergies, such as hay fever (allergic rhinitis)
Are exposed to dust or chemical fumes in your work
Currently smoke or did in the past, your mother smoked while pregnant with you, or you’ve been exposed to secondhand smoke
Have been exposed to air pollution (specifically ozone)
Are overweight, which can lead to worse symptoms and less effective control of the condition3
Were born prematurely or had a low birth weight4

Among children, asthma is more common in males than females. By adulthood, this is reversed, and females are more likely to have asthma.5

Asthma Disparities

Racial and ethnic minority groups experience a disproportionate burden of asthma. Black and Latinx people and American Indian/Alaska Natives are more likely to develop asthma compared to White Americans. Puerto Ricans have particularly high rates of asthma, nearly twice that of non-Hispanic Whites.6

Black Americans are five times more likely to be hospitalized for asthma compared to White Americans, and three times as likely to die from it. Black women have the highest risk of death from asthma of all groups.7

The reasons for these disparities are varied and include less access to health care, poorer quality care, increased exposure to indoor and outdoor triggers, and higher levels of stress.

Atopic March

Infants who have atopic dermatitis sometimes go on to develop hay fever and asthma—especially if they experienced wheezing as babies. This phenomenon is referred to as atopic march or progressive atopy.

It’s thought that the barrier that skin usually provides against allergy-triggering substances (allergens) is less effective in children with eczema, allowing them to become sensitized.8

Genetics

It is well-established that asthma runs in families, which suggests that the condition has a significant genetic component. More than 100 genes have been associated with allergic asthma,9 most of which are involved in immune reactions and lung functions.

However, the presence of any of these genes in a person’s DNA does not guarantee they will have asthma; it only means they’re at an increased risk. It typically requires exposure to an environmental trigger for asthma to develop.

You are three to six times more likely to have asthma if one of your parents has asthma, according to the American Lung Association.2

Asthma Triggers

The potential causes of asthma symptoms and asthma attacks in those who have the condition are as variable and unique to each individual as are the factors that put them at risk in the first place. There’s a wide variety of such triggers, and many people have more than one.

Indoor Triggers

Your home may harbor any of several common allergens known to bring on asthma symptoms.

Dust mites: Dust mites (Dermatophagoides pteronyssinus) are microscopic insects that exist in every home and feed on tiny flakes of skin and hair found on bedding (mattresses, pillows, bed covers), carpets, upholstered furniture or anything covered in fabric, and stuffed toys.10
Mold: Mold is most often found on wet or damp surfaces in bathrooms, kitchens, and basements.
Cockroaches and other pests: Body parts, urine, and droppings of cockroaches and pests contain proteins that can trigger allergy symptoms.11
Pets: Allergens from your pets’ dead skin, droppings, urine, and saliva can trigger asthma.
Secondhand smoke: Environmental tobacco smoke contains more than 250 different chemicals, including benzene, vinyl chloride, and arsenic, that may irritate airways and bring on asthma symptoms.
Nitrogen dioxide: Nitrogen dioxide is a gas released by gas stoves, fireplaces, and gas space heaters. It can irritate lungs and lead to shortness of breath.12

Outdoor Triggers

During the spring and fall, airborne pollens and molds commonly trigger asthma symptoms, among them:

Pollen: Pollens are small, powdery granules that are essential for plant fertilization. Pollens from many different kinds of grasses, weeds, and trees may trigger allergy and asthma symptoms. The season and weather conditions greatly influence the amount of pollen in the air. Pollen season varies depending on location but typically lasts from February to October.
Mold: Mold growing in soil or on outdoor vegetation can become airborne and trigger asthma symptoms.
Weather: Certain weather conditions can make asthma triggers more problematic. Pollen is particularly plentiful when it’s hot, dry, and windy outside, for example. Mold thrives in rainy or humid weather. Dry, cold, or windy weather can also set off asthma episodes.

Respiratory Infections

Any type of respiratory infection—such as a common cold or the flu—can trigger asthma symptoms.13 If you have asthma, it’s especially important to take measures to stay well:

Wash your hands frequently
Don’t touch your nose or mouth while you’re out in public or around someone who’s sick
Get a flu shot every year.

Less Common Asthma Triggers

Although these triggers are relatively uncommon, they are potentially serious for people who are sensitive to them.

