There is a considerable overlap in the pathogenesis and clinical features between asthma and COPD, however, asthma and COPD may be distinguished by their respective cytokine profiles.There is a complex relationship between asthma and COPD. There are populations of patients with COPD and asthma that can be readily distinguished from one another based on their physiology, natural history, and/or disease pathogenesis. There are many patients who appear to have features of both disorders. The relationship between asthma and COPD has been speculated on and investigated what is called British hypothesis.