coarsen

To make (more) coarse.

1941, Emily Carr, Klee Wyck, Chapter 6 "D'Sonoqua," http://www.gutenberg.net.au/ebooks01/0100131h.html She appeared to be neither wooden nor stationary, but a singing spirit, young and fresh, passing through the jungle. No violence coarsened her; no power domineered to wither her. She was graciously feminine.

[…] as the years went by, democracy and its wide audiences tended to broaden and coarsen humor.

To become (more) coarse.

He was intolerable now except under the influence of liquor, and as he seemed to decay and coarsen under her eyes, Gloria's soul and body shrank away from him […]

[…] though her skin had coarsened in the last ten years, the dark red of her cheeks and lips was as vivid as ever.