this is true; I have a physical scar to prove it! God is good and gracious as He revealed this anger, bitterness and envy to me so I could repent of it. I have been physically and spiritually healed for almost 40 years now. do I still struggle and do battle in this area? you bet! however, I serve the Overcomer, Jesus, and He is my Advocate and Defender. Praise His Name!
I think a lot of anger comes from fear or misunderstanding. These feelings trigger adrenaline and negative endorphins which can 'rot' your insides. We have to rely on our Lord to bring us out of our anger and towards peace.