Medications: A number of different medications are associated with asthma flare-ups, including pain medications (aspirin, ibuprofen, naproxen) and beta-blockers.14
Food allergies: Some foods like fish, soy, eggs, wheat, and tree nuts are common food allergens. In some patients with life-threatening food allergies, eating these foods can also trigger asthma attacks, which can be deadly.
Exercise: Wheezing, coughing, and chest pain can occur in response to physical activity in people with asthma. This is known as exercise-induced bronchoconstriction (EIB) and is most common in teens and young adults.

What are risk factors and causes of asthma?

Asthma results from complex interactions between an individual’s inherited genetic makeup and interactions with the environment. The factors that cause a genetically predisposed individual to become asthmatic are poorly understood. The following are risk factors for asthma:

Family history of allergic conditions
Personal history of hay fever (allergic rhinitis)
Viral respiratory illness, such as respiratory syncytial virus (RSV), during childhood
Exposure to cigarette smoke
Obesity
Lower socioeconomic status
Exposure to air pollution or burning biomass

What are the different types of asthma?

Asthma may not be the same in different affected individuals. Asthma specialists currently use a variety of clinical data to categorize a patient’s asthma. This data includes the age of asthma onset, the presence or absence of environmental allergies, the presence or absence of elevated blood or sputum levels of eosinophils (a type of white blood cell), lung function testing (spirometry and fractional excretion of nitric oxide), obesity, and cigarette smoke exposure.

Types: T2 high or non T2 (T2 low)

Your doctor may refer to asthma as being “allergic” or “eosinophilic.” One or both of these characteristics make up a “T2 high” phenotype of asthma, which is the term for the type of immune inflammation associated with asthma. The allergic type typically develops in childhood and is associated with environmental allergies, which approximately 70%-80% of children with asthma have. Typically, there is a family history of allergies. Additionally, other allergic conditions, such as food allergies or eczema, are often also present. Allergic asthma often goes into remission in early adulthood. However, in many cases, asthma reappears later. Sometimes allergic asthma can appear with elevated blood or sputum eosinophils. Asthma that develops in adulthood may be associated with sputum or blood eosinophils but without environmental allergies. Sometimes patients in this category also have nasal polyps, which are eosinophil-rich growths in the nasal lining.

Non T2 asthma, or T2 low asthma, comprises a smaller yet difficult-to-treat proportion of asthma that is not associated with allergies or eosinophils. This type of asthma is sometimes called “neutrophilic asthma” and may be associated with obesity.

What are asthma symptoms and signs?

The classic signs and symptoms of asthma are shortness of breath, cough (often worse at night), and wheezing (high-pitched whistling sound produced by turbulent airflow through narrow airways, typically with exhalation). Many patients also report chest tightness. It is important to note that these symptoms are episodic, and individuals with asthma can go long periods without any symptoms.

Common triggers for asthmatic symptoms include exposure to allergens (pets, dust mites, cockroaches, molds, and pollens), exercise, and viral infections. Other triggers include strong emotions, odor exposure, and temperature extremes. Tobacco use or exposure to secondhand smoke complicates asthma management.

Many of the symptoms and signs of asthma are nonspecific and can be seen in other conditions as well. Symptoms that might suggest conditions other than asthma include new symptom onset in older age, the presence of associated symptoms (such as chest discomfort, lightheadedness, palpitations, and fatigue), and lack of response to appropriate medications for asthma.

The physical exam for asthma is often completely normal. Occasionally, wheezing is present. In an asthma exacerbation, the respiratory rate increases, the heart rate increases, and the work of respiration increases. Individuals often require accessory muscles to breathe, and breath sounds can be diminished. It is important to note that the blood oxygen level typically remains fairly normal even in the midst of a significant asthma exacerbation. Low blood oxygen level is therefore concerning for impending respiratory failure.

How do doctors diagnose asthma?

The diagnosis of asthma begins with a detailed history and physical examination. Primary-care providers are familiar with the diagnosis of asthma, but specialists such as allergists or pulmonologists may be involved. A typical history is an individual with a family history of allergic conditions or a personal history of allergic rhinitis who experiences coughing, wheezing, and difficulty breathing, especially with exercise, viral infections, or during the night. In addition to a typical history, improvement with a trial of appropriate medications is very suggestive of asthma.

