When freshly washed laundry emerges with a powdery clothing stains, the cause is one of two things:
Regardless of the cause, you can remove and prevent them. Here's how to make powdery stains a thing of the past.
Set the wash water temperature to warm. Laundry detergent is designed to be activated by warmer water. This will help the detergent dissolve completely so that it is not redeposited back on your clothes.
Add an extra rinse cycle to each wash load. This can help ensure any powdery residue coming from your laundry detergent is fully washed away in the rinse cycle.
Often, placing the laundry detergent in on top of garments can be the sole cause of powdery residue. Add your detergent before you toss in the dirty clothes to prevent it from becoming stuck on clothes.
A more common culprit, however, is a packed washing machine. Too many clothes in a load doesn't allow the machine adequate space or water to get clothes fully clean and can result in laundry detergent remaining on the clothes after the cycle is complete.
Finally, if nothing else works, consider changing to a liquid laundry detergent.