Thank you for your inquiry, Beaulah. Pigmentation can be caused by a number of triggers. What is quite common, especially among people with darker skin types, is the occurrence of post-inflammatory hyperpigmentation (PIH). This happens when the skin becomes injured, and the body pigments in that area as a protective mechanism. So under the arms, if you wax or shave, you are injuring the skin and therefore that area will pigment. In your neck, it is quite common to get PIH if you are wearing collars or scarves regularly, due to the heat and the friction caused in the neck by the clothing. You can use a tyrosinase inhibitor to help suppress the pigmentation from forming. Something like Brighter Concentrate by Lamelle works very well on the body. It is also advisable (especially in your neck area) to ensure that you are using a broad spectrum SPF every day.