One treatment will definitely show improvement, but not the longer lasting results that one can demonstrate after two or three serial treatments. Think about the fact that in most Halo treatments, the density of the treatment(as compared to depth of treatment)is usually 20-30%, meaning that only 30% max of your entire skin will develop those MENDs. This allows for fast and predictable healing, but if you do the math, it will take up to 3 treatments for your skin to get close to 100% of the areas treated. It takes even more treatments off the face as density settings need to be lower when off the face. Spacing between treatments should be 6-8 weeks or more. It is amazing to see your skin continue to improved far beyond the initial healing.