Causes - Asthma
The exact cause of asthma is unknown, and the causes may vary from person to person. However, asthma is often the result of a strong response of the immune system to an allergen in the environment. For example, exposure to an allergen in the environment, such as ragweed, may make your airways react strongly. Other people exposed to the same allergen may not react at all, or their response may be different. The reason one person reacts to an exposure while others do not is not completely understood, though it may be partially explained by genes.
Asthma symptoms occur when the airways of the lungs narrow, which makes it more difficult to breathe. This narrowing is usually caused by, which makes the airways swell and may cause the cells of the airway to make excess mucus. Bronchospasm, or tightening of the muscles around the airways, also makes the airways narrow and results in trouble breathing.
Over time, if asthma remains active, the airway walls can become thicker. The image below shows how airways narrow during asthma.
See How the Lungs Work to learn more about airways.
The immune system, and its role in asthma, is complex.
Scientists have identified more than 100 types of immune cells and molecular pathways in the immune system that may play a role in causing asthma. Some of these play a role in inflammation. Studying these immune cells and pathways and the role they play can help researchers understand how to better manage asthma.
Genes seem to play a role in making some people more susceptible to asthma. For example, some genes are involved in how your immune system responds to allergens. These genes can cause a stronger reaction in your airways when certain substances in the air end up there. The genes involved may be different in different people.
Environmental exposures that may lead to asthma include airborne allergens and virus infections in infancy or early childhood when the immune system is developing.
- Risk Factors will discuss medical conditions, environmental situations, and other factors that can increase a person’s chance of developing asthma or triggering an asthma attack.
Risk Factors - Asthma
Asthma affects people of all ages, but it often starts during childhood. Sometimes asthma develops in adults, particularly women. This type of asthma is called adult-onset or late-onset asthma.
You may have an increased risk of asthma because of your environment or occupation, your family history or genes, other medical conditions, your race or ethnicity, or your sex.
Environment or occupation
Environmental exposures, including those at work, may increase the risk of developing asthma or making asthma symptoms worse.
- Exposure to cigarette smoke during pregnancy or in a child’s first few years increases the risk of the child developing asthma symptoms early in life. This exposure also may affect lung growth and development.
- Exposure to different in the environment, especially early in life, can affect the development of the immune system. These effects on the immune system may either increase or protect against the risk of developing asthma.
- Exposures that occur in the workplace, such as chemical irritants or industrial dusts, may also be associated with an increased risk of developing asthma in susceptible people. This type of asthma is called occupational asthma. It may develop over a period of years, and it often lasts even after you are no longer exposed.
- Poor air quality from pollution or allergens may worsen asthma. Pollutants include gases from heaters or vehicles. Allergens in the air include pollen, dust, or other air particles.
How does exposure to different microbes affect your risk of developing asthma?
Different types of microbes live throughout the environment and within each person’s body. The microbes may differ depending on the environment, such as where you live. Researchers found that being exposed to certain types of microbes or higher amounts of certain microbes during childhood can affect how your immune system develops. This in turn can determine whether you have allergic reactions later in life. For example, people who lived on farms as children were exposed to more types of microbes, and research suggests that this may have helped prevent asthma later in life. Learn more about our research that explores whether microbes might be involved in asthma related to dust-mite allergies.
Family history and genes
Genes and family history increase your risk of developing asthma.
- Having a parent who has asthma, especially if the mother has asthma, increases the risk that a child will develop asthma.
- The genes you may play a role in the development of asthma because they affect how the immune system develops. More than one gene is likely involved.
Other medical conditions
Asthma is often linked to other medical conditions, such as:
- Allergies. Asthma is usually a type of allergic reaction. People who have asthma often have other types of allergies. They may have food allergies or get a runny or stuffy nose from pollen. You may be at higher risk for developing asthma if you had allergic reactions in early childhood to substances in the air, such as pollen, dander, mold, or dust. The more things you are allergic to, the higher your risk of asthma.
- Respiratory infections and wheezing. Young children who often have respiratory infections caused by viruses are at highest risk of developing asthma symptoms early in life.
Race or ethnicity
African Americans and Puerto Ricans are at higher risk of asthma than people of other races or ethnicities. African American and Hispanic children are more likely to die from asthma-related causes than non-Hispanic white Americans.
