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These lung diseases share some similarities, but they are separate conditions. ACOS is a recent term, and research into the causes and treatment is in its early stages. Recognizing ACOS as the co-occurrence of two separate diseases helps doctors tailor the treatment to make it specific to a person’s symptoms. This article examines the symptoms, causes, and treatment of ACOS and explains how doctors diagnose it. What is asthma COPD overlap syndrome Share on PinterestAir Rabbit/Getty ImagesDoctors diagnose ACOS when a person has symptoms of asthma and COPD. Both of these conditions make breathing difficult. However, as the American Lung Association (ALA) notes, they are two different lung diseases. ACOS is not a separate condition but an umbrella term that doctors use when both asthma and COPD are present. COPD itself is also an umbrella term for two chronic lung conditions: emphysema and chronic bronchitis. Symptoms The ALA identifies the following as symptoms of ACOS:problems with breathingexcessive amounts of mucusfatiguefrequent coughingfrequent shortness of breathwheezing The American College of Asthma, Allergy, & Immunology also cites a feeling of tightness in the chest and a low tolerance for physical activities, such as exercise. A small 2018 study involving 30 people, 20 of whom had ACOS, found that shortness of breath was the most frequent symptom and the one that caused the most discomfort. It also found that people with ACOS were more likely to experience an exacerbation of symptoms than those with COPD but not asthma. These attacks can involve coughing more than usual, being sick, or being unable to breathe. A 2022 study also found that in comparison with people with COPD or asthma, those with ACOS are more likely to have:a lower quality of lifemore severe symptomsmore frequent flare-ups Diagnosis Clinical definitions of ACOS vary, but doctors usually refer to the following criteria:persistent airflow obstruction, which may or may not be reversiblehistory or symptoms of asthmahistory of smokingtwo positive responses to bronchodilator reversibility testshistory of rhinitis or allergies Doctors will begin testing with a pulmonary function test, known as spirometry. They may then use bronchodilator reversibility tests, in which they will give a person a bronchodilator to inhale and then measure how significantly this improves their breathing. A 2022 study looked at the effectiveness of bronchodilator testing when doctors performed it without spirometry. The results showed that it could increase the risk of ACOS misdiagnosis by up to almost 20%. A doctor will also take a detailed medical history and perform a physical examination. They may sometimes order imaging tests, such as an X-ray, CT scan, or MRI scan, to look at the lungs. As a 2021 study points out, the criteria for what defines ACOS are still under debate, and researchers continue to work on new methods of testing and diagnosis. The uncertainty around diagnosis means that it is difficult to be sure of the prevalence of ACOS. Studies show significant variations, with estimates ranging from just under 1 in 100 people to more than 1 in 10 people. However, a large-scale 2019 analysis of data for the Clinical Respiratory Journal states that it affects about 1% of the population in the United States. Causes and triggers As ACOS refers to the presence of both asthma and COPD, it is necessary to look at the causes and triggers of each of these in turn. Asthma causes and triggers Respiratory experts do not know exactly what causes asthma. However, there are some known risk factors, including:a family history of asthma or allergiessmoking tobaccobeing exposed to smoke when in the wombobesityliving in an area with poor air quality Common triggers that cause asthma flare-ups include dust mites, smoke, mold spores, pet dander, poor air quality, and strong smells. Stressful situations, viral and bacterial infections, weather changes, and physical exercise can also produce or worsen symptoms. COPD causes and triggers The World Health Organization (WHO) notes that COPD develops gradually over years, with the following factors increasing a person’s risk of developing the disease:exposure to tobacco smoke, harmful chemicals or fumes, or indoor air pollutionimpaired growth in the womb or premature birthfrequent respiratory infections or asthma in childhooda rare genetic condition called alpha-1 antitrypsin deficiency The primary triggers of COPD are viral and bacterial infections. Some people with COPD are more susceptible to these infections than others and are, as a result, likely to experience more frequent flare-ups. ACOS causes and