In most cases, all of it! But over a period of weeks new hair will grow and you will need additional treatments. Let me explain why by first explaining how hair grows. There are three phases of hair growth - anagen (the growth phase), telogen (the resting phase) and catagen (the period of transition.) The phases of hair growth last for varying periods of time in different areas of the body. For example, the hair on your face is in its anagen phase 50-70% of the time, while the hair under your arms only actively grows about 30% of the time. The telogen phase also varies in different areas of the body. Only hairs in the active growth phase (anagen) can be successfully treated each time. Thus, a series of treatments are scheduled to ensure that all the hairs will be targeted as they leave the telogen phase and enter the anagen phase. Missing scheduled appointments will increase the number of treatments required.