How is botox brow lift or chemical brow lift?

Muscle relaxation: Botox causes a relaxation of the muscles in the forehead. Some pull the brows in and down while others pull the brow up. The best effect is for the Botox to block a mix of both. When you can not pull the brow in and down they tend to become spread apart and rise up a bit. This is the chemical lift you are talking about. There is also face lifts using Botox and dermal fillers

Botox: if injected properly, botox can be used to create a subtle and temporary browlift. Results last 3-4 months. Anecdotally, about 80-85% of patients who have a botox browlift are satisfied.

Opposing muscles: All of our facial expressions are made of 2 sets of muscles that oppose each others actions. The Botox lateral brow lift takes advantage of this by relaxing the muscles the draw the brow down, allowing the muscles that pull it up to take over, resulting in a lift.