I had the same problem and I used to end up with an itchy red rash. I tried various powders and the Persil non-biological tablets were the best for my sensitive skin. These tablets are put in the drum not in the tray. Only one tablet per wash. I go along with what the others have said. Make sure the tray is clean including any dried on powder. Change or clean the filter often and depending on how often the machine is used, put it through the hottest wash you can manage with the drum empty. That is what works for me
Alan