I'm one lucky girl as I don't sweat much! Meaning, I can run a mile and still look HOT (not!) Kidding aside, I really don't sweat much so I can skip using deodorants or anti-perspirant and probably use them only if I know I'll be staying outdoor for long or I'll be doing some strenuous activities! That's the reason why my underarm doesn't turn dark (knocks on wood). Yes, some or shall I say, most deodorants can make our dear underarms turn dark and ugly! Why? Well, these roll-ons, sticks and sprays may contain parabens, PEGs, synthetic ingredients or aluminum compounds that could cause darkening or irritations. So best way to keep your underarm in its' most natural, gorgeous form? Use 100% natural deodorants but seriously speaking, it is very difficult to find one! But of course, we can always go to our trustee "tawas" (a natural white crystalline mineral salt of potassium) which I think is great but I find it tedious to apply (cause I'm one lazy woman of the 21st century!)
Recently, I've discovered a locally made deodorant from Human Nature's 100% Natural Premium Deodorant in Powder Fresh.