Among children, more boys than girls have asthma. Among teens and adults, asthma is more common among women than men.
Screening and Prevention - Asthma
There is no routine screening for asthma, and there is no way to prevent asthma. Your doctor may recommend avoiding certain risk factors to help prevent asthma from getting worse or causing asthma attacks.
Signs, Symptoms, and Complications - Asthma
How oftenand of asthma occur may depend on how severe, or intense, the asthma is, and whether you are exposed to allergens. Some people have symptoms every day, while others have symptoms only a few days of the year. For some people, asthma may cause discomfort but does not interfere with daily activities. If you have more severe asthma, however, your asthma may limit what you are able to do.
When asthma is well controlled, it may not cause symptoms. When symptoms worsen, it is called an asthma attack, exacerbation, or flare-up. Over time, uncontrolled asthma can damage the lungs.
Signs and symptoms
Signs and symptoms of asthma may include:
- Chest tightness
- Coughing, especially at night or early morning
- Shortness of breath
- Wheezing, which causes a whistling sound when you exhale
Asthma attacks are episodes that occur when symptoms get much worse. Asthma attacks can happen suddenly and may be life-threatening. People who have severe asthma experience asthma attacks more often.
While other conditions can cause the same symptoms as asthma, the pattern of symptoms in people who have asthma usually has some of the following characteristics:
- They come and go over time, or within the same day.
- They start or get worse with viral infections, such as a cold.
- They are triggered by exercise, allergies, cold air, or from laughing or crying.
- They are worse at night or in the morning.
Diagnosis - Asthma
Your doctor may diagnose asthma based on your medical history, a physical exam, and results from diagnostic tests. Your history of asthma symptoms will help your doctor determine if you have mild, moderate, or severe asthma. The level of severity is used to determine the treatment you will receive.
Before diagnosing you with asthma, your doctor will rule out other medical reasons or conditions that could also cause similar signs and symptoms. You may need to see an asthma specialist, called a pulmonologist, or an allergy specialist, called an allergist.
Your doctor may ask about any known allergies and the pattern of your symptoms. This includes how often symptoms occur, what seems to trigger your symptoms, when or where symptoms occur, and if your symptoms wake you up at night.
During the physical exam, your doctor may:
- Listen to your breathing and look for signs of asthma such as wheezing, a runny nose, or swollen nasal passages
- Look for allergic skin conditions, such as eczema
Several tests may be done to help determine if asthma is likely to be the cause of symptoms. These tests include:
- Pulmonary function tests such as spirometry, which involves breathing in and out through a tube connected to a computer. This measures how much and how fast the air moves when you breathe in and out with maximum effort.
- Spirometry with bronchodilator (BD) test to measure how much and how fast air moves in and out both before and after you take an inhaled medicine to relax the muscles in your airway.
- Bronchoprovocation tests to measure how your airways react to specific exposures. During this test, you inhale different concentrations of allergens or medicines that may tighten the muscles in your airways. Spirometry can also be done before and after the test.
- Peak expiratory flow (PEF) to measure how fast you can blow air out using maximum effort. This test can be done during spirometry or by breathing into a separate device, such as a tube.
Diagnosing asthma in children under age 6
It can be hard to tell whether a child under 6 years old has asthma or another respiratory condition because they cannot perform a pulmonary function test such as spirometry. After checking a child’s history and symptoms, the doctor may try asthma medicines for a few months to see how well a child responds. About 40 percent of children who wheeze when they get colds or respiratory infections are eventually diagnosed with asthma.
If you have a history of allergies, your doctor may test to find out which allergens in the environment, such as pet dander or pollen, affect you. This can be a skin test or a blood test.
Tests for other medical conditions
Your doctor may want to test for other conditions if your symptoms include:
- A cough without other breathing issues
- Chest pain
- Coughing up mucus often
- Difficult and noisy breathing during exercise
- Shortness of breath with dizziness, light-headedness, or tingling in your hands or feet
Tests your doctor may use to rule out other medical conditions include:
- Chest X-ray to rule out lung infections, such as tuberculosis, or a foreign substance, such as an object that was inhaled by accident.
- Electrocardiogram (EKG) to rule out heart failure or arrhythmia while in emergency care.
- Laryngoscopy to rule out vocal cord problems. The doctor can use this test to look at your upper airways and the vocal cords.
