Facial slimming is a very popular Botox treatment. When injected into the masseter muscles (the muscles on the jawline) in a circular manner, Botox can "slim the face." Botox relaxes the muscle and over time the bulk of the muscle is reduced lending to a less square and more oval or heart shaped lower face. When used for this face-slimming purpose, the onset of results and longevity is a little bit longer than when Botox is used to smooth out wrinkles on the face. You can start to see a difference in the face in about 10 to 14 days and the results should last about four to six months, but can be longer. In order to maintain the results treatments must be continued at regular intervals every 3 to 6 months.