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COPD is a serious, progressive condition that limits airflow in the lungs.

COPD is characterised by airflow limitation that is not fully reversible with the use of medication. People with COPD may also have a persistent cough with sputum due to excessive mucus production in the airways (known as chronic bronchitis) or evidence of lung tissue destruction, enlargement of the air sacs and further impaired lung function (known as emphysema). The terms COPD, emphysema and chronic bronchitis are often used interchangeably. 

COPD may be associated with other chronic conditions such as asthma, respiratory cancers, diabetes and diseases of the heart and blood vessels due to shared risk factors and the effect of COPD on other parts of the body. The main cause of COPD is active smoking or exposure to smoking, however other causes may be involved, such as [1]:

  • smoke from burning fuels of plant or animal origin
  • outdoor air pollution
  • fumes and dust in the workplace
  • childhood respiratory infections
  • chronic asthma.

It can be difficult to distinguish COPD from asthma because the symptoms of both conditions can be similar.

Although the current definitions of asthma [2] and COPD [3] overlap, there are some important features that distinguish typical COPD from typical asthma. For example, people with COPD continue to lose lung function despite taking medication, which is not a common feature of asthma.

There is increasing recognition of asthma-COPD overlap (also called asthma-COPD overlap syndrome, or ACOS), which affects around 15–20% of people with either diagnosis [4]. It is important to acknowledge this condition, which may have several different causes, as these patients have worse health outcomes than those with either condition alone, and it is not yet clear how to effectively treat it [5].  


  1. Salvi SS & Barnes PJ 2009. Chronic obstructive pulmonary disease in non-smokers. Lancet 374:733–43.
  2. Global Initiative for Asthma (GINA) 2015. Global Strategy for Asthma Management and Prevention 2015 (PDF)
  3. Global Initiative for Chronic Obstructive Lung Disease (GOLD) 2015. The Global Strategy for the Diagnosis, Management and Prevention of COPD 2015.
  4. Bateman ED, Reddel HK, van Zyl-Smit RN, Agusti A. The asthma-COPD overlap syndrome: towards a revised taxonomy of chronic airways diseases? Lancet Respir Med 2015; 3:719–28.
  5. Reddel HK. Treatment of overlapping asthma-chronic obstructive pulmonary disease: Can guidelines contribute in an evidence-free zone? J Allergy Clin Immunol 2015; 136:546–52.