- Sleep studies to rule out sleep apnea.
- Tests that look at your esophagus and upper digestive system to rule out gastroesophageal reflux disease (GERD). These tests may include endoscopy, in which a small camera is placed in the esophagus, or an X-ray of the digestive system. Tests may also measure the acid in your esophagus or measure how food or other substances move through the esophagus. Some people have both GERD and asthma.
Treatment - Asthma
If you are like most people who have asthma, treatment can manage your symptoms, allow you to resume normal activities, and prevent asthma attacks. Treatment usually depends on your age, asthma severity, and your response to a given treatment option. Your doctor may adjust your treatment until asthma symptoms are controlled.
Most people who have asthma are treated with daily medicine, called long-term control medicines, along with inhalers containing medicine for short-term relief during an asthma attack or when symptoms worsen. An inhaler allows the medicine to go into the mouth and airways.
Your doctor may prescribe control medicines to take daily to help prevent symptoms by reducing airway inflammation and preventing narrowing of the airways. Return to Causes to review what causes asthma symptoms.
Control medicines include the following:
- Corticosteroids to reduce the body’s inflammatory response. Your doctor may prescribe inhaled corticosteroids that you will need to take each day. If your symptoms get worse, your doctor may increase the dose of the inhaled corticosteroids to prevent severe asthma attacks or even give corticosteroids by mouth for short periods. Common side effects from inhaled corticosteroids include a hoarse voice or a mouth infection called thrush. A spacer or holding chamber on your inhaler can help avoid these side effects. Using high-dose inhaled corticosteroids more often or for longer periods may affect growth in young children. Oral corticosteroids also have more side effects than inhaled corticosteroids because more of the medicine goes outside the lungs.
- Biologics, such as omalizumab, mepolizumab, resulizumab, and benralizumab, to target specific parts of the body’s response to allergens. Biologics are antibodies used in people who have severe asthma. These medicines are given by injection, either below the skin or in a vein, every few weeks.
- Leukotriene modifiers to reduce the effects of leukotrienes, which are released in the body as part of the response to allergens. Leukotrienes cause the airway muscles to tighten. These medicines block this response, allowing the airways to open, and reduce inflammation. You take these pills by mouth, alone or with corticosteroids, depending on what your doctor prescribes.
- Mast cell stabilizers such as cromolyn, to help prevent airway inflammation caused by exposure to allergens or other triggers. These medicines stop certain immune cells from releasing the signals that cause inflammation.
- Inhaled long-acting beta2-agonists (LABAs) keep the airways open by preventing narrowing of the airways. LABAs may be added to your inhaled corticosteroids to reduce narrowing and inflammation.
Short-term relief medicines
Short-term relief medicines, also called quick-relief medicines, help prevent symptoms or relieve symptoms during an asthma attack. They may be the only medicine needed for mild asthma or asthma that only happens with physical activity.
Your doctor will prescribe a quick-relief inhaler for you or your child to carry at all times. Learn how to use your asthma inhaler correctly.
Types of short-term relief medicines include:
- Inhaled short-acting beta2-agonists (SABAs) to quickly relax tight muscles around your airways. This allows the airways to open up so air can flow through them. Side effects can include tremors and rapid heartbeat. SABAs are usually the only medicine used to treat wheezing in children under 5 years old. If symptoms and medical history suggest asthma, doctors may treat it with inhaled corticosteroids for a trial period to see if they help. If symptoms do not improve, corticosteroids will be stopped to avoid side effects.
- Oral and intravenous (IV) corticosteroids to reduce inflammation caused by severe asthma symptoms.
- Short-acting anticholinergics to help open the airways quickly. This medicine may be less effective than SABAs, but it is an option for people who may have side effects from SABAs.
If you have a severe asthma attack and need emergency care, you may be treated with medicines, such as those listed above, given with a nebulizer or IV. You may also receive oxygen therapy or breathing assistance, either through a tube inserted in the airway or through noninvasive ventilation, which uses a mask with forced air that covers the face to support breathing.
Your doctor may recommend a procedure called bronchial thermoplasty if you have severe asthma and other treatments are not working. In this procedure, your doctor will enter the airways through the mouth with a bronchoscope. This helps your doctor see inside the airways. Your doctor then will apply heat to the muscles along the airways to make them thinner and help prevent constriction.
