Some of the main causes of dark armpits are shaving, sweating, poor exposure to air of the armpits, the accumulation of dead skin cells, and the use of deodorants and antiperspirants that are alcohol-based.
Sodium bicarbonate scrub can help you get rid of dark armpits. Namely sodium bicarbonate will help you remove all the dead skin cells.
All you have to do is mix a little bit of baking soda and water, just enough to make a thick paste. Use this paste to rub your armpit. After that you need to wash and pat dry the area.
Repeat this procedure several times a week, before going to bed.