You should blame dirty pillows and phones if you have acne on your cheeks. E. coli and other bacteria can also be found on your phone. When you hold your phone to your face, you're introducing bacteria to your skin, which could lead to more acne. Dirty phones, pillowcases, and other habits like touching your face are common causes of persistent acne on one side of your face. Cleaning your smartphone with a disinfectant wipe regularly might help prevent breakouts. Also, at least once a week, change your pillowcases.