In addition to the history and exam, the following are diagnostic procedures that can be used to help with the diagnosis of asthma:

Lung function testing with spirometry: This test measures lung function as the patient breathes into a tube. If lung function improves significantly following the administration of a bronchodilator, such as albuterol, this essentially confirms the diagnosis of asthma. It is important to note, however, that normal lung function testing does not rule out the possibility of asthma.
Measurement of exhaled nitric oxide (FeNO): This can be performed by a quick and relatively simple breathing maneuver, similar to spirometry. Elevated levels of exhaled nitric oxide are suggestive of T2 inflammation seen in some types of asthma.
Skin testing for common aeroallergens: The presence of sensitivities to environmental allergies increases the likelihood of asthma. Of note, skin testing is more accurate than blood work (in vitro testing) for environmental allergies. Testing for food allergies is not indicated in the diagnosis of asthma.
Doctors often perform blood tests for the allergic antibody (IgE) and eosinophils to establish the presence of T2 high asthma.
Other potential but less commonly used tests include provocation testing such as a methacholine challenge, which tests for airway hyperresponsiveness. Hyperresponsiveness is the tendency of the breathing tubes to constrict or narrow in response to irritants. A negative methacholine challenge makes asthma unlikely. Specialists sometimes also measure sputum eosinophils, another marker for “allergic” inflammation seen in asthma. Chest X-rays or CT scans may show hyperinflation, but are often normal in asthma. Tests to rule out other conditions, such as cardiac testing, may also be indicated in certain cases.

What are asthma treatment options? Are there home remedies for asthma?

The treatment goals for asthma are to:

adequately control symptoms,
minimize the risk of future exacerbations,
maintain normal lung function,
maintain normal activity levels, and
take the least amount of medication possible with the least amount of potential side effects.

Inhaled corticosteroids (ICS) are the most effective anti-inflammatory agents available for the chronic treatment of asthma and are first-line therapy per most asthma guidelines. It is well recognized that ICS are effective in decreasing the risk of asthma exacerbations. Furthermore, the combination of a long-acting bronchodilator (LABA) and an ICS has a significant additional beneficial effect on improving asthma control. Short-acting rescue inhalers are the standard of care for breakthrough symptoms.

The most commonly used asthma medications include the following:

Short-acting bronchodilators (albuterol [Proventil, Ventolin, ProAir, ProAir RespiClick, Maxair, Xopenex]) provide quick relief for symptoms occurring despite controller medications. These may also be used alone in patients with occasional symptoms or patients experiencing symptoms with exercise only. Inhaled steroids (budesonide [Pulmicort Turbuhaler, Pulmicort Respules], fluticasone [Flovent, Arnuity Ellipta, Armon Air RespiClick], beclomethasone [Qvar], mometasone [Asmanex], ciclesonide [Alvesco], flunisolide [Aerobid, Aerospan]) are first-line anti-inflammatory therapies.
Long-acting bronchodilators (salmeterol [Serevent], formoterol [Foradil], vilanterol) can be added to ICS as additive therapy. LABAs should never be used alone for the treatment of asthma.
ICS/LABA combination agents combine corticosteroids and long-acting bronchodilators. Fluticasone/salmeterol (Advair, AirDuo, Wixela), budesonide/formoterol (Symbicort), fluticasone/vilanterol (Breo), mometasone/formoterol (Dulera).
Leukotriene modifiers (montelukast [Singulair], zafirlukast [Accolate], zileuton [Zyflo]) can also serve as anti-inflammatory agents.
Anticholinergic agents or antimuscarinic agents (ipratropium [Atrovent, Atrovent HFA], tiotropium [Spiriva], umeclidinium [Incruse Ellipta]) can help decrease sputum production.
There is one triple combination agent of an inhaled corticosteroid, long-acting bronchodilator, and anti-muscarinic agent: fluticasone/vilanterol/umeclidium (Trelegy) that is most often used for asthma/COPD overlap.
Anti-IgE treatment (omalizumab [Xolair]) can be used in allergic asthma.
Anti-IL5 treatment (mepolizumab [Nucala], reslizumab [Cinqair], and benralizumab [Fasenra]) can be used in eosinophilic asthma.
Tezepelumab (Tezspire) is a biologic that treats severe asthma, like allergic asthma or eosinophilic asthma.
Anti IL-4 receptor antagonist (dupilumab, Dupixent) is approved for moderate to severe eosinophilic asthma. It is also approved for atopic dermatitis and nasal polyposis.
Chromones (cromolyn [Intal, Opticrom, Gastrocrom], nedocromil [Alocril]) stabilize mast cells (allergic cells) but are rarely used in clinical practice.
Theophylline (Respbid, Slo-Bid, Theo-24) also helps with bronchodilation (opening the airways) but is rarely used in clinical practice due to an unfavorable side-effect profile.
Systemic steroids (prednisone [Deltasone, Liquid Pred], prednisolone [Flo-Pred, Pediapred, Orapred, Orapred ODT], methylprednisolone [Medrol, Depo-Medrol, Solu-Medrol], dexamethasone [DexPak]) are potent anti-inflammatory agents that are routinely used to treat asthma exacerbations but pose numerous unwanted side effects if used repeatedly or chronically.
Numerous additional monoclonal antibodies are also currently being studied and will likely be available within the next couple of years.
Immunotherapy or allergy shots have been shown to decrease medication reliance in allergic asthma.
There are no home remedies that have proven benefit for asthma.

