Hair grows in cycles, and laser will only work on growing and mature hairs. Repeated sessions will be needed to treat hairs in successive growing phases. A minimum of five or six sessions, eight weeks apart, are needed to obtain definitive reduction. Less sessions are needed for larger body areas like legs, arms or back and the time interval is longer between treatments. At each session, there is less hair and the hairs become finer. Touch-up sessions may be needed to treat persistent hairs.
Other conditions that may affect the number and success of the treatments include age, the colour of the skin(the darker the skin, the more treatments needed) and any hormonal problems or treatment (which may stimulate hair to grow from the dormant stage).