My neck is darker than my face. i have had a lot of sun exposure and that lead to tanning.but by time my facial skintone became lighter whereas the area around my neck and my arms are still darker.Also i have been fussy while bathing, usually i dont focus much on cleaning my neck that resulted in accumulation of dirt. but now i do clean my neck twice a day but it is not getting any ligher.kindly help me with this.