The pigment under my armpits is much darker then the rest of my skin. no matter how much i scrub it wont lighten. my hair is blonde. ?

Dark pigment: This can be normal for some people. Scrubbing it will tend to make it worse because anytime the skin is irritated it can heal lighter or darker than normal the irritation can cause the melanocytes to produce more pigmentation. Certain conditions, like acanthosis nigracans are notorious for causing increased velvety pigmentation around the neck, under the arms and in the genital area.