There is often concern about the potential long-term side effects of inhaled corticosteroids. Numerous studies have repeatedly shown that even long-term use of inhaled corticosteroids has very few if any sustained, clinically significant side effects, including changes in bone health, growth, or weight. However, the goal always remains to treat all individuals with the least amount of medication that is effective. Patients with asthma should be routinely reassessed for any appropriate changes to their medical regimen.

Asthma medications can be administered via inhalers either with or without a spacer or nebulized solution. It is important to note that if an individual has proper technique with an inhaler, the amount of medication deposited in the lungs is no different than that when using a nebulized solution. When prescribing asthma medications, it is essential to provide the appropriate teaching on proper delivery technique.

Smoking cessation and/or minimizing exposure to secondhand smoke are critical when treating asthma. Treating concurrent conditions such as allergic rhinitis and gastroesophageal reflux disease (GERD) may also improve asthma control. Vaccinations such as the annual influenza vaccination and pneumonia vaccination are also indicated.

Although the vast majority of individuals with asthma are treated as outpatients, treatment of severe exacerbations can require management in the emergency department or hospital. These individuals typically require the use of supplemental oxygen, early administration of systemic steroids, and frequent or even continuous administration of bronchodilators via a nebulized solution. Individuals at high risk for poor asthma outcomes are referred to a specialist (pulmonologist or allergist). The following factors should prompt consideration or referral:

History of ICU admission or multiple hospitalizations for asthma
History of multiple visits to the emergency department for asthma
History of frequent or daily use of systemic steroids for asthma
Ongoing symptoms despite the use of appropriate medications
Significant allergies contributing to poorly controlled asthma

What should someone do when experiencing an asthma attack?

Patients experiencing acute asthma symptoms should first use their rescue inhaler (albuterol). If asthma symptoms are worsening and use of albuterol is increasing, then asthma patients should have a medical evaluation. A course of oral steroids may be indicated and an adjustment in asthma maintenance therapy may be needed. If symptoms are rapidly progressive, asthma patients should seek emergency medical care.

What is an asthma action plan?

Patient education is a critical component in the successful management of asthma. An asthma action plan provides an individual with specific directions for daily asthma management and for adjusting medications in response to increasing symptoms or decreasing lung function.

What is the prognosis for asthma?

The prognosis for asthma is generally favorable. Children experience complete remission more often than adults. Although adults with asthma experience a greater rate of loss in their lung function as compared to age-controlled counterparts, this decline is usually not as severe as seen in other conditions, such as chronic obstructive pulmonary disease (COPD) or emphysema. Asthma in the absence of other comorbidities does not appear to shorten life expectancy. Risk factors for poor prognosis from asthma include

a history of hospitalizations, especially ICU admissions or intubation,
frequent reliance on systemic steroids,
significant medical comorbidities.

The airway narrowing in asthma may become fixed over time and can resemble COPD or emphysema. The other main complication of asthma is due to side effects from oral steroid use, which can include bone loss (osteoporosis), weight gain, and glucose intolerance.

Is it possible to prevent asthma?

