Hyperpigmentation, or darkness under the arms can be an embarrassing problem. In African Americans, the underarms can turn very dark, or black. Dark underarms can be caused by razor burn or the aluminum in some deodorants.
There are products on the market to lighten the armpits if this is your problem.
Here is a video of a young lady who used Xtreme Brite for 2 months. I think the product did a great job! But you Obviously must use the product consistently for best results.