Beth Moore, in her series on the Psalms, talks about dealing with sin that we hide - leaven. She mentions how leaven was equated with sin in the bible. Jesus talked about the leaven of the Pharisees, which Jesus said was hypocrisy, or self-righteous pride. But there are other kinds of sin that can be called leaven.
She talks about hypocrisy, Christians holding onto secret sins that we don't want to let go of and that we don't want to see or expose to anyone else.
She admonishes us not to hold onto even that little bit of sin that is left after we have dealt with sin, to not hold onto the leaven. The problem with leaven is that it gets into the dough and it ferments and causes the dough to rise. It becomes a problem.
That is my prayer - to be cleansed of leaven.