BackgroundSpecific inhalation challenge tests (SIC) are still the reference test for diagnosing sensitizer-induced occupational asthma (SIOA). The European Respiratory Society recommends the cessation of inhaled corticosteroids (ICS) 72h prior to SIC. ObjectiveTo assess the effect of an ongoing ICS treatment during SIC on the maximum fall in FEV1, change in methacholine PC20 as well as sputum eosinophil counts after exposure to the suspected agent. MethodsWe performed a retrospective analysis using a database of cases referred to our center for suspected SIOA from 1999 to 2022. The results of the SIC were compared between subjects treated with ICS during SIC and steroid-naïve subjects. ResultsSix-hundred and seventy-one individuals underwent SIC in the laboratory. Three hundred and eighteen were treated with ICS, whereas 353 were steroid naïve. The proportion of subjects with a positive SIC was greater among ICS treated subjects (39. 6%) compared to steroid-naïve subjects (27.5%, p<0.001). A treatment with ICS did not influence the outcome of the SIC. There was no difference in the change in PC20 or percentage of sputum eosinophils after SIC between steroid-treated and steroid-naïve subjects. ConclusionAn ongoing ICS treatment during a SIC did not affect the occurrence of an asthmatic reaction, the change in airway responsiveness or eosinophilic inflammation after exposure to the suspected agent in subjects who have been treated with ICS for a long period of time.