- Research for Your Health will discuss how we are using current research and advancing research to treat people who have asthma.
- Participate in NHLBI Clinical Trials will explain our open and enrolling clinical studies that are investigating treatments for asthma.
- Living With will discuss what your doctor may recommend including lifelong lifestyle changes and medical care to prevent your asthma from getting worse or having an asthma attack.
Living With - Asthma
If you or your child has been diagnosed with asthma, work with your doctor to learn how manage it yourself. Because asthma symptoms may be different at different times, it is important to know which medicines to use to prevent and relieve symptoms. You can work with your doctor to develop a treatment plan, called an asthma action plan. Follow-up care will help to make sure your or your child’s asthma is well-controlled. Staying healthy also includes avoiding asthma triggers and maintaining a healthy lifestyle.
Follow your asthma action plan
Work with your doctor to create an asthma action plan that works for you. An asthma action plan is a written treatment plan document that describes the following:
- How to identify allergens or irritants to avoid
- How to recognize and handle asthma attacks
- Which medicines to take and when to take them
- When to call your doctor or go to the emergency room
- Who to contact in case of an emergency
If your child has asthma, then all of your child’s caretakers and school staff should know about the asthma action plan. For a sample plan, see the National Heart, Lung, and Blood Institute’s (NHLBI’s) Asthma Action Plan.
Receive routine medical care
Regular checkups are important to help your doctor determine how well you are controlling your asthma and adjust treatment if needed. Your doctor will also do regular tests to see how well your lungs are working and how well air is flowing.
Your asthma is well-controlled if you have reached these markers:
- You can do all of your normal activities.
- You do not have symptoms more than twice a week.
- You do not have more than one asthma attack a year requiring corticosteroids by mouth.
- You do not take quick-relief medicines more than two days a week.
- You do not wake from sleep more than one or two times a month because of symptoms
Symptoms in young children who do not have their asthma controlled include, irritability, and mood changes.
Your doctor will also make sure you are using your inhaler correctly. There are different types of inhalers. Review the way you use your inhaler at every medical visit. Sometimes asthma may get worse because of incorrect inhaler use.
Medical care is also important for managing conditions that can make it harder to treat asthma, such as gastroesophageal reflux disease (GERD) or sinus infections. Work with your doctor to help keep them under control.
Your medicines or dosages may change over time, based on changes in your condition or in your life, such as:
- Age. Older adults may need different treatments because of other conditions they may have and medicines they take. Beta-blockers, pain relievers, and anti-inflammatory medicines can affect asthma.
- Pregnancy. Your asthma symptoms may change during pregnancy. You are also at increased risk of asthma attacks. Your doctor will continue to treat you with long-term medicines such as inhaled corticosteroids. Controlling your asthma is important to prevent complications such as preeclampsia, pre-term delivery, and low birth weight of the baby.
- Surgery. Asthma may increase your risk of complications during and after surgery. For instance, having a tube put into your throat may cause an asthma attack. Talk to your doctor and surgeon about how to prepare for surgery.
Return to Treatment to review possible treatment options for your asthma.
Monitor your asthma at home
Monitoring and managing your asthma at home is important for your health. Ask your doctor about asthma training or support groups. Education can help you understand your asthma, the purpose of your medicines, how to prevent symptoms, how to recognize asthma attacks early, and when to seek medical attention.
Your doctor may show you how to monitor your asthma using a peak flow meter. You can compare your numbers over time to make sure your asthma is controlled. A low number can help warn you of an asthma attack, even before you notice symptoms. Learn how to measure peak flow.
Keeping a diary may help if you find it hard to follow your asthma action plan or the plan is not working well. If you have any of the following experiences, record them in the diary and make an appointment to see your doctor. Bring the diary with you to your appointment.
- You are limiting normal activities and missing school or work.
- You have to use your quick-relief inhaler more than two days a week.
- Your asthma medicines do not seem to work well anymore.
- Your peak flow number is low or varies a lot from day to day.
- Your symptoms occur more often, are more severe, or cause you to lose sleep.
Adopt healthy lifestyle changes
Your doctor may recommend one or more of the following lifestyle changes to help keep asthma symptoms in check:
- Aiming for a healthy weight. Obesity can make asthma harder to manage. Talk to your doctor about programs that can help. Even a 5 to 10 percent weight loss can help symptoms.
