Underarm dark brown spots

I have this very black dark spot on my underams. Ever since I was a teen.  I really want to get rid of them now.  I am 25 yrs old and envy everyone who van raise their arms with no problems.  What can I use to get rid of them?  Please help me!

[Dr_Aparna]

Hi,
Hyperkeratosis is a thickening of the skin that occurs in women with brown skin. It is due to excessive accumulation of keratin in the outer layers of the skin. Thickening of the skin protects it against rubbing, pressure and irritation.
Hyper-pigmentation of the affected areas often accompanies this condition.Most treatments are aimed at softening the keratin and removing the thickened skin. This may be accomplished with topical creams that contain as the active ingredient salicylic acid, alpha-hydroxy acid (lactic or glycolic acid), urea, or tretinoin.
In brown skin, discoloration often accompanies the hyperkeratosis and skin lightening creams  like Hydroquinone 2-4% may be used.
ref:http://www.brownskin.net/hyperkeratosis.html