The lines that appear between your brows actually result from muscle movement over time. When these muscles contract, they draw the brows together and repeated frowning can result in moderate to severe frown lines between the brows. Botox is a purified protein that is injected in a simple non surgical procedure that temporarly improves the appearance of moderate to severe frown lines. This happens because Botox relaxes the muscles causing the frown lines so when you try to frown the frown lines largely do not form. For most people, Botox will remain effective for 3 to 4 months.