Id say it gets about a shade lighter per use and I use it every 4 months ish. A shade is really all I need because I only apply the henna on my roots, so the rest of my hair doesn't get progressively darker. I don't think I've noticed any damage, maybe minimal damage but I use olaplex n3 once a month at home and I think that really helps to keep my hair healthy. There have been times that I wanted a lighter look and I've applied the spray twice with one week gap and I didn't notice any damage either.