Build up
My hygienist reminds me occasionally when I go in for my cleaning that if I let things build up, they could lead to decay.
The same is true of what we keep inside: Bitterness, anger, resentment, unforgiveness, grief, anxiety, worry, or fear.
“…do not grieve the Holy Spirit of God, with whom you were sealed for the day of redemption. Get rid of all bitterness, rage and anger, brawling and slander, along with every form of malice. Be kind and compassionate to one another, forgiving each other, just as in Christ God forgave you.” Ephesians 4:30