I noticed it falling out when I ran my fingers through it at about 18 or so. By 21-ish, I could see it noticably thin at the top back of my head. It really freaked me out and I started using Rogaine on it. The stuff works as long as you remember to put it on twice daily. Most of the hair came back, but if I start slacking on the application, the thinning is noticable. It doesn't do anything about your forehead, though and I have a noticable widow's peak.