The basic principle of photoepilation, both laser and IPL is the phenomenon of selective photo – thermolysis that penetrates skin and is absorbed by melanin, the pigment of hair or hemoglobin – the blood pigment.
The light energy is absorbed by melanin and hemoglobin and converted into thermal energy. It then causes damage to the hair bulb and blocks blood vessels nourishing the hair matrix. After the treatment, the hair is removed and formation of new hair follicle is blocked.
Hair growth cycle plays an important role in the laser hair removal.
In the first phase of hair growth (anagen), hair reaches its full length; bulbs are open. Nutrition during this phase is carried out through the papilla connected to the bloodstream. This is the best stage to undergo an IPL treatment.
During transitional phase (catagen) the hair follicle shortens or regresses to a fraction of the length it was in anagen phase. At this time, the dermal papilla detaches from the hair structure. Hence, it causes the hair fibre to stop growing.
During resting phase of hair growth (telogen), hairs that were uprooted during catagen are typically shed. Depending on time the dermal papilla remains in resting mode, the phase can last 1-3 months. Around 10% of hairs are in the telogen phase at any given time. Because the hair fibre is not rooted in telogen, hairs can easily fall out or be removed through brushing, combing and plucking. The IPL treatment carried out at this time is inefficient because hair does not grow at the same time.
The IPL treatment needs to be repeated several times. Up to 30 percent of the hair can be removed after a single treatment. It is recommended to undergo 8 to 12 treatments with an interval of 4 weeks in between. Delaying or shortening the interval between treatments may affect the results.
Hair colour and skin type also pay an important role. The best results can be obtained with dark hair as the laser energy reaches the hair roots by melanin contained in the hair. Unfortunately, hair removal is less effective in case of very light hair. In addition, gray hair, which is completely devoid of color, has to be treated with a different method, i.e., E-Light.