Antonyms for "freshens up" include words like dirties, stains, soils, pollutes, and contaminates. These words have completely the opposite meaning of freshening up, which implies making something clean, new, or revitalized. To dirty something is to make it covered in dirt or filth, while to stain something is to leave a permanent mark on it. And if something is polluted or contaminated, it means that it is unfit for use or consumption. So while freshening up can refer to anything from personal hygiene to home maintenance, its antonyms suggest neglect, decay, and deterioration.