How can I remove the white deodorant marks out of a knit top?
For a light smear of deodorant that happened when you were putting on the top, try pretreating the stain before washing. Your pretreating method depends on the shirt.
For white, bleachable fabrics (100% cotton, 100% polyester, or a cotton/poly blend – note that you should never bleach wool, silk, mohair, leather, and spandex):
For colored washable fabrics (also white fabrics with spandex in them):
These are both good for breaking up the water repellent component of the deodorant, making it easier for the stain to come out in the regular wash cycle – liquid laundry detergent can also be used.
I also wanted to mention that you can keep underarm stains (usually a combination of deodorant, sweat and body soil concentrated in the arm pit area) from building up in the first place by pretreating the underarm area of your shirts every time you wash them, whether or not you see stains.