Skin condition?

On my upper side of my left arm my skin has began to change colores. Id say Im a light tan, and these spots are much lighter. At first it was a small amont, but now its spreading down my arm. Its not like it hurts, or fills ruff. Its just a bothersome. Self confidence runs low when your skin is miss match. Any who, I was wondering if any one knew the reason for these spots. If it would help, Id love to post some pic or what ever it takes.