triggers More recent studies have aimed to look at the potential causes of ACOS. A 2021 study has cited emerging evidence that certain risk factors may cause people with pre-existing respiratory problems to develop ACOS. These risk factors include childhood respiratory illness, smoking, and environmental factors, such as exposure to harmful fumes. Treatment As the ALA points out, treatment for ACOS is not straightforward, and no single medication can improve the symptoms of ACOS. However, certain drugs can help improve the symptoms. These include:Long-acting muscarinic receptor agonists: Doctors recommend these drugs for people with COPD, as they help stop the airways from tightening and producing excess mucus or phlegm. Studies have shown that they are effective in both asthma and COPD. Experts recommend using them as a first-line treatment for ACOS, with inhaled steroids as an add-on treatment.Low dose inhaled corticosteroids: These drugs treat inflammation in the airways. A 2022 study showed that although people with ACOS experienced more severe symptoms than people with asthma or COPD alone, they had a better response to inhaled corticosteroid treatment.Long-acting bronchodilators: These asthma medications keep the airways open for longer. Doctors will combine the medication with anti-inflammatory drugs.Biologics: Researchers are still investigating the potential role of biologics in ACOS treatment, but doctors may add this therapy to a person’s treatment regimen if their current medications are proving ineffective. More recently, studies have shown that a drug called roflumilast, which has anti-inflammatory properties, is effective in treating people with asthma, COPD, or ACOS. A doctor will also recommend making certain lifestyle adjustments. These include:stopping smoking, if applicablegetting vaccinations against respiratory illnesses such as influenza and pneumoniaengaging in regular physical activity to improve overall health In some cases, it may be necessary to refer a person with ACOS to a specialist. Outlook ACOS is a chronic disease, which means that there is no cure. People with ACOS tend to have a higher disease burden than people with asthma or COPD. This means that they are more vulnerable to infections and more likely to see their symptoms worsen over time. They are also more likely to have a lower quality of life. However, it is important to remember that the identification and treatment of ACOS are in their infancy. Clinicians and scientists are conducting new research and clinical trials to improve outcomes for people with ACOS. Summary Asthma COPD overlap syndrome is a term that doctors use when a person has both asthma and chronic obstructive pulmonary disease. The symptoms include shortness of breath, fatigue, and wheezing. Experts are still working to discover the causes, but they believe that childhood respiratory illnesses and smoking play a role. Doctors will create a tailored treatment plan for a person with ACOS, but they will typically recommend treatments for asthma and COPD. Last medically reviewed on July 28, 2022AsthmaCOPDPulmonary SystemRespiratory 19 sourcescollapsedMedical News Today has strict sourcing guidelines and draws only from peer-reviewed studies, academic research institutions, and medical journals and associations. We avoid using tertiary references. We link primary sources — including studies, scientific references, and statistics — within each article and also list them in the resources section at the bottom of our articles. You can learn more about how we ensure our content is accurate and current by reading our editorial policy.Annangi, S., et al. (2022). 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Epidemiology of asthma-chronic obstructive pulmonary disease overlap (ACO).https://www.sciencedirect.com/science/article/pii/S1323893018300066?via%3Dihub#sec3FEEDBACK:Medically reviewed by Nick Villalobos, MD — By Joanne Lewsley on July 28, 2022 Latest newsWhat sets 'SuperAgers' apart? Their unusually large neuronsOmega-3 may provide a brain boost for people in midlifeSeasonal affective disorder (SAD): How to beat it this fall and winterCDC: Monkeypox in the US 'unlikely to be eliminated in the near future'Why are more women prone to Alzheimer's? New clues arise Related CoverageAre asthma and COPD the same?Medically reviewed by Judith Marcin, M.D. Asthma and chronic obstructive pulmonary disease (COPD) are both conditions that affect the lungs. They can have similar symptoms, including breathing…READ MOREWhat causes asthma complications? Asthma is a chronic condition affecting the lungs that can lead to serious complications. 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