- Being physically active. Even though exercise is an asthma trigger for some people, you should not avoid it. Physical activity is an important part of a healthy lifestyle. Talk with your doctor about what level of physical activity is right for you. Ask about medicines that can help you stay active.
- Heart-healthy eating. Eating more fruits and vegetables, and getting enough vitamin D, can provide important health benefits that may help you with asthma control.
- Managing stress. Learn breathing and relaxation techniques, which can help symptoms. Meet with a mental health professional if you have anxiety, depression, or panic attacks.
- Quiting smoking or avoiding secondhand smoke. Smoking tobacco and smoke from secondhand smoke make asthma harder to treat. Visit Smoking and Your Heart and NHLBI’s Your Guide to a Healthy Heart. These resources include basic information about how to quit smoking. For free help and support, you may call the National Cancer Institute’s Smoking Quitline at 1-877-44U-QUIT (1-877-448-7848).
Prevent worsening of asthma symptoms and attacks
Certain things can set off or worsen asthma symptoms. These are called asthma triggers. Once you know what these triggers are, you can take steps to control many of them.
A common trigger for asthma is exposure to allergens.
- If animal fur triggers asthma symptoms, keep pets with fur out of your home or bedrooms.
- Keep your house as dust-free and mold-free as possible.
- Remove yourself from what is triggering your symptoms in the workplace. If you have occupational asthma, even low levels of the substance to which you are sensitive can trigger symptoms.
- Try to limit time outdoors if allergen levels are high.
Other asthma triggers include:
- Emotional stress. Emotional stress, such as intense anger, crying, or laughing, can cause hyperventilation and airway narrowing, triggering an asthma attack.
- Influenza (flu). Get the flu vaccine each year to help prevent the flu, which can increase the risk of an asthma attack.
- Medicines. Some people who have severe asthma may be sensitive to medicines, such as aspirin, and may experience serious respiratory problems. Tell your doctor about all medicines you or your child currently take.
- Poor air quality or very cold air. Pollution or certain kinds of weather, such as thunderstorms, can affect air quality. Pollution can include indoor pollution caused by gases from inefficient cooking or heating devices that are not vented. Outdoor air pollution may be hard to avoid, but you can keep windows closed and avoid strenuous outdoor activity when air quality is low. For guidance, check the National Oceanic and Atmospheric Administration’s Air Quality Forecast Guidance.
- Tobacco smoke, including secondhand smoke.
Return to Risk Factors to review environments that can trigger asthma.
Prevent and treat complications over your lifetime
To help you prevent complications, your doctor may recommend the following:
- Keeping your medicine dose as low as possible to prevent long-term side effects. High doses over time can increase your risk of cataracts and osteoporosis. A cataract is the clouding of lens in your eye. Osteoporosis is a disorder that makes your bones weak and more likely to break.
- Monitoring your asthma and contacting your doctor if anything changes. When asthma is unmanaged, it can lead to potentially life-threatening asthma attacks. If you are pregnant, it can put the health of your baby at risk.
Learn the warning signs of serious complications and have a plan
Ask your doctor about when to call 9-1-1 for emergency care. It should be written in your asthma action plan.
Call your doctor in these cases:
- Your medicines do not relieve an asthma attack.
- Your peak flow number is low.
Improving health with current research
Learn about the following ways the NHLBI continues to translate current research into improved health for people who have asthma. Research on this topic is part of the NHLBI’s broader commitment to advancing lung disease and health disparities and inequities scientific discovery.
- Advancing the Understanding of Lung Development. The Molecular Atlas of Lung Development Program (LungMAP) is integrating many datasets to build a molecular map of the developing lung in both humans and mice. The program is helping advance lung research, in part through its Web-based data resource, called BREATH, that allows users to access LungMAP data and findings.
- Developing Guidelines for the Diagnosis and Management of Asthma. The Expert Panel Report (EPR) 3 Guidelines on Asthma was developed in 2007 by an expert panel through the National Asthma Education and Prevention Program (NAEPP) Coordinating Committee and NHLBI. The expert panel organized the report to focus on assessment and monitoring, patient education, control of factors contributing to asthma severity, and medicines. View the EPR-3 Summary Report.
