White stains on black pants after washing- what can I do?

First ALWAYS turn inside out, use just a few tablespoons of Woolight or the likes, on a delicate or short, but large load cycle & wash only w/ same colors! Try soaking overnight in a 1/4 cup water vinegar in your washing machine then run through. I see clothes as an investment & keep mine for many years & I am a Great-Grandmother!

My hubbies and oldest sons black sweatshirt material pants get this too! It always wipes right off of them. It may be from suds not.. getting rinsed out completely for some reason. My hubby has soap allergies and I use a different detergent for his clothes and give them an extra rinse, so It doesn't happen with his very often, but the heavier the load the more it shows up. I do not use powder detergent, always liquid, so I know it isn't from undissolved detergent. I really don't know what it is from. I have heard of others complaining about the same thing with newer washing machines. Mine is about two years old and is an HE top load.

Thank you so much! I will try your suggestions. I always turn them inside out, but like you I try to keep my clothes a long time. One question, do I soak the clothes in vinegar or the washing machine?

You can soak your clothes in vinegar and cold water overnight. When you first buy them to set the color in. And after you dye clothes. You can run your black and darker color clothes through two rinses it does help. And in cold weather try awarm wash because when it's really cold outside like now the cold water is almost ice. Lol !!!