Armpit stains are often not what they appear to be. Sometimes, the stains are actually from sweat. However, what looks like an embarrassing sweat stain may, in fact, be from your antiperspirant or deodorant. Chemicals from your deodorant can react with your skin's natural bacteria, resulting in yellow or brown discolouration in the armpit area of your shirts. Before you end up with a whole wardrobe of stained shirts, try a few simple tricks to nip this problem in the bud.
Apply just a thin layer of your antiperspirant deodorant under each arm, and wait until it dries before getting dressed -- don't overdo it. Putting your shirt on before it's dry will cause more transfer from your skin to your clothing, resulting in dark "pit" stains.
Switch antiperspirant deodorants if you're certain the stains you're dealing with are from sweat. If you've used the same brand for years, it might be time to try something new. Since the chemical make-up of each product is slightly different, you will likely see better results from trying a new brand. Many manufacturers also offer prescription-strength products without actually needing a prescription.
Wash your underarms twice daily with antibacterial soap and warm water. This will remove any sweat residue and keep your armpits fresh and clean. Be sure to apply more antiperspirant deodorant every time you wash your armpits, and wait until it's dry before getting dressed.
Try using baby powder on days when you foresee a whole lot of sweating going on. Sprinkle a small amount of powder in your hand and apply it to each armpit. The powder will absorb sweat and odour as well as protect your clothes from stains.
To treat existing armpit stains, make a paste of baking soda and water. Apply the paste to the stains, let it sit for several hours, and wash as usual. Don't put stained shirts in the dryer as the heat will set the stain.