With the increasing prevalence of asthma, numerous studies have looked for risk factors and ways to potentially prevent asthma. It has been shown that individuals living on farms are protected against wheezing, asthma, and even environmental allergies. The role of air pollution has been questioned in both the increased incidence of asthma and in regards to asthma exacerbations.

Climate change is also being studied as a factor in the increased incidence of asthma. Maternal smoking during pregnancy is a risk factor for asthma and poor outcomes. Tobacco smoke is also a significant risk factor for the development and progression of asthma. Treatment of environmental allergies with allergen immunotherapy, or allergy shots, has been shown to decrease a child’s risk of developing asthma. The development of asthma is ultimately a complex process influenced by many environmental and genetic factors, and currently there is no proven way to decrease an individual’s risk of developing asthma.

How Eosinophilic Asthma Differs From Other Asthma

When you have asthma, the airways in your lungs get narrow and swollen. They also make too much mucus. This sets off spasms in the tubes that let air in and out of your lungs (bronchial tubes). The spasms make it hard to breathe. You may also wheeze and cough. Its an ongoing, lifelong condition.

There are several different types of asthma. Each type has different triggers. These can be things such as exercising too hard or stuff in the air like smoke or pollen.

One type is a serious kind called eosinophilic asthma. Its harder to control with typical medications. Science links it to higher levels of white blood cells called eosinophils. These cells are part of your immune system. They help to kill things that dont belong in your body such as harmful bacteria. They also control inflammation.

Researchers have found that the more eosinophils in your blood, the more likely you are to have a serious asthma attack. But they arent sure what causes their numbers to go up. They have learned that eosinophilic asthma is different from other forms of the condition in a few ways:

Who It Impacts

Asthma often starts when youre a child, but the eosinophilic type most often appears in adults around middle age.

Even though this kind of asthma does happen in children and older adults, its more likely to first come on when youre between the ages of 35 and 50. Its not clear how many people it affects. But researchers think that less than 10% of people with asthma have a type as serious as eosinophilic asthma. Theyve also found that men and women get this type in equal numbers.

Triggers and Symptoms

Many times, an allergy to things like pollen or pet dander can trigger asthma symptoms. But people with eosinophilic asthma dont tend to have these allergies. What sets this type apart from other forms of the condition is a higher number of eosinophils in your blood, lung tissue, and coughed-up mucus (sputum).

Symptoms like wheezing, coughing, and shortness of breath happen in all types of asthma. But this kind affects your entire respiratory system. This means that youll likely get a lot of sinus infections. You may also get nasal polyps, noncancerous growths in the nasal passages or sinuses. You may also notice that the lining in your nose (mucous membrane) gets swollen and irritated.

Your symptoms may not look and feel like those of what you think of as typical asthma. They could seem more like chronic pulmonary obstructive disorder (COPD). This is a lung disease that causes long-term breathing problems and poor airflow. Sometimes doctors diagnose eosinophilic asthma as COPD by mistake.

Diagnosis

To figure out if you have asthma, your doctor will give you a physical exam. Theyll ask you about your symptoms and other health problems. You may also have to take lung function (pulmonary) tests. These will tell you how much air you can breathe out and how quickly you can do it.

To diagnose eosinophilic asthma, you may need some extra tests to look for eosinophils:

Blood test. A doctor or nurse will draw your blood to measure the number of eosinophils in it.
Sputum sample. Youll cough up a sample of mucus. Your doctor will then examine it under a microscope.
Bronchial biopsy. This test is less common. Your doctor will put a tool called a bronchoscope into your nose or mouth. Theyll use it to get several small tissue samples from your lungs (biopsy). Theyll analyze these for eosinophils. Youll need to drugs to stop pain (anesthesia). You may have to stay in the hospital.

Treatment

There are two goals for treatment of this type of asthma: control your breathing and reduce eosinophils. You may feel symptom relief from typical asthma treatments. These include drugs that stop inflammation (corticosteroids) and quick-relief inhalers (bronchodilators).

But these medications dont always work for people with eosinophilic asthma. Your doctor could also give you a medicine called a biologic. It targets eosinophils and makes your body less able to make them. Youll take it along with other asthma drugs.

Its important to diagnose and treat this condition early so you can stop lasting damage to your lungs, such as lung tissue scarring and thickened airway walls. See your doctor once a year to go over your treatment plan and make sure its still right for you.

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