Maturate
Part of speech: verb
Definition: To mature to achieve suppuration
Fester
Part of speech: verb
Definition: To become septic; to become rotten.To worsen, especially due to lack of attention.
Example sentence: As a child growing up in San Francisco in the 1950s, I sometimes met insults when I ventured outside of Chinatown or my neighborhood. I have even been spat on and threatened with a knife. I could have let my anger fester until it became hate. However, I realized they were isolated incidents, and I simply got on with my life.