A masturbation addiction, or any addiction in general starts in the brain. Starting with a craving, loss of control, and continuing involvement. This can have effects/influence the brain depending on how long. A masturbation addiction can stem from many things in life whether that be past, or current stress, anxiety, previous trauma, current trauma, etc. This could be a way of coping from certain issues or certain situations, feelings, etc. If this is a concern to you. I would recommend seeking out professional help from a sex therapist, or someone who does specialize in addictions. There is hope, and it is possible to overcome this with the proper help and support.