deteriorate

To make worse; to make inferior in quality or value; to impair.

to deteriorate the mind

The art of war, like every other art, ecclesiastical architecture alone excepted, was greatly deteriorated during those years of general degradation[…]

To grow worse; to be impaired in quality; to degenerate.

During this fine run through Fife the weather had deteriorated rapidly, and as we passed Wormit and came onto the Tay Bridge heavy rain clouds were piled over the sea.

The condition of the tunnel continued to deteriorate, aggravated by the vibration from the heavy traffic, and stories of trains emerging with dislodged bricks on their roofs are probably not exaggerated.