Dark underarm skin? (photo)

I would recommend prepping the skin with Luminase and Exfolase creams followed by fractional laser. Best, Dr. Karamanoukian#Realself100 Surgeon

Chronic moisture in the thighs and underarms can result in hyperpigmentation.
This is called post-inflammatory hyperpigmentation (PIH). 
I recommend Melarase AM and Melarase PM creams from Kare Skin as well as a broad spectrum sunblock like Spectrase. Bothe are from Kare Skin. Scler-x post inflammatory hyperigmentation relief complex is a great supplement to take as well. See link below. 

Hi,Do you have similar darkening on the neck? If yes, you should check with your doctor for a diagnosis of a condition called Acanthosis Nigricans, which may have a hormonal/ metabolic basis. In that case, results of any lightening treatment may only be short lived unless the underlying problem is attended to.Good luck!

Many
times this pigmentation you see is a result from trauma to the area, for
example shaving the area can cause this. In many cases you can improve the
pigmentation, I recommend a series of salicylic acid peels to improve the
darkness. You can also use prescription hydroquinone of 4% on a nightly basis
to speed the lightening process along. However, this may cause irritation if
you continue to cause trauma to the area you can inhibit the amount of
improvement you will get. Based on the picture my recommendation is to get
laser hair removal in the area to stop the trauma and stop causing the
pigmentation. The combination of those three things will give you the best
results. Consult with a Board Certified Dermatologist to see what would best
benefit you.