Perspiration stains are almost a reason to toss your white shirts! Before you do, try crushing about 3 aspirins in a bowl. Add enough water to make a paste. Spread on the stains and let sit overnight. In the morning rinse with hot water and wash as usual. The salicylic acid in the aspirin will have loosened the oils and antiperspirant residue that cause the yellow color while lightening set-in stains and preventing new ones!