- Expert Panel Report Working Group 4. The EPR-4 Working Group was established in 2018 to update the 2007 Expert Panel Report (EPR) 3 Guidelines on Asthma. The working group members will review the latest research to update the guidelines on treatments and management of asthma, including the role of immunotherapy, the effectiveness of indoor allergen reduction, and the use of fractional exhaled nitric oxide (FeNo).
- Future Research Directions in Asthma Workshop. The NHLBI convened a group of investigators for an Asthma Research Strategic Planning workshop in 2014 that focused on the use of types to classify disease, defining disease modification, asthma management, and implementation research. Visit Future Research Directions in Asthma: An NHLBI Working Group Report for more information.
- Providing Resources for Research. The Lung Tissue Research Consortium (LTRC) provides human lung tissues to qualified investigators for use in their research. The program enrolls patients who are planning to have lung surgery, collects blood and other clinical data from these donors, and stores donated tissue that otherwise would be discarded after the lung surgery. The LTRC provides tissue samples and data at no cost to approved investigators.
- Supporting New Approaches to Asthma Treatments. AsthmaNet is a nationwide clinical research network that developed and conducted studies to explore new approaches for treating asthma from childhood through adulthood. AsthmaNet studies were conducted in 13 states.
- Supporting Research Collaboration. The Pulmonary Trials Cooperative brings together patients, researchers, and healthcare professionals from more than 50 institutions, with a common goal of developing new treatments and testing current clinical care practices.
- The National Asthma Education and Prevention Program (NAEPP). The NAEPP raises awareness about asthma as a major public health problem. Working with medical associations, voluntary health organizations, and community programs, NAEPP helps to educate patients, healthcare professionals, and the public about asthma.
Advancing research for improved health
In support of our mission, we are committed to advancing asthma research in part through the following ways.
- We perform research. Our Division of Intramural Research and its Pulmonary Branch perform research on asthma.
- We fund research. The research we fund today will help improve our future health. Our Division of Lung Diseases and its Airway Biology and Disease Branch oversee much of the research on asthma we fund, helping us to understand asthma. Our Center for Translation Research and Implementation Science and its Health Inequities and Global Health Branch provide guidance to domestic and global implementation research on heart, lung, and blood, and sleep health disparities, including asthma. Search the NIH RePORTer to learn about research NHLBI is funding on asthma.
- We stimulate high-impact research. Our Trans-Omics for Precision Medicine (TOPMed) Program includes participants who have asthma, which may help us understand how genes contribute to differences in disease severity and how patients respond to treatment. The NHLBI Strategic Vision highlights ways we may support research over the next decade.
Learn about exciting research areas that the NHLBI is exploring about asthma.
- A hormone in bone tissue may be important in asthma symptoms. A study supported by the NHLBI will look at the importance of this hormone in causing the constriction of airways in mice that have asthma, to help future treatments.
- Addressing asthma disparities among children. We support studies to evaluate asthma programs that provide comprehensive care for children at high risk of poor asthma outcomes.
- Evaluating how the body’s microbes may affect allergies and asthma. We know that the different bacteria in a person’s body can affect immunity. We are supporting studies to figure out whether different bacteria play a role in development of dust mite allergy-related asthma.
- Gaining a better understanding of chronic inflammation. Previous studies have shown that a certain type of cell in the airways is involved in asthma inflammation. The NHBLI is supporting the continuation of this study to find specific targets to prevent asthma from worsening.
- Reducing asthma disparities. The goals of the Consortium on Asthma among African-Ancestry Populations in the Americas (CAAPA) aims to discover genes that increase asthma risk among people of African ancestry and to study genetic diversity in populations of African descent.
We lead or sponsor many studies on asthma. See if you or someone you know is eligible to participate in our.
Are you an adult who has asthma and allergies and is willing to undergo brain imaging tests?
Does your child have asthma and an African American or Puerto Rican family background?
Are you a young African American adult who has asthma and lives in or near Detroit?
Are you an adult who has asthma and wants to help researchers better understand it?
Does your child have asthma and live in or near the Bronx?
Do you or your child have a lung disease?
Are you an adult who has asthma and wants to help with understanding airway biology?
Does your teenager have asthma and want to learn how to better control it?
Are you an adult who has asthma and insomnia?
Do you have depression and act as caregiver for a child who has asthma?
Does your child have asthma and vitamin D deficiency?
After reading our Asthma Health Topic, you may be interested in additional information found in the following resources.