This soap, in addition to being perfect for sensitive skin, is also a very good natural clothing whitener. You have several options for using it.
The first is to make your own homemade laundry detergent using Marseille soap. In this case, wash your laundry in the machine as you usually do and use your homemade detergent based on Marseille soap.
Otherwise, you can also pre-soap your white clothes with Marseille soap, let it sit for a few hours then put it in the machine with the rest of your clothes.