The three most common facial areas treated with Botox for wrinkle reduction are the frown lines (vertical wrinkles in the glabella area, between the eyebrows), the “crow’s feet” area in the temple to the side of the eyes (caused by squinting), and the horizontal forehead wrinkles (caused by raising the eyebrows). Of these three, the “best” area to treat with Botox is the frown lines. This is because the treated muscles (corrugators and procerus) can be totally paralyzed with no negative side effects. Frowning is a universally negative expression (not necessary unless you want to look mean or angry or are an actor who is playing the bad guy), so there is no downside to being unable to do so.
Botox treatment of the forehead (frontalis) muscles (there is one on each side of the forehead) will improve horizontal forehead wrinkles, but if these muscles are too weak, the position of the eyebrows will go lower. A lowered brow will increase redundant skin in the upper eyelids and thus make this area appear heavier with a “tired” look. People undergo upper eyelid blepharoplasty in order to reduce skin redundancy in this area. Because there is a downside to over-treating the frontalis, the goal in treating the forehead should be to weaken these muscles but not to totally paralyze them.