Change your hair-removal method: Stop using hair dissolving/removal agents and depilatory creams and you’ll notice your dark armpits getting lighter. These products contain strong acids and other substances to remove hair, and darken the skin beneath.
Shave less: Shaving may also cause your armpits to darken, so shaving less frequently may help lighten them. Shaving only removes the top layer of skin along with the hair, the newly exposed layer can darken instantly when exposed to sweat. Try waxing underarms instead. It’s best to have your underarms waxed by a professional, as your skin is very sensitive in that area and can burn or bleed.
Loosen up: Tight blouses brush against armpit skin, and the friction can cause underarms to darken. Wear loose, breathable clothes instead.
Wash your underarms regularly: Poor hygiene can cause dirt and oil to accumulate in your armpits, which makes underarms dark. Wash well with soap, and rinse with warm water.
Raid the kitchen: Stir a paste of white vinegar and baking soda and apply to your underarms twice a day. Baking soda, a natural cleanser, combined with vinegar, a natural stain remover, can help whiten dark underarms.