Most of the time, what people refer to as deodorants are actually antiperspirants that contain aluminum salts.
This active ingredient reduces sweat flow in the underarm areas by constricting the upper part of sweat glands. Antiperspirants also help to reduce bacteria that cause bad odor.
When it comes to stains, these can occur for a number of reasons. They are usually caused by a complex interaction of sebum, laundry detergent and aluminium salts. But, yellow stains can also form without an antiperspirant because skin lipids mixed with dirt particles can also stain clothes.