Since moving I have started to get very large, stiff, slightly waxy or oily patches on the back of my t shirts after I wash them, exactly where my back leans against my chair. I think they're just sweat and soap and calcium buildup, but they're nearly impossible to get out completely. I've tried soaking in boiling water, soaking in vinegar, etc etc but nothing seems to quickly and completely get rid of them or prevent it from happening. They stay even after several washes or come back over time when I do manage to get rid of them. Normal cheap cotton-poly blend tees, being worn normally, washed on normal in HE washing machines with the recommended amount of liquid soap. Usually on warm or cold. I am hesitant to do hot very often because of the risk of damaging my clothes. This problem does not occur with my other clothes or my sheets, even when I sweat a lot. It's just specifically my T shirts for some reason?? Does anyone know a permanent solution to these kinds of stains?