The specific problem we had was that dust and fluff was coming from the AC vents. This was evident on floors and surfaces. The more urgent issue was how this substance affected our health to the extent we had to leave after a week of a 4 week stay due to the risks to our health. Today is the 4th day since we left the flat and we are still suffering from the affects. On a positive note, Airbnb were extremely helpful in resolving our issue very fairly and speedily with excellent communication.