How do I whiten my dark armpits?

Bleach?

My wife said exfoliate. :)

I had the same problem when I was younger... Be sure to wash really well with a good soap. Don't go cheap on deoderant either I use dove it has moisturizers that keep you from drying out and from sweating so much. My doc also told me to be sure and where clothes that are able to bearth in the summer because it is caused by your clothes trapping sweat which can stain your underarms. Hope I could be of help

There are many factors that causes dark under arms. Under arms tend to get dark under from sweating, ingrown hairs or genetics. Try using an exfoliant, such as a mild scrub to help remove dead skin cells from the skin and help new skin cells come in. You can also use skin lightening creams containing kojic acid or hydroquinone to fade the dark discoloration.