Friction: This is as a result of different methods of hair removal from the underarm region, which include shaving, waxing or use of hair removal creams. All these methods brings about friction on the skin and constant friction on the skin changes the color of the skin. To reduce this friction on the skin, it is advisable not to use waxing method to remove underarm hair, however you can just shave it with a thick layer of shaving cream which reduces the friction between your skin and the blade of the shaving stick. Then always apply moisturizer immediately after shaving the underarm region.
Chemical irritation: This is as a result of lotions, deodorants and perfumes which is used on the underarm region. These chemicals though gives dryness and fantastic scent but has a burning effect over a long period of time. This leaves a dark coloration behind which disfugure the underarm region. The only possible solution to this is to stop using deodorants or perfumes on the underarm region instead we can use anti-perspirants or talcum powder, these make the region dry also thereby reducing bad odor and discoloration.
Fungal infections: This is as a result of excessive perspiration, excessive sweating or when the underarm is always wet. This leads to the growth of fungi in the underarm region causing a discoloration even after the fungi have being treated and gone. Use anti-fungus powder on the underarm region to help prevent fungi infection at the same time keeping it dry.
To remove this discoloration at the underarm region, apply moisturizer with bright components like vitamin C and kojic acid to the region at night every day before going to bed, changes won't start to occur until about 3-4month of constant application.