An inspection device is provided to monitor hygienic conditions of a space unit for a vehicle. The vehicle includes, but is not limited to, an inspection device, the use of an inspection device, and a method to assure hygienic conditions in a vehicle. In order to optimize assuring hygienic conditions in interior spaces on board a vehicle an inspection device is provided that includes, but is not limited to, an optical detection device. The optical detection device generates electromagnetic radiation to irradiate a surface to be cleaned, and renders visible soiling that, in visible light, is invisible to the human eye. The optical detection device is permanently installable on an interior lining.