This is quite common in darker skin types if you wax or shave under your arms. The trauma to the skin causes the skin to become sensitised and then it hyperpigments as a means of protection. If this is the case with you, you may need to consider other form of depilation under the arm,such as laser hair removal. Quite a few of our patients use one of the serums we stock at Skin Renewal called "Brighter Concentrate", for the under arms and bikini area, but under stand that this is going to then be a lifetime product use, as it is not going to take away the trauma caused by waxing or shaving… it is only going to deal with the skin’s reaction by slowing down the pigmentation process.