Asthma–COPD overlap (ACO) has recently been recognised as a separate phenotype of obstructive airway diseases and is included in several guidelines of asthma and COPD [1–5]. ACO patients have previously been shown to have lower diffusing capacity of the lung, higher blood neutrophil counts and higher interleukin-6 levels compared with asthma patients . In COPD, fixed airway obstruction is considered to develop in response to chronic exposure to noxious inhaled particles . In western countries, the most common cause of COPD is tobacco smoking, but occupational exposure to dusts and fumes has also been shown to increase the risk for developing COPD [7, 8]. However, the role of occupational exposures in the development of ACO is not known.