When you have a strong deodorant, your underarms would really darken. I don't know if plucking or shaving is a factor as well. Anyway, they say that when you use lemon before taking a bath would somehow lessen it. And have you tried the milk bath? It could be effective too.

Some say that one of the causes of dark underarm is dead skin cells. Have you tried having under arm scrub? There are salons that offer this plus bleaching. Hope this helps.

I got the same problem too...I had dark under arms since i was in college...what made it whiter? just lemon or citrus fruit...everyday, during bath time i rub citrus fruit on my under arm...it serves as deodorant too...after a month of doing it, i can proudly wear not just sleeveless but tube tops!!!!!! try it..